COP v3.0:other-products;

15 Other Products 

Other roofing products, include:

  • Curved Roofs.
  • Solar Units.
  • Pressed Metal Tiles.
  • Standing Seam Cladding.


15.1 Curved Roofs 


There are two main methods to clad curved buildings.
  1. Draped sheets, known as spring curving.
  2. Pre-curved sheets, either roll-curved or crimp curved.

For compliance with the requirements of the NZBC, designers should abide by the limitations of profiled metal cladding for curved roofs.

The curving process or crimping does not produce any strength enhancement for point or wind load. Curved roofs usually have maximum purlin spacings to avoid distortion.

Designers and contractors should be aware that light gauges such as 0.40 mm steel and 0.70 mm aluminium are likely to show distortion when used for curving.When asymmetrical-pan trapezoidal cladding is used for curved roofs and appearance is paramount, a heavier gauge cladding should be specified.

They are 'Restricted Access' roofs, which means that walking traffic should be restricted to within 300 mm of the purlins, and in the pan or over two ribs if they are adjacent to the vertical lap. Because of the changing pitch, edge protection must be provided, or a safety harness used when installing curved roofs. See 13 Safety.

All side laps of curved sheets below the minimum pitch for the profile must be mechanically fastened and sealed.
Curved flashings are described in 8.4.5 Curved Flashings


15.1.1 Spring Curving 

Spring curving, also known as draping or arching of roofs, is a method of providing continuous lengths of roof cladding over a curved roof structure from eave to eave without a ridging. It is suited to symmetrical roofing profiles of low rib height, which can follow a curve without excessive panning or distortion.

Because these profiles do not have a large rain- water carrying capacity they are limited in radius and length.

Maximum radius is limited to provide adequate drainage at the top of the curvature and minimum radius is limited to avoid distortion without pre-forming.

Asymmetrical and tray roof cladding can be draped , but only to a large radius before panning or distortion occurs and they are , therefore , unsuitable for all except large radii. They do not have the same restrictions on rain- water carrying capacity as symmetrical claddings. Because corrugate cannot be satisfactorily turned down into a gutter, wind pressure can drive rain up the corrugations, causing 'blow back' and allowing water ingress. Spring curved corrugate should not terminate below 8°.


Roof cladding must not terminate at a lower pitch than that permitted for the profile , unless the designer can demonstrate compliance with the NZBC by detailing an alternative method of weathering and durability.

All trapezoidal and tray roof cladding below 8° must have the pan turned down into the gutter.

All roof cladding at all pitches must have either a pull-up or a dog-eared stopend.


If the width and height of the roof are known, this information can be used to obtain the radius of curvature and subsequently the sheet length and the length of seal required for any profile.




Only G550 MPa grade (HS) coated steel is recommended for drape curving.

Tables 4.9.1.A & B assume the cladding is draped over an arc where the base chord is parallel to the ground. When the base chord is on an incline the maximum radius can be increased.

If the width and height of the roof are known, this information can be used to obtain the radius of curvature and subsequently the sheet length and the length of seal required for any profile.


15.1.1C Spring Curving Calculator

Width = w=w
Height = h=h
Radius of curvature = r=r
Minimum pitch = p=p°
Sheet length = l=l
Length of seal = s=s

The Code of Practice Online provides an interactive tool for these calculations. This tool is only available online at 15.1.1C Spring Curving Calculator

Enter width and height to calculate:
Width and Height not valid - please re-enter 

Full Calculation Details and Example
Start with : w = Width of roof
=  12
Start with : h = Height of roof
=  5
To find r the radius of curvature
r  =  
4h²+ w² 8h
(4 x 25) + 400) 40
=  12.5
To find l the sheet length
Find the length y
y = r - h
=  12.5 - 5
=  12.5
Find the length x
x  =  
w 2
20 2
=  10
To find the tangent of angle A
tan A  =  
x y
10 7.5
=  1.33
To find angle A
A  =  aTan(
x y
=  aTan(1.33)
=  53°
Find the arc length c b
c b  =  
2 π r A° 360
2 x 3.1412 x 12.5 x 53 360
=  11.56
Find the sheet length l
l  =  cb x 2
=  cb 23.12 + 100mm
 =  23.12
To find the length of seal
p = Min Pitch for corrugate = 8°
s  =  r x (tan 8°)
=  12.5 x 0.1405
=  1.76


N.B. This length of seal is required on each side of the crest.
It is recommended that all profiles be sealed to 8°.

If the sheets are lapped laterally they must be sealed.

15.1.2 Laps 

By definition, a curved roof is flat at the crest of a curve, and because it is below the specified minimum roof pitch required by the NZBC for unsealed laps, side laps should be sealed over the crest of the arch until the minimum pitch is reached.

All vertical laps should be sealed if the pitch is less than the allowable minimum as tabulated below:

15.1.2A Curved Roof: Sealed Lap Pitch

Minimum pitch below which vertical laps should be sealed
Symmetrical Low Trapezoidal
Asymmetrical Low Trapezoidal
Secret-fix Tray


When the pitch of the roof is below the minimum, the side lap is required to be sealed over the crown, and lap tape or silicone sealant should be placed on top of the rib and firmly held down while fixing takes place. Intermediate side stitching is required at the midpoint of all side laps using self-sealing rivets or stitching screws.
The side lap of profiled sheeting is designed with anti-capillary provisions to be self-draining.
Before the continuous manufacture of corrugate from coil, symmetrical corrugate sheets were often laid with two nesting laps, which commonly corroded due to condensation, even when the laps were primed. All metal profiles now produced in NZ have capillary grooves. Trapezoidal profiles are designed for one lap only and corrugate used for roofing is designed for 11/2 laps with an under and an over.
Avoid double lapping because condensation can become trapped in the lap, which can cause accelerated corrosion with all steel products, including pre-coated steel. Lap priming should not be used as the permeable paint surface can retain moisture and accelerate corrosion.

15.1.3 Transverse Laps 

To avoid a transverse lap, or if the sheet is longer than can be transported or safely handled, a step in the roof structure should be provided. See Step Apron.

At a step or a lap, the end span must be reduced. See 3.5.1 Point Load.
If a transverse lap cannot be avoided, it must be mechanically fastened and sealed and must be made watertight from the inside by lap tape or sealant.

The sealant should ensure that the condensation flows past the joint and either be absorbed by the underlay or drain to the eave.

Severe corrosion problems have been caused on curved roofs by condensation running down the inside of roof cladding and into the laps. This was a common mode of failure when short lengths of galvanized corrugated sheeting were used in the past, but long run roofing without end laps has significantly reduced this type of failure.
Do not assume that the paint coating would provide barrier protection. The manufacturers' and industry requirement, since 1995, is to seal all transverse laps.
The time of wetness, which is a major factor of corrosion, is increased when unsealed metallic coated steel cladding and flashing laps are subjected to a continuously damp environment. This situation is also detrimental to pre-painted metal cladding, which are attacked through the permeable paint coatings and at cut edges.

Where a draped roof is regarded as too long to transport or too difficult to handle as a drape curve in one sheet, the crown sheet should be as long as practical and the transverse lap should be placed as far down the roof as possible to increase the pitch at this point.

At the termination of curved sheets at minimum pitches in exposed areas, additional weathering is required at the turn down. Ventilated filler blocks and/or baffles should be used to prevent blowback, which can cause corrosion because the underside of the sheeting becomes an unwashed area.

Penetrations or end laps must not be placed in the region of the curve where the roof pitch is below the minimum pitch for the profile in 7.1.1A Minimum Recommended Pitch.
Additional timber or steel supporting structure must be installed upside and downside of any penetration hole greater than 300 mm x 300 mm to provide fixing for the sheet and a reduction of the end spans.
Support must be provided to resist the uplift on sprung curved sheets at all penetrations.
All side laps of curved sheets below the minimum pitch for the profile must be mechanically fastened and sealed.

Continuity over a minimum of three purlins is required for successful drape curving and therefore any interruption, such as a penetration or other cutting of the sheet, may require machine curving to ensure the curvature is maintained.

Purlins must be accurately positioned with the top faces tangential to the radius of the arch and should be within a 5 mm tolerance to avoid purlin creasing. Roof traffic should be restricted to avoid damage, particularly in the low pitch region or in highly visible areas. Damage as a result of walking traffic can be seen as creasing at purlin lines or canning in the profile pans.
Some purlin creasing is to be expected with stronger profiles, and at low pitches this can cause corrosion due to ponding. For convex roofs, the minimum radii should be adhered to because the pans are in compression, whereas with concave roofs the pans are in tension and the panning or distortion of these roofs will be less , although it depends on the profile.



Only vented profiled filler blocks should be used at the eave on curved roofs so that some air movement is provided within the ribs. See 10.10 Ventilation Pathways.
Provision for expansion should be provided in the same manner as required for straight lengths, but the configuration of curved roofs means that some expansion will be taken up by a springing of the profile further up, which results in less movement. When the total sheet length is considered for expansion, positive fixing using oversize holes, should be made at the crown.

15.1.4 Durability 

When draped curve roofs are unlined and used as canopies or exposed eaves, the underside of the sheeting becomes an unwashed area. Therefore, it needs to be washed and regularly maintained to comply with the durability requirements of the NZBC and the supplier's warranty. The underside of pre-coated roof cladding is provided with a primer and backer coat only; it is not as weatherproof or UV resistant as the top-coat.

Because pre-painted cladding is not intended for use in this micro-climate without regular maintenance, the underside of the soffit should be lined in all severe and very severe environments.
(see 16 Maintenance )

15.1.5 Purlin Spacing 

When the purlin spacing is close to the maximum allowable for the profile and ease of curvature, the roof cladding is more likely to be damaged by foot traffic and distortion between the purlins. When the radius of curvature is close to the minimum, the purlin spacing should be reduced to the end span distance for each gauge and profile. See 3.17 Steel Cladding Wind Load Span Graphs.

Access on curved roofs should be restricted and be regarded as Type B, and extra care should be taken during installation because of the changing pitch. Because some profiles used for curved roofs are close ribbed, it is not possible to walk in the pan. The walking pattern should be restricted to within 300 mm of the purlin and the load spread over two ribs. This is more important when low strength steel is used for pre-curved sheets.

Avoid using 0.4 mm G300 steel or 0.7 mm aluminium for roof cladding subjected to walking traffic.

The designer should consider the radius of curvature, profile, thickness, grade, and purlin spacing as these are all related parameters of curved roof design.

Maximum purlin spacings should be adhered to and any sheets damaged by foot traffic in the area below the minimum pitch for the profile should be replaced.

All curved roofs must have end spans reduced to two-thirds of the intermediate span, as required for straight roofs because the kl load - factor requires a reduction in purlin spacing at the roof edges. Where translucent sheets are required to be curved, the normal purlin spacings should also be reduced.

If the design loads are high, or where the eave is not lined and the roof cladding is exposed, extra fixings and load spreading washers are required.

It is important that the radii limitations and water drainage characteristics for specific products are considered at the building design stage so that water runoff over the low pitch region will not exceed the maximum for the profile used. The maximum radius of curvature permissible for corrugate and symmetrical profiles is limited for this reason.

Bull-nosed verandah or lean-to roofs, which are simply supported spans and do not have the continuity required for point load, should have their purlin spacings reduced to less than normal end spans.

Because the sheeting is continuous over the top of a curved roof and the wind dynamics are different, purlin spacings do not need to be reduced at the crest, as is normally required at the ridge on gable or hipped roofs.

The two top purlins should be placed to enable the sheeting to follow an arc that minimises purlin marking.

Draped curved roof or curved ridges should be fixed by fastening each sheet first to one side of the roof and then pull it down to be fixed on the other side. Alternate sheets should be laid in sequence to avoid cumulative errors and be laid from opposite sides of the roof to ensure squareness is maintained. Shift the two top ridge purlins to provide an even radius.


Because extra uplift load will be taken by the end fasteners, screws and load spreading washers should be used on the penultimate and the last purlins and screws are the preferred fastener for curved roofs, although nails may be used on intermediate purlins.

Rafters and purlins must have additional fixing to the structure to resist the additional uplift load at the eave caused by curved sheeting.
Any assumed increase in span due to an increase in strength of the roof curve should be discounted, as concave and convex draped curved roofs are limited to the maximum purlin spacing allowable for the particular profile, and are dependent on the wind design load.



15.1.6 Concave Roofs 

Roofing can be spring-curved into concave shapes however designers should be aware of the limitations on the minimum pitch where the curve is terminated, the extra uplift load that will be taken by the fasteners at the centre of the curve, and take into account the catchment area of the roof.

The pitch for concave roofs must not be less than 8° for corrugated profiles, 4° for symmetrical trapezoidal profiles, and 3° for other profiles. Screws and load spreading washers must be used for fixing cladding on all sprung concave curved roofs. The purlins must have additional fixing to the structure to resist the extra uplift load on sprung curved sheets.

The additional load produced by draping concave and convex metal roof cladding depends on the radius of curvature and the thickness of the metal. The induced load has two forces:

  • additional load on the fastener; and
  • additional load on the purlin/rafter or truss connection.

Although the former is the responsibility of the roofer, the COP recommends that the purlin connection is inspected for adequacy. The connection prior to any additional load imposed by the draped roof will be determined by table 3.6. An economical solution to the increased connection load is to use a proprietary purlin strap.





15.1.7 Pre-Curved Roofs 

Low tensile metals and G 300 coated steel can be easily roll-curved in a pyramid rolling machine to small radii and can also be crimp curved into these shapes. See 15.1.9 Crimp Curving.












15.1.8 Roll Curving 

Pre-curved corrugated roof cladding is used for bull-nosed verandah roofs, ridges, or for roofs where the radius is less than the minimum required for sprung or draped curved roofs.
Corrugated (symmetrical sinusoidal) G300 roof cladding is easily curved or bull-nosed. The sheets are passed through matching curving rolls, which progressively form curves in a wide range of radii. If G300 and G550 steel sheets are to be used together, because these two materials will not have matching profiles, adjustment of the roll-forming machine setting is necessary.

Circular barns have been successfully cladded with 0.4 mm steel for many years, but 0.55 mm steel or 0.9 mm aluminium should be used for roll-curved roofs subject to foot traffic. G300 coated steel of 0.4 mm and 0.7 mm aluminium are only suitable for roofs without access or for wall cladding.

G300 steel can be curved to a radius as small as 300 mm using pyramid curving rolls. There is, however, a straight portion of about 80 mm at the end of the sheet which may need to be trimmed off if a true curve is required.
If the edge of the sheet is too flat or long, rippled edges may result, and these should be dressed out using a dressing tool or trimmed off before the sheet is installed.


A curve can be rolled on one end of a straight length of roof cladding to provide an over or cranked ridge, but for ease of fitting and transport, a lap is usually made at the first purlin down from the ridge. This should be sealed in the same manner as is required for any transverse lap.
An alternative ridge detail can be used with straight sheets, without any lap, by roll curving or draping the cladding over the ridge, where the ridge purlins are extended their maximum span.
For safety, roofs which are often used as a means of access to or onto a verandah should be provided with an intermediate support. Simply supported roofs cannot withstand foot traffic to the same degree as continuously supported sheeting.

15.1.9 Crimp Curving 


Crimp curving is applicable to all profiles, but it is most suited to asymmetrical sections that cannot be rolled or drape curved.

Crimp curving is produced by pressing a small crimp in either the tops of the ribs or the pans of the sheeting. The profile is progressively shortened at these points causing it to bend. The radius can be altered by the spacing of and the number of crimps.

Some machines are capable of forming high-strength steel by a combination of compression and tension in the die design, and some machines require the use of strippable film as a lubricant to avoid coating damage. Where sheets are to be end lapped and different strength materials are used together, machine adjustment is required to ensure an acceptable fit because their profiles are not usually consistent.

Fitting curved sheeting requires considerable care to ensure a satisfactory and aesthetically pleasing job. Setting out requires first checking that the materials delivered on site are within specified tolerances, and before commencing work the building should be checked for squareness.

The curving process can cause dimensional changes, which can lead to misalignment, so the sheets should be kept square with the building. Some minor saw-toothing at the gutter end is to be expected when fitting curved sheeting. When multiple curves are required that cannot be provided on one sheet, the sheets should be fixed in the order shown in 15.1.9A Fixing Order: Curved Sheets.



All transverse laps of crimped curved roof cladding must be mechanically fixed and sealed.

Some paint checking and microcracking is likely to occur at the crimps on metallic coated steel cladding and these may show a white bloom. This is more readily seen in unwashed areas, such as when crimp curved sheets are unlined as a canopy or over a walkway roof. This area is required to be washed regularly under the maintenance provisions of the supplier's warranty.

The underside of colour coated roof cladding is provided with a primer and backer coat only and if this is exposed in an unwashed area and can be seen, it should be post-painted with two coats of Acrylic paint. These areas are subject to maintenance as an unwashed area. (see over-painting section 13.7) Because the top of crimped sheeting is also subject to the collection of dirt and debris, particularly at the low pitched area, it is subject to maintenance requirements.

All side laps of crimped curved sheets below the minimum pitch for the profile must be mechanically fixed and sealed.

15.1.10 Timber Fixing 

When attached to timber purlins, the longitudinal wires of the safety mesh must be either bent down and fixed to the sides of the purlins or fixed to the tops of the rafters by 40 mm galvanised steel staples with a 3.15 mm diameter and spaced at 150 mm.

Staples must be driven so that a cross-wire is between the end of the wire and the staple, or the end of the wire is bent back and twisted four times around the same wire so that individual wires cannot be drawn from a staple.


The longitudinal wires must be fixed to the purlins or rafters by galvanized steel wire loops of not less than 3.15 mm diameter. Place the centre of the tying wire around the longitudinal wire at an intersection, so that a transverse wire is between that point and the end of the longitudinal wire.

The tying wire must be passed once completely around the rafter, and then drawing the two tails of the tying wire in opposite directions over the two strands of the tying wire and twisting together with at least three complete turns.



When joining rolls or sections, the two transverse wires must be placed together and the longitudinal tail wires must be twisted around each other. One longitudinal tail wire must be twisted four times around the main portion of the same wire. The other longitudinal tail wire must be twisted once around the main portion of the same wire and then four times around the two transverse wires


15.2 Mounting Air Conditioning, Aerials, and Solar Units 

Structures mounted on the roof requires consideration of all the factors contributing to the performance of the roof cladding.

Some structures which are commonly mounted on roofs include air conditioning units, aerials, photovoltaic systems, and solar water heating units.

Design and installation of these structures should consider at least three areas of performance:

  1. Structure – the effect of mounting the structures and roof traffic for ongoing maintenance; see 3.9 Dead Loads and 3.6.2 Roof Traffic.
  2. Durability – corrosion may result from issues such as wet contact, capillary action, unwashed areas, material compatibility, and runoff; see  4.10 Other Causes of Corrosion.
  3. External Moisture – penetrations influence roof drainage and can affect weatherproofing of the cladding; see 9.3 Penetration Durability and Compatibility.


15.3 Pressed Metal Tiles 

15.3.1 Design 

Metal tiles, shingles and shake panels are press formed to provide a variety of shapes resembling clay tiles, wooden shingles or shakes. They are interlocked or overlapped laterally and longitudinally and are clipped or fastened to timber or steel battens.
Metal tiles, shingles and shakes are metallic coated steel are manufactured from metallic coated steel, although aluminium or other metals can also be used.
Pressed metal tiles made from steel invariably have an additional protective coating applied over the metallic coated steel. This may be an organic paint coating applied by either the steel manufacturer before the tiles are formed or by the tile manufacturer after the tiles are formed. An alternative coating can be provided by applying crushed stone or ceramic granules to the base metallic coated steel and attached by an adhesive coating; normally, a clear acrylic coat is used.
These coatings give protection to the metallic coated steel base, as well as providing a decorative finish.
Pressed metal roofing tiles are installed by fixers, trained and appointed by the manufacturers or their representatives, and they are not normally supplied to other installers. Durability 

The principles behind detailed requirements for fixings, flashings, corrosion, compatibility, and maintenance as described elsewhere in this COP should also be applied to the design and installation of pressed metal tiles.

Exceptions result from the specific differences between tiles and other forms of metal roof cladding, and include the height of laps and specific dimensions of metal shingles and shakes prescribed in this section.

Steel based metal tiles, shakes, and shingles must have hot-dipped galvanised fasteners that are compatible with the base metal and provide a service life equivalent to the durability of the panel.
Panels are fastened to the roof structure by fixing horizontally through the front of the panel; and because the fixings are in shear, they provide wind uplift resistance suitable for very high wind design loads. Pitch 

Tiles with a minimum upstand of 25 mm must not be laid on roof structures less than 12° unless approved in writing by the tile manufacturer, the B.C.A. or the Territorial Authority.

Tiles, shakes or shingles with an upstand of less than 25 mm must not be laid on roof structures less than 15°.

N.B. The pitch of the roof is not the same as the pitch of the tiles because this varies with the height of the batten and the height of the upstand. If the minimum pitch cannot be complied with, a method approved in writing or a producer statement should be given before work is commenced. Underlays 

Permeable self-supporting underlay must be installed on all new roofs as specified in section 4.3. of this Code of Practice.
The underlay must be installed horizontally with a minimum overlap of 75mm.

The first length of underlay should be positioned so that it lays over the eave batten and the fascia, and into the gutter.

When pressed metal tiles are installed, the underlay is laid horizontally on top of the rafters before the battens are fixed, and so there is an air space between the underlay and the tiles, except at the eave. Roof Framing 

Roof framing should provide support and fixing for the tile battens that will satisfy the design load wind requirements. Installers should check that the framing has been erected to an accurate and even line before roof fixing is started.

An inspection and any rectification to the framing alignment must be carried out before roof fixing is commenced. Tiling Battens 

Tiling battens must be:
  • H1.1 boric treated when used in attic roof construction;
  • H1.2 treated when used in skillion roof construction;
  • Douglas fir with a moisture content of less than 20%;
  • KD Pinus Radiata with a moisture content of less than 18%;
  • a minimum of 50 mm x 40 mm for 900 mm rafter spacing; and
  • a minimum of 50 mm x 50 mm for 1200 mm spacing.
Copper preservative timbers must not be used with Zincalume coated tiles. Battens required for rafter spacings greater than 1200 mm must be specifically designed and be spaced to suit the tile module.
Battens at 370 mm centres must be fixed to the rafters or trusses over the underlay using fasteners to comply with Tables 10.1.5.A, B and

N.B. Battens at different centres may require different values. Batten Installation

  • Battens must have square cut ends and must be butt jointed over the centre line of the rafter.
  • Adjacent rows of battens must not be joined on the same rafter and must span at least three rafter spacings at the roof edge.
  • A batten must be installed immediately behind the fascia as fixing for the eaves tiles.
  • Eaves tiles must overhang the gutter by a minimum of 30 mm.

Eaves tiles are recommended to overhang the gutter by 40 mm.

Because an eaves-tile batten is installed immediately behind the fascia the position of the next batten up the rafter will be less than that of the normal tile batten spacing. The position of this batten may vary depending on the pitch of the roof.

The edge of the roof should be taken as 20% of the roof width measured from the fascia, barge, hip or ridgeline, and will apply all around the periphery of each roof plane.

The batten layout is marked on the rafters by placing nails at the line of the batten fronts. The roofing underlay is laid over this, onto the rafters. The battens are then laid from the lowest part of the roof upwards, using the marker nails to locate the front edge of the batten. The marker nails are removed before the tiles are laid. Pullout resistance for different constructions Pullout resistance in kN required for battens for buildings with ceilings

cpe = -0.9, cpi = 0, cp = 0.9

Purlin/ batten sizeMax spanWind Zone 0.61kPaWind Zone 0.61kPaWind Zone 0.82kPaWind Zone 0.82kPaWind Zone 1.16kPaWind Zone 1.16kPaWind Zone 1.50kPaWind Zone 1.50kPa
mm x mmmmLow 32m/sLow 32m/sMedium 37m/sMedium 37m/shigh 44m/shigh 44m/sVery high 50m/sVery high 50m/s
50 x 409000.
50 x 5012000.
M = main body of the roof P = periphery Pullout resistance in kN required for buildings without ceilings (but with a permeable
windward wall)

cpe = -0.9, cpi = 0.2, cp = 1.1

Purlin/ batten sizeMax spanWind Zone 0.61kPaWind Zone 0.61kPaWind Zone 0.82kPaWind Zone 0.82kPaWind Zone 1.16kPaWind Zone 1.16kPaWind Zone 1.50kPaWind Zone 1.50kPa
mm x mmmmLow 32m/sLow 32m/sMedium 37m/sMedium 37m/shigh 44m/shigh 44m/sVery high 50m/sVery high 50m/s
50 x 409000.
M = main body of the roof P = periphery Pullout resistance in kN required for buildings without ceilings (and with a dominant
windward opening)

cpe = -0.9, cpi = 0.8, cp = 1.7

Purlin/ batten sizeMax spanWind Zone 0.61kPaWind Zone 0.61kPaWind Zone 0.82kPaWind Zone 0.82kPaWind Zone 1.16kPaWind Zone 1.16kPaWind Zone 1.50kPaWind Zone 1.50kPa
mm x mmmmLow 32m/sLow 32m/sMedium 37m/sMedium 37m/shigh 44m/shigh 44m/sVery high Very high 50m/s 50m/s 
50 x 409000.
50 x 5012000.
M = main body of the roof P = periphery Tile Batten Fastener Requirements

Gun nail90 x 3.1510.4
Ringshank nail (gun/hand)90 x 3.210.6
Gun nail90 x 3.1520.7
Twist Shank Nail90 x 3.310.9
Purlin Screw c/s head10g x 10012.5
Type 17 screw14g x 10017.3


15.3.2 Valleys 

Valley gutters must be made of the same metal or coating as the roof tiles or a compatible material, and when the roof tile is painted or coated the valleys must also be painted.

Where secret gutters are used or where the flashings are unseen, they must have a durability of 50 years.

The valley must have a minimum upstand of 20 mm, and the fasteners must not penetrate the valley.

For valley sizing, see 5.6.1 Valley Catchment.


15.3.3 Roof Traffic 

Metal Tiles are classified as a Type B roof cladding as they cannot be walked on indiscriminately without the risk of damage.

Persons authorised to walk on a metal tile roof must walk only in the pan of the tile where the batten supports it, and wear flat, soft-soled shoes to prevent damage to the tiles and surface coatings.
Other trades must be made aware by the contractor or site supervisor of the method of walking on pressed metal tiles without causing damage, and that the cost of repairing damaged tiles is their responsibility.

15.3.4 Valley Installation 

See E Metal Tile Valley

The valley boards installed between the valley jack rafters to support the valley and tile battens are required to be set with their outer edge at a minimum of 90 mm from the centre line of the valley. Valley boards are required to support a point load of 1.1.kN, which is taken to be the weight of a tradesperson with a bag of tools.
Valleys are installed so water discharges over the back and into the eaves gutter. The valleys are held in position by clips specially designed to allow for expansion, or by compatible nails and washers placed alongside the valley or bent over the top lip of the valley.
Under no circumstances must the fasteners penetrate the valley surface.
Joints cannot have an overlap of less than 200 mm.
The top end of the valley should be turned up against the hip or ridge battens to the height of the batten. Where two valleys meet over a dormer, they are cut, shaped, joined, and sealed so that they form a continuous valley.
The tile edge should be bent down to a minimum of 5 mm from the valley floor.
The gap between tiles on opposing sides of the valley must be a minimum of 70 mm.
Valley boards and boards supporting flashings must be H.3 treated, and all metal and timber should be separated by underlay .

15.3.5 Flashings 

Standard flashings are supplied for most locations on a roof, and are in two styles, only one of which is used on any one roof. All flashings and roofing accessories are made of the same base metal as the tiles.

  • Long accessories are 2 m long with fixing holes every 500 mm and there are specific accessories for ridges, hips, barges, aprons and walls.
  • Short accessories are 400 mm long trims and can be used for most flashing applications on a roof.

Special flashings are made as required by the manufacturer or the roofer from uncoated steel, and subsequently factory coated using the same coating process as used for tiles. Ridge 

Tiles must be turned up to a minimum of 40 mm against the battens, hip board or where they butt against a vertical or an inclined surface.
The ridge trim cap or side flashings must cover the tile turn-ups by a minimum of 35 mm.

Ridge tiles are bent up and then cut to form a turn-up that fits under the ridge/hip cap or short accessory. To ensure a watertight joint, a tight fit is required between the tile and the ridge cap.






Hip Hip 

Tiles should be turned up against the battens or hip board by a minimum of 40 mm. See Ridge and Hip: Short Trim Installation and Ridge and Hip: Long Trim Installation. Gable Ends 

Tile ends are turned up a minimum of 40 mm and installed against a batten that will be covered by a barge cover or under a metal fascia. If a hidden gutter is used, tile edges should be turned down into the gutter by a minimum of 20 mm.







 Flashing Metal Tile to Wall 

The wall cladding flashings must be positioned before the tiles and must be designed so that the turned up tile can be inserted behind the flashing.
All preparatory work of under-flashing, fixing of eaves, gutters and valley gutters must be completed, and all tiling battens must be in place before laying tiles.




 Wall To Roof Junctions 

Flashings at the ends of roofs, where the roof does not end past the wall require a stop-end flashing that ensures water is directed into the gutter. Sufficient material should be left standing out from the wall so that cladding installers can ensure a weatherproof finish. Penetrations 

Tiles cut for penetrations through the roof should be provided with up-stands and over-flashed for drainage from above without restricting the water flow.

The flashing should finish 15 mm beyond the tile head lap above the penetration and should be wide enough to cover the nearest tile rib or up-stand. When the construction is solid masonry or brickwork, and flashings cannot be installed under the wall cladding, a chase should be cut and an over-flashing installed in the chase to provide weather protection.

15.3.6 Longrun Tiles 

A long-run tile is a hybrid roof cladding providing the appearance of pressed metal tile with the fixing attributes of long-run profiled metal cladding.

The minimum pitch is 8˚, and underlay and battens are fixed in the same manner as for pressed metal tiles.

The module or step size of the profile can be adjusted, and the pitch of the tile can be varied to suit any batten spacing on an existing roof or to alter the roof appearance.

Maximum sheet length is 7 m however transverse laps are possible.

The material is pre-painted metallic coated steel with a yield strength of G250 Mpa. It is fixed with nails or screws at the front of the tile.

Sheets should be back-laid, working from right to left which prevents creep at the gutter line due to the back-step in the underlap of the profile.

Longrun tile can be curved to a 250 mm radius.




15.3.7 Sitework 

The requirements of 13 Site Practice also apply to the installation of metal tiles. In addition all gutters, valleys, roof channels and the roof should be left clean and free from debris on completion of the work.


15.3.8 Laying Metal Tiles 

The roofing supervisor will establish when the roof should be installed after all sub-trade work has been completed.

All preparatory work of under-flashing, fixing of eaves, gutters and valley gutters must be completed, and all tiling battens must be in place before laying tiles.

If substantial work, such as texturing walls, is to be carried out on a wall above or adjacent to where metal tiles are to be laid, they should be installed after such work has been completed.

Tiles should be inspected and selected, as tiles of a different colour match should not be installed on the same plane of a roof. If more than one pallet of tiles is required for one job, the colour uniformity should be checked.

Tiles damaged during installation must be removed and replaced, and any deformed tiles or tiles with surface damage must be rejected.

Tiles should be laid from the ridge down to avoid unnecessary traffic and can be laid broken bond or straight down the roof.

The eave gutter tiles should project over the edge of the fascia to ensure that water discharges directly into the gutter system and tiles should be laid so they prevent any water penetrating into the roof cavity.

Before tiles are laid, the direction of lay should be determined by:

  • Taking into account whether the profile can be laid only one way or both ways;
  • Appearance, so that laps face away from the line of sight;
  • Allowing for prevailing weather exposure.

Installation of perimeter tiles (excluding eaves tiles) can be completed before the main body of tiles are laid.

15.3.9 Workmanship 

Graphite pencils must not be used to mark AZ coated steel products as carbon can cause premature corrosion failure of the coating.
Finishing of tile cuts and bends must leave straight lines up the roof section, to provide a true line for flashings.
When cutting tiles for their installation at ridges, hips, valleys and barges, avoid damage to the surface finish by using a guillotine or metal shears. When cutting the tile lengthwise, it must be bent before cutting to reduce the amount of distortion that occurs as the profile is flattened during bending.
Tiles turned up and down for ridges, hips, valleys and barges must be bent using a bender specifically designed for this purpose. Tiles must be turned up at ridges, hips and barges by a minimum of 40 mm, and down into the valleys to a minimum of 5 mm from the valley floor.

15.4 Standing Seam Cladding 


Secret fixed roof and wall cladding is a type of roof or wall cladding that can be divided into two main types:

  • Self-supporting cladding, and
  • fully supported cladding

Both types are installed without visible fixings that penetrate the cladding and have provision for expansion due to the design of their clipping system. The advantage of secret fixed roof and wall cladding is that longer lengths can be used than with pierced fixed cladding and there are no exposed fixings.



15.4.1 Self-Supporting Cladding 

Self-supporting cladding is roll-formed with different means of interlocking the adjacent panels. It can be :

  • spring snapped together;
  • rotated through 180°; or
  • machine closed in situ.

Where the required lengths are too long to be easily transported, and the contract warrants it, the roll forming can be done on-site to avoid damage and reduce packaging and transport costs.

Because there are no external fixings, the wind uplift load on the cladding is resisted by:

  • the strength of the profile;
  • the clip;
  • the screws, nails or rivets, and
  • the substrate.

The loads imposed on the cladding are described in section 3.4.

In many cases, the uplift load that can be resisted by these component parts or the re-entrant cladding design is not as great as that for pierced fixed cladding. Designers should be aware of these limitations in high and very high wind design load areas.

The weakest parts of the clipping system are usually the clips or the clip fixing to the substrate, as the clips are secured by using screws, nails or rivets.

Each clip must enable free movement for expansion within the clipping system. Each clip must have a minimum of two fixings, and the pull-out or withdrawal load of each fixing must exceed half that of the wind design load.

The fixings must be suitable for the substrate.

For timber the fixings should be:

  • nails with an enhanced shank of 50 mm long; or
  • 10# x 25mm wafer head screws.

For steel the fixings should be:

  • 10# x 16mm wafer head screws; or
  • 12# hex head screws (where profile provides clearance).

Secret fix clips must not bind the cladding, as this will erode the metal and produce excessive noise. Clips must be fixed at centres determined by the panel width and the wind design load. Additional clips must be used to provide resistance to the high wind load in the peripheral areas of the roof.

Self-supporting secret fixed claddings can be curved over a radius, but as they are asymmetrical profiles, the radii should be shallow to avoid purlin creasing and panning.

Unless expansion provisions are made to positively fix elsewhere, secret-fix sheeting should be fixed at the highest point to avoid creep on steep roof slopes or due to the action of snow.

15.4.2 Fully Supported Roof And Wall Cladding 

Fully supported roof and wall cladding is a secret clip fix type of flat roof or wall panel, which is joined by seaming, welting or clipping and does not have any external through fixings.

Fully supported cladding is described as non-structural because it requires continuous underneath support, as distinct from self-supporting metal cladding which is structural.

Individual sheets are described as bays or panels. They are not intended to support walking loads without a structural deck of timber or rigid insulation beneath them, although some spanning support is offered by the standing seams or batten rolls. Wall details use similar detailing to roof details except that panels are positively fixed at the top.

The metals used for fully supported roof and wall cladding have historically been non-ferrous and have a reputation for providing a trouble and maintenance free roof, often for centuries. The methods used to fix this type of cladding are labour intensive and therefore expensive. However, fully supported cladding is a better option in terms of life cycle cost.

This type of cladding is termed architectural because as vertical cladding or curved roof cladding, it is a dominant feature of the architectural style of the building. Unlike modular profiled metal cladding, the width of the bays can be custom made and they can be tapered or curved.

Because the role of the architect or designer is expected to be more dominant, giving greater attention to detail than with other types of cladding, it is strongly recommended that early liaison occurs with designated or nominated roofing contractors.

Because of the skill required to install this type of roof cladding, the designer is advised to seek out a contractor that specialises in this field and whose tradesmen are capable of installing fully-supported cladding that will last for over 100 years.

It is impossible to detail every junction or option for fully supported cladding in this COP, but it does provide typical details. Types 

There are two types of fully supported cladding:

  • Traditional architectural annealed metal panels limited to 1.8 m in length.
  • Long length strip roof cladding up to 10 m in length.

Both traditional architectural and long length strip-roof-cladding types share the same seaming methods and also many of the same flashing and fixing details. The cover requirements may differ from profiled metal cladding because whereas profiled laps are overlapped, fully supported cladding laps are seamed.

When annealed grades of metal are used in short lengths, the folds can have a generous radius, because the details are hand worked and do not possess the straight lines associated with machine folded or roll formed cladding.

The use of both types of fully supported metal roof cladding without structural ribs gives rise to undulations in the wide flat pan, which are not only to be expected but an architectural feature of fully supported cladding.

A perfectly flat metal surface cannot be obtained when using wide flat panels, and designers should be aware that fully supported roof or wall cladding will reflect light unevenly, particularly when it is new, and it will not change by increasing the thickness of the cladding.

If designer or customer expectations include flat panels without distortion, then narrow pan secret fix profiled and ribbed metal roof cladding should be considered. If wide flat panels for walls or facades without ribs are required, the COP advises using bonded panels.

Most metals used for this type of cladding are non-ferrous and naturally weathering, and acquire a patina over time that enhances the appearance and the durability of cladding.

Zinc and copper can be supplied in a pre-weathered or pre-patinated finish, and this can avoid the discolouration caused during installation and the uneven colouration of individual panels in sheltered areas.

The loadings, installation, performance, maintenance, corrosion, drainage, and site practice sections of this COP are all applicable to fully supported cladding and should be read in conjunction with this section, which contains only specific detailing and reference to fully supported cladding. Traditional Architectural Metal Panels 

Traditional roofing or architectural non-ferrous metal panels have been used in short lengths for many centuries. They are associated with longevity and a distinctive architectural style. Traditional fully supported roof cladding is made from a sheet, whereas long length cladding is made from pre-formed continuous strip.

There are two reasons why traditional roof cladding has been restricted to short lengths:

  1. Until the 1950's continuous strip was not available.
  2. Fixing did not include expansion details.

Annealed metals used in short lengths are now limited to specialised uses — such as turrets, domes or curved structures — requiring a considerable amount of hand working.

The availability of metals in continuous coils has permitted the industry to take advantage of the old technology and apply it to long lengths of fully supported roof and wall cladding. Long Length Strip Roof Cladding 

Long length roof and wall cladding are roll-formed in longer lengths, generally using the same joining, fixing methods, and installation techniques as traditional roofing or architectural metal panels.

Long strip copper roofing systems have been used in the United Kingdom and Europe for over fifty years, and aluminium have been used in NZ for a similar length of time.

The main advantage of the longer lengths of the system is the elimination of cross welts on sloping roofs and of drips on flat roofs, thus effecting reductions in the labour cost of laying short lengths of metal roof cladding.

The length of individual panels is governed by the type of edge seam, the metal, and the provision for metal expansion of the panel. By using expansion clips incorporated in the standing seams, longitudinal movement of the panels is permitted while still providing a secure fixing to the under-structure.

Roll formed tray roofing panels can be varied in their width to suit the architectural design and the wind design load on the building. They can also be supplied with various upstand heights and details including locking edges similar to secret fixed profiles.

Long strip copper roofing can be laid in continuous lengths of up to 10 m long by 500 mm wide compared to the maximum 1.8 m by 600 mm bays used with traditional annealed panels. Where the rafter length is greater than 10 m, either a step or a cross-welt is required, depending on the roof pitch and the wind design load. Types Of Joints 

There are three main systems used for joining fully supported roof cladding which apply to all metals:

The roll cap is a variation of the standing seam because it has two standing seams one on either side of a square or trapezoidal timber batten. The double seam and angle seam has only one seam.

Conical roll and other types of jointing have been used in the past, but the most common systems are outlined below. The thermal movement across the width of metal panels is taken up by the provision of a gap at the base. 
 Standing Seam 

The term 'standing seam' refers to the way the panels are joined in a vertical, or "standing", position. After being laid on the substrate and clipped, it is seamed either by hand or seaming machine.

The minimum pitch of standing seams more than 30 mm in height running from ridge to eaves is 3°. The minimum pitch for standing seams less than 30 mm high is 5°. See 15.4A Jointing a Standing Seam
 Angled Seam 

The angled seam is the same as a standing seam but has only been folded over by  90°, not 180°. It is considered only suitable for walls and pitched roofs, but not for low slope roof cladding in exposed areas.
The angled seam has the advantage of a more dominant and a straighter line, which is obtained by a roll forming machine rather than hand working, and it is used when the aesthetic expectations are high. The angled seam is restricted in snow areas to a roof pitch of more than 25°. Roll Cap 

Roll cap systems are made from materials of a temper suitable for springing or snapping together. There are many variations, but all depend on the interlocking of a cap and the panel. Some panels have interlocking edges and do not need a separate capping.
When using traditional short lengths, adjacent sheets of metal are joined lengthwise using cross welts and drips for the transverse joints. These types of joints allow for expansion.
Ridges and eaves panel fixing details must accommodate the lengthwise expansion movement of the sheeting.





Batten rolls running from ridge to eaves can be used on all roofs were the minimum pitch is 5°. Transverse Laps 

The transverse seams on standing seam roofs with a pitch of less than 20° in areas of high or very high wind design loads, must be soldered or sealed.
A double lock cross welt transverse joint must be used for joints on roofs with pitches of more than 7°, and single lock cross welts must be used on pitches above 25° or on vertical surfaces. The double lock cross welt must be used in all cases where severe weather conditions exist.
The maximum length for roof pitches of less than 30° must be 10 m. Where a roof slope exceeds 10 m, a 50 mm deep step flashing must be placed at regular intervals to provide for panel expansion in the direction of the fall.

The double lock cross welt should be used in all cases where severe weather conditions exist. Where the pitch is below 20°, the edges of the metal forming the double lock cross welt should be soldered or sealed with silicone sealant before closing the welts and seams and folding together.


Cross welts used with standing seams should be staggered in adjoining bays to compensate for the increase in thickness of many-layered metal, but batten roll joints from ridge to eaves may be used in a continuous line across a roof.

Although a long strip roof can be laid entirely using conventional hand tools, power or hand operated machines are used on long panels to save time.

All joints in weathering details for penetrations, rainwater heads, stop ends, and expansion flashings in sheet copper should be sealed by brazing with silver solder. In zinc, all joints should be sealed using lead/tin soldering. All metals should be mechanically locked before sealing.

All transverse and longitudinal joints on fully supported metal roof and wall cladding must only be welted, lock seamed or capped, and must not be joined solely by soft soldering, welding or brazing.

Where the direction of fall is diagonal to the standing seam and welts, the laying direction of the bays must be away from the flow.

Where rainwater will drain to one side of the bays, high-velocity streams of water flowing down the seams and welts should be directed away from the seamed side of the panel.

Light gauge wide pan widths should be avoided because they give rise to sheet drumming and consequential fatigue.


15.4.3 Standing Seam Materials 


Metals used in traditional architectural panels and used as fully supported cladding include lead, annealed copper, zinc and aluminium.

Metals used in long length architectural panels, however, generally use a harder temper or alloy and include copper, zinc alloyed with titanium/copper, aluminium, stainless steel, and plain and pre-painted AZ coated steel.

The metals described in 15.4.3 Standing Seam Materials are suitable for long length fully supported cladding.

Copper, aluminium and stainless steel can be supplied with an embossed surface finish, which not only reduces glare but can also provide additional strength. Copper 

Roof cladding, gutters, and expansion and fixed clips should be made from a minimum of 0.6 mm half-hard temper strip, conforming to the British Standard, BS 2870.

Roll formed panels using secret fix interlocking edges that are made from half-hard temper, should not be silver soldered or brazed, because the heat required will anneal the copper.

When softened areas in half-hard copper can develop differential stress patterns, caused by expansion, which can result in fatigue and eventual failure of the metal.

Where penetration or other flashings require an amount of workability or are to be silver soldered or brazed, they should be made using fully annealed copper sheet or 0. 6 mm thick strip. See 4.16.5 Copper. Zinc 

Zinc roof panels and flashings should have a minimum thickness of 0.7 mm, although heavier gauges are used.

Copper and titanium are alloyed with 99.995% pure zinc to provide additional strength. See 4.16.4 Zinc. Aluminium 


There are many aluminium alloys available for use in roof cladding, and roll formed panels can be made from soft, 1/2 hard or 3/4 hard tempers with a minimum thickness of 0.7 mm. See 4.16.3 Aluminium

Pure aluminium strip (99%), known as 'dead soft', is used for flashings in widths between 150 mm and 600 mm in thicknesses of 0.30 mm, 0.45 mm, 0.55 mm, and 0.70 mm. Stainless Steel 

Stainless steel has a higher strength than most other metals and can be used in a lighter gauge or thickness. It is compatible with copper but should be used with caution with other metals. See 4.9.4 Compatibility Table. Coated Steel 


Metallic and organic coated steels can also be used for fully supported roof and wall cladding. They require the same treatment as self-supporting roof and wall cladding and the same design criteria as for other metals. See Metallic Coatings and 4.17 Organic Coating.


15.4.4 Loadings 

The uplift forces on fully supported roof cladding are transferred through the building through the clips and fasteners to the substrate.

The performance criterion is the number of clips or fasteners per square metre, which can be varied by the spacing of the clips or the width of the bays. The withdrawal load of the fasteners depends on the metal, shank diameter, shank type, penetration depth, and the type and thickness of the substrate.

The design load capacity of a clip can depend on the material of the clip and the thickness of the substrate.

The clips and fasteners should be able to withstand the wind design load, measured in kilonewton (kN), which is derived from the square measure of kilopascal (kP).

Maximum clip centres for different wind loads shall be derived 15.4.4A Load/Clip Spacing, after making provision for local pressure factors.


    To improve the uplift resistance of fully supported roof cladding, the design options are:

    • reducing the width of the end bays;
    • increasing the metal thickness; and
    • placing the clips closer together.

    The clip spacing is determined by the wind design load, the thickness, type of substrate and the holding strength of the nails or screws. To comply with the wind design load criteria, the withdrawal load of the clip/nail assembly should be known for the thickness and type of substrate.

    Gable or verge panels must be wider than 400 mm, and the clips must be fixed closer together on the edges of all roofs in high wind design load areas.
    Unlike profiled metal cladding, the point load imposed on fully supported cladding is supported by the substrate.


    Smooth shank nails must not be used for fixing clips as they do not comply with the loads given in 15.4.4A Load/Clip Spacing
    Hand or gun-driven screws both provide better performance and are the preferred fixing. The depth of penetration is a major performance factor when considering the wind design load.
    Ideally, clips should be positioned to coincide with sarking support positions. Substrate 

    When plywood substrate is used beneath fully supported roof cladding, it should be smooth and dimensionally stable, with a moisture content of less than 18% and made windtight. All screws should be countersunk to prevent damage to the metal cladding.

    Plywood with a minimum thickness of 12 mm should be fixed to the framing at 600 mm centres, with 40 mm x 8# countersunk screws at 150 mm centres around the panel edges and 200 mm centres on the intermediate supports. The fasteners should not be closer than 10 mm to the edges.

    Although 17.5 mm plywood will span 1200 mm, the length of the fasteners should be increased proportionately.

    A 3 mm expansion gap should be provided between sheets and a nail or screw can be placed in the gap and be used as a spacer for this purpose. All joints should be staggered and taped over before placing the underlay.

    Framing centres should be designed to withstand the increased loads at the periphery of the building.


    Ventilation must be provided for all fully supported roof designs using plywood substrate. See 10.10 Ventilation Pathways.
    CCA treated plywood must not be used under zinc, aluminium, metallic coated or prepainted steel cladding without an underlay complying with 11.5.1A Underlay Suitability or without being separated by an underlayment. Provision must be made for adequate ventilation under the sarking.
    Where the design wind load is higher than 1.5kPa, the minimum fixing centres for 12 mm ply substrate must be 400 mm. Fasteners 

    For specification of clips and cleats see 8.7.3 Secret Fixing Clips
  Zinc or Aluminium

    Nails: stainless steel or hot dipped galvanised enhanced shank nails 25 mm long.

    Screws: stainless steel or hot dipped galvanised countersunk 25 mm long x 8#.



    Nails: copper or stainless steel 25 mm long x 2.6 mm barbed shank flatheads.

    Screws: Stainless steel countersunk 25 mm long x 8#.


    Two types of clips are used:

    • fixed clips; and
    • expansion clips.



    Standing seams up to 3 m long may be secured entirely with fixed clips, but for longer lengths than 3 m, expansion clips should be located above or below the fixed clips to allow for longitudinal movement of the panels.

    Fixed clips should be positioned at centres dependent on the design wind load. See 15.4.4A Load/Clip Spacing.

    The position of the fixed clips depends on the roof pitch. On a pitch of more than 30°, the clips should be placed at the top of the slope.



    15.4.5 Underlay 

    All fully supported metal roofs must have an absorbent and permeable underlay to absorb condensation. Underlay must be laid as detailed in 10.11 Underlay and must be covered on the same day.

    The permeable, absorptive felt or paper underlay should be laid before starting any metal work, and it should be of a type that will not adhere to the metal cladding under temperature changes

    The underlay :

    • allows the passage of water vapour;
    • lessens the possibility of abrasion between the metal and the decking;
    • absorbs condensation;
    • deadens the sound of wind and rain; and
    • separates metal cladding from timber treated with copper preservative.

    15.4.6 Ventilation 

    All fully supported metal roofs must have provision for ventilation of the timber substrate to allow dissipation of condensation.
    Copper is not corroded by retained moisture, but most other metals can suffer degradation from continued exposure to moisture. Zinc is particularly prone to corrosion, but zinc coil is available with a high-build lacquer or specially treated underside to avoid the effects of retained moisture. Where the design is likely to cause continued moisture or cannot provide sufficient ventilation, enhanced underside treatments should be considered for zinc.

    The best provision is always to provide sufficient ventilation at the eaves and ridge, and the minimum of a half an air change per hour to ensure that any condensation is not retained. Proprietary vents made from aluminium or polyethylene can also be used at one per 50m2. These should be placed over a purpose made hole or at the intersections of the 3mm gap between the plywood sheets. See 10.10 Ventilation Pathways.

    15.4.7 Drainage Valleys 

    Fully supported valley gutters should comply with 5.4 Valleys.

    Where a valley is formed between two roof slopes, a separate valley gutter welted to the roof sheeting should be used.

    Jointing between the valley gutter and roof sheeting can be carried out by two methods:


    Valleys should be secured using clips with a minimum of two fasteners, installed parallel to the valley, and be formed from at least the same gauge metal as is the valley metal flashing.

    Securing clips with two fasteners side by side holds the clips in place more securely than using one fastener per clip; with only one fastener, cyclical thermal movement of the valley metal will loosen the fastener, and the valley can bind against the misaligned clips.

    The back tab of a clip should be bent over the fastener heads, and the tab flattened, to keep the fasteners from backing out and from damaging the underside of the metal roof panel.

    Because valleys attached with clips can move within the clips due to thermal expansion and contraction and slip downslope with time, the head of the valley should be securely attached to the substrate. A raised centre within the valley flashing allows for some expansion and prevents water flow running across the valley from one side to the other. See Re-entrant Fold.

    Where a valley drains from a dormer roof and the capacity of the panel or bay does not equal the discharge, it must be spread over two or more bays. See 9.9 Dormer Junctions.

    15.4.8 Facade Cladding 

    Fully-supported facade or wall cladding is used for architectural effect. The width of the panel and the metal thickness can be different from those used for roof cladding. As flat panels do not have a perfectly flat surface, and to improve its visual effect, the maximum panel width should be restricted to 500 mm, and a maximum of 400 mm for panel lengths over 5 m.

    The substrate should be true and in line. Any defect will show and care in seaming is necessary, particularly at the clip positions. To avoid large flat areas, panels can be divided into smaller lengths by single welts, by varying the length or using a diagonal pattern. New panels require precise and clean preparation of the individual components by skilled tradesmen before completing the patination.

    Special care is needed for the storage of the panels, flashings, and components to avoid dirt and staining.


    15.4.9 Edge Finishes 

    Because the standing seam or the batten roll should terminate at the peripheral areas on the roof, this detailing will be determined by the type of intersection.

    The three considerations are:

    • Weathering.
    • Expansion.
    • Appearance.
    All flashing intersections must be made weatherproof without primary reliance on sealants. Provision must be made for expansion in two directions; acceptable joints are shown in the drawings shown in 11.8.


    15.4.9A Standing Seam Edges

    Three stages in preparing standing seam for cross welt at drip, ridge, apron or junction to valley gutter.


    A double standing seam can be turned down through 90°, 150 mm from the eaves, with the folded side uppermost, and the end of the turned down standing seam folded into a cleat, drip or valley.

    When the sheet is engaged into the folded edge at the stepped fall, an allowance should be made to allow for thermal expansion.

    The turned down edge of the bay should not be able to disengage itself from the eaves flashing during thermal expansion, and there should be sufficient room to allow for free contraction of the pan or bay.

    The double seam does not need to be folded over in roofs with pitches greater than 30° as the eaves flashing will prevent any ingress of moisture. The double seam is cut at the eaves, and only the end of the sheet is engaged in the eaves flashing.
    The double standing seam with a splayed or angled lower end is the most demanding end detail, but it is the most visually acceptable.


  Ridge And Hip 

    The method that is used to finish the ridge and a double standing seam depends on whether the type of ridge detail is vented, has a separate ridging, is welted, and whether it is a standing seam or a roll.

    Where the panel passes over the ridge or hip of a roof, a roll not less than 38 mm higher than the intersecting rolls or standing seams should be provided. The ridge roll should be undercut to accommodate thermal movement of the panels.

    An alternative edge finish is to flatten the seam similar to that shown in 15.4.9A Standing Seam Edges










  Apron Or Abutment 


    Where the panel terminates at a wall, there are many different details some of which are similar to those required at the ridge.


    Aprons and flashings to walls and upstands should consist of an independent, preformed strip of metal of not more than 1.8 m in length, welted to the roof sheet or cover flashed to give a minimum 100 mm cover to the vertical upstand.

    Where a standing seam meets an abutment, the standing seam can be finished as for profiled metal roof cladding with an apron or the end of the seam can be flattened to facilitate folding the metal to form the upstand.

    At the highest point of the roll, where it meets an abutment, the sheet is dog-eared to form a corner, and the upstands are welted to the capping and cover flashing. See Standing Seam Abutment.

    Where an apron abuts a block or brick wall, the cover flashing should be folded a minimum of 25 mm into the wall chase with a 10 mm hook wedged into the chase and pointed with a flexible sealant or cement. All free edges should be stiffened as described in Flashings and when retained within a cleat the edge should be free to provide expansion. See 8.3.2 Flashing Edges.

  Eaves And Verge 

    Joints at eaves and verge edges should provide a secure, wind tight termination for the roof, but be capable of accommodating the thermal movement of the panels without overstressing the metal.

    Expansion provision must be made at eaves and verge edges and at the joints.






    Penetration flashings for fully supported metal roof cladding must be installed by the roofing contractor only, and other trades must not cut any hole in fully supported metal roof or wall cladding.

    Penetration flashings used in conjunction with fully supported metal roof cladding require specialist detailing. The details for weathering penetrations in fully supported roof cladding that are included in this section should be read in conjunction with section 9 External Moisture Penetrations

    The back curb of the flashing upslope from the penetration should be installed under the roof panels, and the front apron of the flashing should be installed over the roof panels.





    The designer is responsible for coordinating the penetration location to be sure that a penetration will not coincide with the panel seams.

    When the penetration is less than 50% of the width of a panel, the hole can be weathered by using a fabricated flashing made by forming an upstand by soldering, welding or sealing.

    Small pipe penetrations that can be installed within the width of the individual roof panel can be weathered using an EPDM proprietary flashing as described in 9.5 Boot Flashings These are not the preferred option as the expected life of these flashings is unlikely to equal that of non-ferrous fully supported roof cladding. Shop fabricated flashings may require a conical metal rain collar or a 'Chinese hat' to provide sufficient movement if the pipe is sleeved or insulated.

    Large penetrations are more complex and require additional considerations during design and installation.

    Regardless of the penetration size, weatherproofing should be achieved without relying solely on sealant and independent movement of panel and penetration should be allowed for.

    When the penetration width is over 600 mm the panel ribs should be stopped short of the upslope face of the curb, so that water can flow past the ends of the ribs and not be trapped against the curb.

    Large penetrations that require flashing through the panel ribs and are over 600 mm wide should be factory manufactured to a cricket design as described in section 15.8.

    Flues should be terminated at a sufficient height above a metal roof and discharged in such a manner as to ensure that concentrated flue gases do not come in contact with the cladding.
    Dormer windows, chimneys, vents and other penetrations projecting through the roof can impede drainage and require special design. (9.9 Dormer Junctions)
    The majority of flashings are made from fully annealed or dead soft metal, but where rigidity or a straight line is required, only half-hard grades of material should be used.


    All capping details should allow for expansion and be the same as those detailed in 8.4.3 Parapet Cappings
    Cappings can be welted to the upstands of panels instead of using through fixings.


    15.4.10 Durability 

    Corrosion can be caused by using dissimilar metals in contact with, or run-off from, other roof cladding materials.

    Designers and tradespeople should be aware of the electrolytic corrosion that can take place when small particles of metal are deposited on another metal, and when the same tools are used with a variety of metals. See 4.9 Compatibility.

    For maximum durability, no water should be allowed to penetrate between stacked panels, strips, profiled sheets or coils during storage and transportation. In high humidity with the simultaneous exclusion of air, white rust will develop on the surface of zinc and zinc coated cladding, and aluminium and copper will also suffer permanent staining. All metals in storage should be kept dry. See 13.4 Acceptance Of Materials.

  Patina Formation 

    Metals and metal alloys used for the fabrication of architectural roof panels and accessories are often those that are naturally weathering and whose surfaces develop a layer of protection upon exposure to the elements. Aluminium, copper, lead, stainless steel, and zinc are all naturally weathering.

    A naturally weathering metal forms its own protective layer by oxidation, sufficient to withstand environmental exposures and to develop oxidation layers that are durable and well-bonded to the base metal, with minimum porosity and minimum solubility in water. This weathering and subsequent oxidation can result in a different colour and appearance as well as protecting the metal.

  Copper Patina 

    Upon exposure to the atmosphere, copper develops a protective film called patina, and its composition depends on varying regional atmospheric conditions.

    In industrial and urban atmospheres it consists mainly of basic copper sulphate, and in non-urban environments it consists of basic copper carbonate. These copper salts have chemical compositions similar to those found in natural minerals, and once the patina has developed, no further copper corrosion occurs under normal conditions, As it is self-healing, any superficial mechanical damage is repaired by the renewed formation of patina.

    The patina, consisting of green copper salts, is often described as verdigris which is inaccurate, as verdigris is caused by the chemical reaction of copper with acetic acid.

    In contrast to copper salts, which form a natural patina, verdigris is water soluble and is visually recognised by its strikingly green colour.

    Atmospheric corrosion of copper occurs at 2-3 µm per year depending on the environment, but this rate is applicable only during the first few years and with time it decreases until it reaches zero after 70 years.

    Copper components exposed to the atmosphere undergo various stages of discolouration from the time of installation to the development of the natural patina. Minor marking will become invisible as copper develops its primary protective film, a uniform brown oxide,  after a few weeks due to the reaction with atmospheric oxygen. The intensity of the brown colouration increases with time until the patina develops as a secondary layer of various shades of green.

    This is caused by various copper salts and depends on prevailing local atmospheric conditions, exposure to moisture and air pollutants, the pitch of copper roof or wall areas, and on time. The composition of the atmosphere dictates the rate of patina development and the following periods are considered normal for the formation of the protective patina film:

    • Moderate — 18 years.
    • Industrial — 10 years.
    • Marine — 5 years.

    In mild environments, it may take over 30 years to turn green and in some dry environments, it may never turn colour.

    Strength properties and the degree of purity of the copper do not affect the rate of patina formation.

    In some locations or positions, the slope of the roof, or vertical surfaces or soffits, can affect the development of the patina to the degree that copper may never turn green.

    Copper can be pre-patinated or patinated after installation, and these field methods may provide rapid patination, but the resulting colour can vary significantly.

    Patination can be affected by any streaking, marking, or soiled areas or by perspiration caused by handling, which can be avoided by the use of cotton gloves during installation.

    Water run-off from copper can visibly stain light-coloured building materials, such as concrete, brick and stone.

  Zinc Patination 

    The chemical process which results in the formation of the protective film on the surface of zinc has several stages and may take a long time to develop, depending on the season, weather and other factors.

    During this transitional phase, the surface appears to be irregular due to light reflection. As patination progresses these reflections will disappear; the greyish blue protective film will become denser and the colour more uniform. Patination can be artificially accelerated and Titanium Zinc can be supplied pre-weathered to prevent any difference in appearance of adjacent panels.

    Unwashed areas of zinc and aluminium cladding can show an uneven and patchy surface film when they are in an aggressive environment. Maintenance is required as for other metals. See  16 Maintenance .

    15.5 Insulated Panels 

    15.5.1 Design 

    The use of double skin composite or insulated panels for roof and wall cladding requires the same or similar detailing for flashings, penetrations and design considerations as those for single skin roof and wall cladding described in this Code of Practice. Reference should be made to the relevant section when designing insulated panel systems, as this section only describes specific differences.

    Because insulated roof and wall panels are specialised proprietary systems, few specific details are discussed. However, the principles of water shedding, fastening, and maintenance described in this COP are all applicable.

    Composite or insulated panels are factory made laminated products, using different core materials permanently bonded by adhesive or foaming to act as a single structural element.

    Insulated or sandwich panels have metal facings on both sides; the space between them filled with an insulating core which is permanently bonded to both surfaces.

    Three types of sheeting are used on insulated panels.

    The manufacturing process for bonded panels consists of roll forming the flat or profiled sheeting, followed by the adhesion of the insulation core to both surfaces or skins.

    There are three methods to do this :

    • Continuous metal panel production by bonding panels of insulation to metal skins.
    • Individual panel production.
    • Continuous metal panel production by foaming.

    Site assembled, or built-up systems are also known as composite panels and are of two main types.

    • Two profiled sheets have rigid insulation boards adhered to their troughs, without metal spacers.
    • The sheeting is mechanically fixed on both sides to a structural girt. The girt can form a thermal bridge unless spaced away from the structure. This type of built-up system commonly uses fibre insulation.

    Bonded composite panels develop their strength from the sandwich of skins and insulation, and are made with a tongue and groove side lap detail that incorporates concealed fasteners.

    Flat continuously produced panels suffer minor undulations in the metal skins that arise from built-in tensions in the metal coil and introduced during panel manufacture. Panning can be minimised by using an embossed or matt finish or forming minor ribs or swages on the flat face of the panel.


    15.5.2 Materials 

    The facings or skins of composite panels can be metallic coated, or pre-painted steel or aluminium and are either profiled or flat on either or both sides. The internal skin is also known as the liner skin or sheeting.

    The metal facing or skin is commonly made from grade G300 steel of 0.40 – 0.63 BMT thickness, with pre-painted organic finish over a metallic coating of ZM 275.

    Aluminium facings are used in very humid conditions or a severe marine environment and can be supplied with a mill surface, embossed surface, or they can be pre-painted.

    15.5.3 Insulation Core 

    The bonded insulation core material contributes to the panel strength by providing most of the resistance to shear forces, and the depth of the core determines the panel's resistance to deflection.

    The core can be made from different types of material all with different insulating values, fire ratings, and strengths. The most common are EPS Expanded Polystyrene, PIR Polyisocyanurate, and PPS Phenolic/Polystyrene.

    Expanded polystyrene is used for flat factory bonded panels and can be shaped to the profile of the top skin.

    The insulation thickness of a profiled roof panel varies from 30 mm – 300 mm. To achieve the same insulating value as a flat panel, the profiled roof panel needs to be thicker.

    Dense rigid mineral-fibre insulation may be selected for applications where fire resistance or acoustic insulation properties are considered to be most important.

    Built up or composite panels insulated with extruded closed cell polystyrene or fibre insulation material may need to be of a different thickness to achieve the same insulation value.


    15.5.4 Structural 


    Composite panels are integral units in which the insulation layer together with the two metal skins act as a beam to resist wind and point loads.
    The synergy acquired by the combined strength and stiffness of the metal and insulation core is far greater than the sum of the component parts and large spans are possible. The strength and stiffness of insulated panels are determined by both the metal and its thickness, and the core material and its thickness. Using profiled sheeting for one or both faces can further increase the strength, and increasing the thickness of the core permits using larger spans under the same loading conditions.

    The number and strength of the fasteners under wind suction loads can limit the maximum purlin spacing. If roof-lights are required, the maximum purlin spacing will be limited by the strength of the roof-light sheeting. Polycarbonate or G.R.P. barrel vault roof-lighting may avoid this restriction.

    Insulated panels, unlike single skin profiles, can support normal foot traffic without damage, because the foam core provides continuous support to the external sheeting to resist deformation and indentation.

    All persons walking on the cladding should wear footwear suitable to comply with the safety requirements in 13 Safety, and also to avoid marking or scratching the surface coatings.

    Structural bonded composite roof panels contribute to site safety because, once fixed, they provide a safe working platform. Fixed panels are fully trafficable at all practical spans, foot traffic on unfixed panels, however, should be restricted to the roof panel erectors.

  Supporting Structure 

    Composite panels are supported on purlins or girts, which should be accurately erected to a maximum tolerance of 3 mm and L/600; due to their inherent stiffness, insulated panels do not have the flexibility to follow uneven structures.


    Where composite roof panels are required to have end-lap joints, the external sheets are overlapped, and the joint in the lining and insulation is a butt joint. As both sides of the joint require support, and the fasteners are at one side of the joint, the purlins should be wide enough to provide this support.

    All transverse laps should be fixed and sealed to prevent the passage of air, water or water vapour.

    If composite panels are expected to provide restraint to the purlin or girt flanges, through fixing with oversized holes is required which allows panels to slide under thermal movement, as clips do not provide sufficient restraint. Where fixings are widely spaced panels may not effectively restrain the purlin or girt flange.

    Composite panels should not be used in lieu of sag bars as their function is to hold the purlins or girts in their correct location while the panels are erected.

    Composite panels have a structural integrity which single skin profiled sheets do not possess, and can accommodate penetration openings of 350 mm diameter or 300 mm square without the need for additional structural supports or trimmers.

    Where larger holes are required trimmers should be in place before the erection of the panels.


    15.5.5 Thermal 

    Thermal bowing can occur when the two skins are at significantly different temperatures such as north facing walls, e.g., when a coolroom roof panel is in direct sunshine. The effect is accentuated when the external surface is a dark colour and is more severe for aluminium facings.

    A method of limiting the thermal bow is to make stress relief cuts in the panels as follows.

    1. When a panel is restrained at three or more points, a cut completely severing the cold skin may be required at the intermediate point.
    2. When a panel is attached along its edge, a partial stress relief cut may be required.

    The through fasteners or fixing clips are cold bridges, but it has been shown that these are unlikely to increase the U-value by more than 1 –2 %.

    A joint may be required when the roof panel is longer than 15 m. It can be a sealed lap joint with provision for expansion, or a stepped or waterfall detail. See Step Apron.


    Most panels have a fire resistance when used as a non-loading panel, and the cores are made from insulating foam incorporating fire retardant materials. Fire regulations aim at reducing the risk of death or injury to occupants, the public and the fire service, and it is achieved by the selection of materials which behave in a predictable manner.

    Steel and aluminium liners achieve classifications for combustibility, ignitability, and surface spread of flame; for fire resistant wall construction, steel-skinned composite panels must be used because the melting point of aluminium is too low.

    Polystyrene cores are not easily ignited behind the metal skins but can melt and flow out of the panel. Such cores must not be used for internal partitions or ceilings, where there is a high fire risk. Polystyrene cored panels must be isolated and protected from radiation from hot flues.

    Once a fire has started within the foam core, fire services are unable to trace or extinguish it and the building should be regarded as unsafe.

    Because nylon bolts may jeopardise the integrity of the building during a fire, other mechanical connections should be used if the building is required to have a fire rating or is considered a likely fire risk.

    N.B. Fire ratings are available for non-load bearing applications.

    Aluminium-skinned composite panels, nylon bolts or polystyrene cores must not be used where the building is required to have a fire rating or is considered a likely fire risk.


    15.5.6 Condensation 

    Metal facings are effectively impervious to penetration by vapour, while polystyrene insulation has a closed cell structure which does not permit significant transmission of vapour. Interstitial condensation cannot occur without the presence of vapour in the insulation; to prevent this it is necessary to seal all laps and gaps.
    The side-lap joints require sealing to prevent condensation on the overlapping edge of the external sheeting. Transverse laps, joints and ridges should also be fastened and sealed.

    When composite panels are used as cold store insulation a complete and continuous vapour barrier is essential to prevent inward moisture vapour pressure. Any discontinuity will result in a build-up of ice which can destroy the panel.


    15.5.7 Acoustic 

    Acoustic insulation properties are related to cladding mass, and as composite panels are relatively light, they do not have inherently good acoustic insulation properties. They can be installed with sealed joints to reduce airborne sound and can perform as well as some built-up systems.

    Acoustic absorption depends on the nature of the lining. Flat metal linings absorb very little acoustic energy, and it may be necessary to install additional acoustic lining systems.


    15.5.8 Fixing 

    Composite roof panels with trapezoidal ribs are through-fixed with a load spreading washer on the rib and require sealing at the side-laps. Flat concealed fix composite panels require more complex jointing systems.

    Profiled cladding side laps require stitching at the rib at 500 mm centres with a strip sealant of approximately 9 mm x 3 mm or similar. See 8.5.2 Secondary Fasteners.

    The through fixings may also be pan fixed or located on a mini-rib or swage within the trough, but purpose-designed fasteners are required to maintain the weather seal between the metal skin and the washer. Pan fasteners should not be over-tightened as this causes shallow dents around the fastener head and washer. The washer should have a minimum diameter of 25 mm to provide good pull-over strength.

    All fixings must have a pullout strength and frequency to equal the wind design load. See 3.12 Fastener Performance.
    The maximum practical length of panels is restricted to approximately 25 m, because the weight of greater lengths may present handling problems. Where a transverse joint is required, there are two options.
    1. At end-laps, the lining and insulation is butt jointed over the purlin, and a 150 mm overlap is formed in the external weather skin only using two lines of sealant. The sealant should be silicone or preformed strips and positioned at the top and bottom of the lap. To provide a secure seal with flat or wide pan profiles, additional sealed rivets or stitching screws are required through the top skins only. This detail is only suitable where the roof pitch is more than 10° and where the maximum length is less than 1 5 m.
    2. Where the pitch is below 10° or the length is more than 15 m, a stepped or waterfall joint is required. See Step Apron.

    The bottom skins of composite panels have an integral side lap with a re-entrant sealing space which acts as a vapour control, but in high-risk applications such as food processing buildings, textile mills, and indoor swimming pools an additional sealer strip is required at the lining. Concealed fix systems may be used on very low pitches to conceal the fasteners from the weather and keep it out of sight.

    15.5.9 Flashings 

    Flashings detailing is similar to that used with single skin roof and wall cladding or built-up systems, but there are minor differences that may influence design decisions and special requirements that should be addressed.

    The panels at the ridge should be sealed and the lining closed with a metal trim mounted on the ridge purlins. Any gap between the ends of the composite panels should be insulated to eliminate cold spots or cold bridging. They can be sealed using in-situ injected foam or mineral fibre. In high humidity applications the liner trim should be sealed to the panels, and at end-laps or gaps, foam should be injected to provide a vapour tight seal.

    Eaves panels should have the ends turned down to direct water to drip into the gutter, and to have a metal flashing to cover the exposed end of the insulation and metal liner.