COP:flashings; flashing-types

7.4 Flashing Types 

Different types of flashings include:

  • Ridge and Hip.
  • Barge and Verge.
  • Parapet Cappings.
  • Apron.
  • Valley.
  • Curved.

For penetration flashings , including window and door flashings , see 8 Penetrations.

7.4.1 Ridge And Hip 

Ridge and hip roll top flashings are roll-formed as a standard pitch flashing, with or without a soft edge. Because the pitch is not custom made, it can result in visible distortion and stress around the fastening, when used on pitches steeper than 15°.
Custom made square top ridging is available for any pitch and width. They are available in lengths of up to 8 m, but recommended single lengths should be limited to 6 m. The roll top or square top of a ridging allows for expansion and strengthens the ridge.

A vee ridge is not able to support walking traffic. However, 0.55 mm steel roll top or square top ridging can be walked on with care.

Vee ridging can be used on:

  • ridge vents;
  • where the cladding length is less than 6 m in length;
  • where the roof pitch is more than 35°; and
  • where an expansion clip fixing is provided.

 

7.4.1.1 Ridge - Hip Intersections 

The transition at the ridge and the apex of a hip require skill to make a neat and weathertight finish. An under-flashing such as soft aluminium, underlay, or butyl membrane is recommended as a secondary means of making this joint waterproof in conjunction with the design of ridge-hip intersection. (See 7.4.1.1A Soaker Ridge Cap)

The transition at the ridge and the apex of a hip must be made weathertight by either:

  • Cutting, lapping and sealing of the intersecting ridge flashings. (See 7.4.1.1A Soaker Ridge Cap)
  • Using a soft aluminium or zinc capping that can be formed to suit different pitches and profiles.
  • Using proprietary pressed three-way roll caps made from coated steel, pre-painted steel, aluminium, or Zinc. (See 7.4.1.1B Three-way Roll Cap) Preformed flashings are only suitable for a narrow range of roof pitches

 

 

7.4.1.1C Roll-top End Cap

The gable end termination of roll ridging must be made vermin proof by either using a separate cap or by cutting the ridging back 25 mm and closing, it as shown in 7.4.1.1C Roll-top End Cap.

An alternative to continuous ridging on ribbed profiled sheets is using individual rib or ridge caps, fitted to each rib after the ribs have been cut and the roof cladding bent over the ridge. Each cap should be accurately fitted and sealed; this method does not allow for free expansion at the ridge of long length roof cladding.

Although there is little run-off at the ridge pressed, one-piece ridge caps, such as Canterbury prickles or shark's teeth, are the preferred caps. All caps rely on sealant to be made watertight.

Rib caps must not be used in Category B in 7.3A Minimum dimension 'C' flashing cover.

 

 

 

7.4.2 Barge And Verge 

 

Barge or verge flashings serve a dual purpose, which is not only to weather the junction of the roof cladding at the barge, but also to hold the roof cladding in place under fluctuating wind suction loads.
Unstiffened roof cladding without barge flashings can fail under high wind load conditions because of the 'peeling' effect, which can lift a roof off. Although the cause may appear to be a single catastrophic moment, it is caused by the incremental failure of the fasteners at the verge.

 

7.4.2.1 Internal Barge Flashing 

A transition flashing must be provided when the roof cladding weathers the barge at an internal angle (see 7.4.2.1A Transition Flashing) .

 

7.4.2.1A Transition Flashing

Spouting has been omitted for clarity. The barge is overlapped by a transition piece, which in turn is overlapped by the higher sheeting. Where the pitch is low, a sloping transition is required to drain the water into the spouting.

 

7.4.2.2 Internal Corners (Ridge - Hip Intersections) 

 

Where a shorter gable meets another with an overhanging eave, the difficulty of access can prevent fixing by normal methods. One solution is to block off this area and treat the internal corner as a penetration. (See 7.4.2.2A Shorter Gable meets Eave Overhang 7.4.2.2B Barge Flashing on an Internal Corner, and 7.4.2.2C Barge Flashing — Ridge Cap)

 

7.4.3 Parapet Cappings 

Cappings or copings are used to cover the top of a parapet wall to protect the wall from the ingress of moisture. Metal cappings are used to cover existing wall materials that are porous, such as concrete block, precast concrete or EIFS (Exterior Insulation Finishing System). Instead of chasing into the wall and using step flashings, the preferred detail is to cover the parapet wall with vertical ribbed metal or other cladding material, used in conjunction with an apron flashing. (See 7.4.4B Vertical Cladding (Parapet Flashing and Detail)

Metal cappings must have a minimum of 50 mm overlap on each vertical face over flat cladding, but where the cladding is not flat, or profiled cladding is used in high or very high wind zones, the vertical cover must be extended. (See 7.3A Minimum dimension 'C' flashing cover.) 

Metal cappings must have a minimum unsealed horizontal lap of 150 mm, or 25 mm minimum sealed lap to provide a weathertight flashing (see 7.3.1A Minimum End Lap of Mating Flashings), and an expansion fixing provision when the length exceeds 12 m (see 6.2.2.3 Expansion Details.)

Capping corners must be sealed, soldered, or welded (depending on the metal used) and expansion joints located at the corners, within 1 m from each direction of the corner measured on the interior side.

The corner of the wall is a fixed point for the capping, and as thermal movement can only occur in one direction away from the corner, an expansion joint should be provided as shown. (See 7.4.3A Parapet Corner Capping)

 

7.4.3A Parapet Corner Capping

width=498 height=261 /> </p>  <p> A slope is required to drain water from the exterior surface and also to drain any condensation from inside the building that would accumulate on the underside of the capping.</p> <p> A continuous timber packer should not be used under the metal capping because it will inhibit ventilation. Filler blocks should not be used for the same reason on vertical profiled metal cladding. Intermittent blocking at 600 mm centres can be provided , but the lap should have support and there should be provision for attachment at 600 mm centres at the drip edges.</p> <p> A building underlay should be used as an isolation sheet for incompatible materials or to act as a slip-sheet for materials with differential movement.</p> <div class=blueBg1> Parapet cappings must have a positive slope of 10° onto the roof side and must have a permeable and absorptive underlay. Synthetic wraps must not be used directly under metal cappings.<p> Parapet cappings that follow the slope of the roof do not require any fall across the capping.</p> </div> <p> Parapet cappings wider than 300 mm can fall both ways with the 10° drainage angle provided to both sides of the capping. A 5 mm gap between any flat wall surface and the capping will allow some air movement and reduce condensation. A gap is also required for aesthetic reasons to avoid marking or staining, and to allow condensation to drain.</p> <p> Cappings must not be fixed to the structure through the top of the capping but can be fixed on the vertical leg by one of three alternative methods : <em style=line-height: 19.1999988555908px;> <a  data-cke-saved-href=page159 href=page159> (see drawing 5.3.4. B, C, & D)</a> </em> </p> <p> 1</p> <div class=bodyTextb> <div class=indent> <div style=margin: -30px 0px 0px 40px;> Where a continuous cleat is fastened on the exterior face of the wall with an open hem at the drip for ease of application. After the exterior face of the capping is hooked to the cleat, the capping on the interior side is secured to the parapet with washered fasteners through oversized holes.</div> <p> 2</p> <div style=margin: -30px 0px 0px 40px;> Where intermittent clips are fastened to the exterior face of the wall at 600 mm centres.<br /> <br /> After the exterior face of the capping is hooked to the clip, the interior face on the roof cladding side is fastened to the parapet with screws with sealing washers, through oversized holes.<p> All cleats and clips should be accurately aligned and clinched after fixing, while still allowing for expansion movement without chatter or vibration.</p> </div> <p> 3</p> <div style=margin: -30px 0px 0px 40px;> Where the capping is fastened to the parapet on both sides with screws with sealing washers, through oversized holes.<p> If a hem is used on a capping made from metallic-coated or pre-painted steel the hem radius should comply with <em> <a  data-cke-saved-href=page49 href=page49> section 2.3.4.</a> </em> </p> </div> </div> </div>  <p> <img  data-cke-saved-src=/sites/default/files/cop_22images/diag_5.3.4b.gif src=/sites/default/files/cop_22images/diag_5.3.4b.gif alt=

A slope is required to drain water from the exterior surface and also to drain any condensation from the inside of the building that would accumulate on the underside of the capping. A continuous timber packer should not be used under the metal capping because it will inhibit ventilation. Filler blocks present the same problem on vertical profiled metal cladding.

Intermittent blocking can be provided at 600mm centres, but the lap should have support, and there should be provision for attachment at 600mm centres at the drip edges. A building underlay should be used as an isolation sheet for incompatible materials or to act as a slip-sheet for materials with differential movement. 

Parapet cappings must have a positive slope of 10˚ onto the roof side and must have a permeable and absorptive underlay. Synthetic wraps must not be used directly under metal cappings. Parapet cappings that follow the slope of the roof do not require any fall across the capping.

Parapet cappings wider than 300mm can fall both ways with the 10˚ drainage angle provided on both sides. A 5mm gap between any flat wall surface and the capping will allow some air movement and reduce
condensation. A gap is also required to avoid marking or staining, and it allows condensation to drain.

Cappings must not be fixed to the structure through the top of the capping, but can be fixed on the vertical leg by one of three alternative methods. (see drawing 5.3.4. B, C, & D).

  1. Where a continuous cleat is fastened on the exterior face of the wall with an open hem at the drip for ease of application.
    After the exterior face of the capping is hooked to the cleat, the capping on the interior side is secured to the parapet using washered fasteners through oversized holes.
  2. Where intermittent clips are fastened to the exterior face of the wall at 600mm centres.
    All cleats and clips should be accurately aligned and clinched after fixing, while still allowing for expansion without chatter or vibration.
  3. Where the capping is fastened to the parapet on both sides using screws with sealing washers, through oversized holes.

7.4.4 Apron Flashings 

Cladding should not fit tightly onto the horizontal surface of any apron flashing; it will retain moisture and collect dirt and debris. It should have a minimum clearance of 25 mm.

Apron flashings should be in position before any parapet cladding is installed. The vertical leg of apron flashings should be a minimum of 100 mm high and hemmed or hooked, unless this would cause difficulty in fixing. This dimension provides 25 mm clearance between the apron and the cladding; if a hook or hem is not possible, the apron height should be increased by 25 mm.

To avoid capillary action, a break should be made between the capping and the vertical-fixed surface using 'birds beak' or similar break on the flashing edge. No down-turn into the pan of the profile should have a clearance of 2 – 5 mm from the pan. (See 7.2.2B Scribed Flashing) 

Where the finish above the apron is plaster or the durability of the cladding is 50 years, the hidden apron flashing is also required to have a 50-year durability. It can be achieved by using a non-ferrous material for the flashing. Alternatively, a two-piece apron should be used where the over-flashing has a 50-year durability and the apron flashing can be renewed independently. (See 7.4.4F Two-piece Apron.) 

Any stiffening edge should not be turned inwards, as not only will this scratch the cladding when it moves, but it can also be the cause of roof noise.

When the parapet walls will be plastered or when other trades are likely to follow the roof cladding installation, the roof cladding and flashings should be protected from damage. Provision should also be made for working and walking on the roof cladding during this time.

It is the responsibility of the roof fixer to make this requirement known to the contractor, and the COP recommends photographic and documentary evidence to avoid any future claims for damage caused by others.

Where an apron abuts a block, brick or concrete wall without any cladding above it, the apron flashing can be weathered by a step or a continuous chase flashing. These flashings can be made from aluminium, stainless steel or zinc when used with metallic-coated steels, and should extend 25 mm into the wall. They should be hooked or mechanically wedged and should be sealed with a compatible, flexible mortar or sealant. (See .) 7.4.4 Apron Flashings

 

 

 

Waterproofing, release from curing agents or the moisture content of the concrete slab can inhibit adherence of the sealant to the concrete. This area should be primed to ensure the sealant bond.

7.4.4A Chased Apron and 7.4.4C Angle Diverter are not the preferred installation methods for apron flashings. 7.4.4B Vertical Cladding (Parapet Flashing and Detail)shows a better method that provides more positive weathering by covering the wall with vertical metal cladding up to the capping.

Where the roof sheeting stops short and does not extend to the wall, the unsupported apron flashing can have a transverse fall back towards the internal angle of the apron flashing. It is not possible to ensure that all the water discharged from the apron flashing will be collected by the spouting at this junction, unless special provisions are made including:

For clarity, the spouting has been omitted from these drawings. Spouting should be fitted after the wall has been finished and should be 10 mm clear of the wall cladding.

Aprons should be stop-ended and turned down to weather and bird-proof the end of the apron at this junction.

When flashing a cavity parapet, the apron should be in place before the cavity batten as it is not possible to retrofit the apron. The apron material should have a 50-year durability unless the parapet cladding is easy to replace.

When a chase or reglet (7.4.4G Chase-fixed Flashing)  is not provided, a pressure bar flashing can be used to weather an apron flashing into a concrete tilt-up slab wall.

 

One method of obtaining a seal without cutting a chase is to screw-fix a rigid angle to the wall with an EPDM foam or butyl strip behind, as shown in 7.4.4H Pressure Bar with Butyl Backing. This method gives the advantage that the flashing can be easily replaced and it can be the same material as the roof cladding. Take care seal the junction at the chamfered edge of the slabs with a 'make-up' piece of backer rod or something similar.

 

7.4.4.1 Parapet And Apron Capping Terminations 

A parapet as defined and referenced in this Code of Practice is limited to 1 m high. A wall with a parapet higher than 1 m is termed a parapet wall and this area should be added to the catchment area. See 5.3.1 Catchment Area.

All apron and parapet flashings are regarded as being in a 'higher risk' weathertightness area, particularly in Category B areas. See 7.3 Flashing Cover.

The large amount of catchment area from a wide or high wall and the turbulence created at the junctions requires precise detailing to avoid water ingress. See 5.3.1 Catchment Area. This can only be assured by following the better practice flashing details contained in this COP.

Face-sealed parapet claddings require a cavity wall construction.  However, it is not considered necessary for vertical metal cladding with trapezoidal, corrugated or mini-corrugated profiles. These profiles will provide sufficient ventilation to avoid the accumulation of condensation providing the capping details are adhered to.

The sequence of completing these junctions is essential as the cladding should be finished before the spouting or guttering is installed. The gutter or spouting should have a 10 mm clearance from the cladding. Where the apron terminates at the gutter line and the parapet extends beyond it as a firewall, the cladding should be broken at this point to avoid a sealant reliant joint. See 7.4.4.1B Apron End Diverter.

Apron flashings should not be turned up as that not only collects dirt and debris, but causes water turbulence. Aprons should be turned down to birdproof the end of the apron as shown in 7.4.4.1C Parapet Above Apron, 7.4.4.1D Parapet/Apron Ridge Cap7.3.4.1E Corner Abutment and 7.3.4.1F Slip Expansion Joint.

 

 

 

 

There are methods of weathering a junction where an apron flashing meets a ridge.

 

 

 

 

 

 

 

Parapet cappings should have a separate cap at the apex or be joined as shown in 7.4.4.1G Parapet Ridge.

 

 

7.4.4.2 Change Of Pitch 

Differential movement will happen at any change of roof cladding pitch where the sheets are overlapped and butted together. This movement causes noise and deterioration of the coating. A separate apron flashing as shown on drawing 5.3.5.2 is required to prevent that.

A junction flashing must be used where sheeting is cut at a change of pitch. The junction must be hooked and have the minimum coverage as required according to the exposure category in 7.3.1 Flashing Laps. The underlay must overlap the flashing as shown.

 

 

 

7.4.4.3 Step Apron 

A step apron or waterfall flashing must be used where the length of roof cladding is more than can be transported, or exceeds the recommended length for expansion as shown in 6.2.2 Roof Cladding Expansion Provisions.

End lapping of long length cladding is not recommended, because of the inevitable deterioration due to moisture retention in the lap and the expansion requirements.

The designer should allow a minimum 20 mm step in the purlin height to accommodate a step apron, giving a total change of height equal to 20 mm plus the profile height. The purlin height can be adjusted at the purlin cleat or by using a different size purlin. (See 7.4.4.3A Step Apron Details.

The undersheet should be fully stop-ended with a metal flashing closure strip as shown and closed cell filler blocks used on the lower roofs with a pitch of less than 10°, or in areas of very high design wind load.

Minimum fixing requirements are for over-sized holes, and the end spans at the step should be reduced as described in 3.14.2 Sheet Overhang.

 

 

7.4.4.4 Gutter Apron 

 

 

 

Where the ends of roof cladding are exposed to contaminants such as sea salt or industrial pollutants, it is good practice to provide an over flashing which discharges into the gutter or spouting. (See7.4.4.4A Over Flashing.)

  • It gives a measure of protection to the underside of the roof cladding and the underlay.
  • It provides support for the roofing underlay which is subject to damage from wind and UV.
  • When using PVC spouting, there is a gap between the spouting and the fascia caused by the thickness of the brackets. In coastal locations where the ends of roof cladding are exposed, this unwashed area becomes susceptible to corrosion. A gutter apron can minimise this risk.
  • If there is no spouting or it has a low front.
  • In severe environments, wind can drive contaminants up the ribs of exposed ends of roof cladding. Metal scriber flashings or filler blocks can be used to prevent or inhibit ventilation.

The over flashing should extend 50 mm into the gutter, and the underlay finishes on the down-slope of the flashing. If there is no over-flashing to the gutter, the underlay should be extended into the gutter by a minimum of 20 mm.

In some cases, the over flashing becomes a sacrificial flashing which can extend the life of the cladding. In such circumstances, the COP recommends that the flashing is made from aluminium.

7.4.5 Valley Flashings 

 

Valley flashings are centrally folded, sloping internal gutters used where the roof pitch is more than 12°. They are required when the roof cladding changes direction at an internal corner or where a pitched dormer window penetrates the roof structure. (See 5.6 Valley Gutters.)

Valleys should be fixed by clips to allow for longitudinal expansion, and should not be through fixed to the roof cladding.

A valley should be regarded as part of the roof cladding. All vertical valley laps should be sealed to avoid condensation accumulating at the top and to prevent the ingress of water by capillary action at the bottom of the lap.

 

7.4.6 Curved Flashings 

Draped curved and crimped curved metal roof cladding requires curved barge and apron flashings which may not always have an even radius.

The prime purpose of curved flashings is to exclude the weather and to provide structural integrity to the roof cladding. They also have a role in the architectural or aesthetic appearance of the building and help to finish the barge in a visually acceptable manner.

To provide acceptable appearance and weathering, curved flashing measurements should not be taken from drawings, but need site measurement with a template taken from the as-built structure.

Considerable skill and care is necessary to obtain a good fit, particularly at side laps, which should be sealed when they are below the minimum pitch for the profile.

There are three different ways to form curved flashings, all of which require specialist equipment.

  • lock-forming or lock seaming;
  • 'jennying'; or
  • crimping.

Manufacturing curved flashings is a highly skilled operation and should be done in a factory by skilled workmen.

Lock-form roll tooling is not adjustable and can cause micro-cracking on external bends, although that can be minimized by forming the flashing material at a warm temperature.

Roll tooling can damage organic coatings and a stripable film should be used on all pre-coated material to minimise surface damage. Remove the film before fixing the flashing.

7.4.6.1 Lockseamed Flashings 

All lock-seamed flashings should be custom-made to suit the profile shape and the rib distance from the fascia with sufficient downturn on both sides to weather the junction. Lock-seamed flashings are made in two parts, the horizontal (part a) and the vertical (part b), and should be made from 0.55 mm G300 steel, or ductile aluminium or copper.

Edges can be either crimped or lockseamed as shown in these drawings.

 

 

7.4.6.2 Jennied Flashings 

The vertical barge component (part b) can be cut to the curve and edge seamed using a by a Jenny edger, with the horizontal component (part a) hooked and seamed together. (See 12.8 Tools Of The Trade.) 

Shallow curved flashings can be folded straight in one piece and crimped on both edges. Fix the turn down at the curved rib by' mini-crimping or 'gear-crimping'. The Jenny tool can also create a limited curve.

7.4.6.3 Crimped Flashings 

Crimped flashings are suitable for use on radii of more than 2 m, with the crimp spaced and deformed at regularly spaced intervals. A flat strip should be placed on the template and crimped until the strip fits the template.

Because the flashings are seen from much closer, domestic clients may find this type of flashing aesthetically unacceptable.

 

 

 

7.4.7 Soffit Flashings 

Where a soffit and the horizontal or vertical metal wall cladding meet, the junction should be over flashed with an angled flashing which provides the same cover as is required for other flashings. (See 7.3 Flashing Cover.) 

This flashing is an under/over flashing, i.e., it should be installed above the soffit lining and over the outside of the metal cladding.

Where a curved soffit meets a vertical wall, the flashing can be 'gear crimped', crimped as shown or lockseamed. (See 7.4.6.3 Crimped Flashings and 7.4.6.2 Jennied Flashings,)