COP v3.0:maintenance;

16 Maintenance  

Maintenance is defined as 'to keep in good condition or repair', and can be divided into four categories:

  • Normal.
  • Scheduled or Planned.
  • Preventative.
  • Special.


16.1 Improved Durability 

Most people do maintenance retro-actively, they mow lawns, wash the car or remove debris from gutters when they see it needs to be done. While rain washed metal roof surfaces do not generally require maintenance to comply with warranty conditions, it is always good practice to conduct regular inspections for dirt build up or deteriorating components, which can be removed or replaced respectively before they contaminate the body of the roof.  Unwashed areas of roofing and wall cladding do require regular maintenance to comply with warranty conditions.

Section B2 – Durability of the NZBC gives live cycle requirements for materials of 5, 15 or 50 years “subject to normal maintenance”.

In most applications profiled metal cladding and associated materials have a 15 year requirement to comply this clause.  Cladding used as structural bracing, and hidden elements, may require 50 year durability, and exposed spouting and downpipes, 5 years.

The use of pre-coated or pre-finished roof and wall cladding with a minimum 15-year warranty, has led to the belief that no maintenance is required for that period. That is incorrect. The terms of the warranty state that maintenance is required, and the performance of metal claddings is entirely dependent on the environment. See 4.3 Metal Performance.

Individual components of a building system that are difficult to access or replace must either all have the same durability; or must be installed in a manner that permits their replacement without the need to remove building components that have greater durability.
In this context, the performance requirements of the NZBC means there should be no moisture penetration due to product failure. That means fasteners still comply with the NZBC as long they prevent water ingress, despite having deteriorated visually.

Continued maintenance and over-painting will enhance the decorative appearance and extend the lifespan of all roof and wall cladding, and rainwater products.

16.2 Normal Maintenance 

The maintenance described in this section refers to the maintenance of the building envelope; it excludes equipment located on the roof cladding, such as air-conditioning or communications equipment.

Maintenance work and workers must comply with 14.6 Walking On Roofs. Normal maintenance is the work necessary to achieve the claimed or expected product durability. The extent and nature of the maintenance will depend on the material, its position on the building, geographical location and the macro- and micro-environment of the building site.

Section B2—Durability of the NZBC defines 'normal maintenance' as: "work that is generally recognised as being necessary to achieve durability for a given roofing element…."

It is the responsibility of the person specifying the building element to determine normal maintenance requirements.  The specifier should select materials taking into account the accessibility of the building element and the practicality of conducting regular maintenance for areas with restricted access.

Normal Maintenance tasks include:

  • following manufacturers maintenance recommendations;
  • washing down surfaces, particularly exterior building elements, subject to wind driven salt spray;
  • re-coating interior and exterior protective finishes; and
  • replacing sealant in joints.

Compliance with the durability requirements of the COP should not include replacing protective surfaces on roof and wall cladding, and accessories if the products are selected, installed and maintained in accordance with good practice.

It is the responsibility of the person specifying the building product to determine the normal maintenance requirements for the material.

Because of the natural disinclination to carry out maintenance on parts of the building that is not seen or is higher than 3 m, ' normal' maintenance should become 'scheduled', and will require washing as per the schedule in 16.3 Scheduled Maintenance.

16.3 Scheduled Maintenance 

Scheduled maintenance is routine maintenance that is performed at regular intervals.

All roofing and cladding products are subject to the cumulative effects of weather, dust and other deposits. Normal rain washing will remove most accumulated atmospheric contaminants, and little maintenance is required on an exposed well designed and installed roof.

All other areas are regarded as 'unwashed areas', i.e., those areas protected from the direct effect of rain. These include all vertical wall surfaces that are above an angled line drawn at 45° to intersect the edge of the overhang or soffit, the underside of gutters or fascias, and the sheltered areas of garage doors. See 4.10.1 Unwashed Areas

Manual washing is required to prevent the accumulation of dirt, debris or other material not removed by rain. Wall should be washed:
  • every 6 months in severe environments; and
  • every 12 months in moderate environments.

Areas that do not receive adequate or any rain washing such as soffits, wall cladding under eaves, the underside of gutters, fascias, sheltered areas of garage doors, and unwashed roof areas: should be washed:

  • every 3 months for severe environments; and
  • every 6 months for moderate environments.
Scheduled maintenance comprises the inspection, maintenance, and reporting procedures for building elements required to have a compliance schedule in terms of section 44 of the Building Act.
By following those procedures, the building elements are effectively deemed to have a durability for the life of the building, because they are required to perform as designed at all times. The relevant maintenance procedures may include total replacement.

Warranty requirements and durability compliance will only be met if the maintenance requirements specified by the coil coating manufacturer are followed.

16.4 Preventative Maintenance 

Good design can avoid frequent maintenance, but preventative maintenance may provide the most economical solution. This can be achieved by enhancing the product before installation, or by painting metal cladding at nominated intervals.

Where the underside of metal roof cladding is subject to contaminants such as salt at the gutter line, an over-flashing should be inserted between the roof and the gutter to prevent deposits which lead to 'inside out' corrosion. This flashing can become a sacrificial one where dissimilar metals are used for gutters or spouting, and where splashes and contaminants can corrode the roof cladding. See Eaves Flashing.

Where the gutter line micro-environment is likely to be severe, the underside of metal cladding should be painted using a two pack epoxy primer or elastomeric polyurethane paint before installation.

Building underlay alone can provide this protection if carried down into the gutter, but does not have a 50-year durability if exposed to UV and can give rise to flutter noise if lapped too far into the gutter.

Where roof cladding is exposed to the elements from the underside, it should be included in the maintenance schedule for unwashed areas.

Seagulls perching on ridgings or parapets on buildings can cause damage from rubbish dropped onto the roof, and from their alkali droppings. Discouraging devices such as wire or spikes can be used to prevent this. Unpainted aluminium or AZ coatings are particularly prone to attack from alkali.

16.5 Special Maintenance 

High-risk areas such as around flues, near fumes from exhaust fans, under television aerials or overhanging trees, sites prone to mould, lichen and bird droppings or debris, all need to have extensive manual washing. Proximity to a motorway can cause the collection of fine dust, as can earthworks in the vicinity, and shavings from wood processing plants are often blown into crevices under flashings which retain moisture and can create 'poultice corrosion'.
Bird droppings should be cleared away regularly to avoid premature failure at ridges or bird perches. Canopies above load-out doors have large unwashed areas on their undersides and service station canopies are subject to a harsh environment so they should be treated as a special maintenance cases.


16.6 Inspection 

Building owners should be informed of the maintenance required to keep the cladding within the terms of the warranty, and they should be provided with documentary evidence of their obligations. Regular inspection by specialist consultants should be undertaken annually. Records should be kept of all such inspections, which will support any subsequent claims against the manufacturer, supplier or installer. Records will also assist in the process of mediation or arbitration of any such claims.

Without documentary evidence of regular maintenance, any rectification is solely at the discretion of the supplier. Any subsequent work undertaken on the roof cladding by others that do not comply with this Code of Practice will void any warranty.

Inspections and the reports should cover the fixings, gutters, downpipes, flashings and the surface condition of the cladding. The reports should be placed in the 'Building Maintenance Manual', which should contain dated particulars of the original contract, the type of cladding, it's colour and gauge, the warranty, and reference should be made to any leaks reported and repair work or additions carried out. Regular inspection should be regarded as preventative maintenance.

16.6.1 Installation 

Approved fixers of the members of The New Zealand Metal Roofing Manufacturers Inc (NZMRM Inc) and members of the Roofing Association of New Zealand, (RANZ) will provide a warranty for five years to cover the workmanship and installation of the roof and wall cladding if requested. This means that if the standard of workmanship of the roofing contractor does not comply with this NZ Roofing Code of Practice, and he is a member of RANZ, the installation will be renewed or restored so that it does comply.

This warranty does not extend to any work undertaken on the roof or wall cladding or accessories by other trades or subsequent to completion of the contract by the roofing contractor.

Designers and owners are therefore strongly advised to only deal with members of both of these recognised trade organisations to obtain this warranty.


16.7 Washing 

Regular washing of pre-painted roofing products increases their durability by reducing attack from airborne salts and pollutants. Unpainted products, although not recommended for use in severe or very severe environments, will also benefit from routine washing.

Washing may be carried out with a hose and a soft bristle brush, using fresh water. In areas where heavy industrial deposits dull the surface, a thorough cleaning can be ensured by using a 10% solution of household detergent and fresh water followed by a thorough rinse with clean water.

Stronger concentrations of cleaners than those recommended can damage coating surfaces, and organic solvents and abrasive cleaners should not be used. When cleaning coated surfaces, tar and similar substances may be removed with mineral turpentine, but the surfaces should then be washed thoroughly with detergent and water.

Always clean coated surfaces from top to bottom, and rinse immediately and thoroughly with fresh, clean water avoiding over-cleaning or scrubbing, which can damage painted surfaces.

The scrubbing of bare AZ coated steel cladding can remove the thin factory applied clear acrylic film and should be avoided for this reason.

High-pressure water blasting must not be used to clean pre-painted metal as it can damage the paint surface and water blasting can also force water into areas that it would not be subject to under normal weathering and thus cause water ingress.
If water runoff is used for drinking water, roof outlets must be disconnected before washing any roof or wall cladding using detergents. Care must be taken not to contaminate waterways.

16.7.1 Lichen And Mould 

Some types of local environment are particularly conducive to lichen or mould growth; including areas of wet, dark, or shaded surroundings where trees are in the proximity, overhang roof cladding or low lying valleys where moisture-laden air accumulates as fog or mist.

Lichen is a naturally occurring phenomenon with their spores being dispersed by the wind and lichen will grow even on inert materials such as G.R.P. and glass.

As lichen and mould retain moisture, their removal is in the best interest of the longevity of metal cladding, but recolonisation is very likely. Mould growth can be removed by washing down the roof or wall cladding, and applying a 2% solution of sodium hypochlorite to all surfaces by low-pressure spray, broom or brush.

The surface should be left for 5 minutes but should then be rinsed and thoroughly washed down with cold water. Household bleach contains various concentrations of sodium hypochlorite; therefore, it may be necessary to dilute it.

For example:

  • One brand has 30 g/L solution ( 3% ) — to obtain a 2% solution, 2 parts of bleach should be diluted with 1 part of water. (3 - 2 = 1).
  • Another brand has 40 grams/L solution (4%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 2 parts of water. (4 - 2 = 2).
  • Another brand has 50 grams/L solution (5%) — to obtain a 2% solution, 2 parts of bleach should be diluted with 3 parts of water. (5 - 2 = 3).

If the roof is used for the collection of drinking water see 16.10 Drinking Water.


16.7.2 Graffiti 

Metal wall cladding like most vertical surfaces is subject to being defaced by graffiti. Graffiti removal is likely to affect the pre-painted finishes on metal roof and wall cladding, and before removal is attempted a small area should be cleaned as a trial. Graffiti removers may soften the paint, remove the gloss or may cause permanent damage.

Do not use MEK (methyl ethyl ketone), toluene, acetone or thinners. Overpainting or replacement are the alternative options.

There are clear removable anti-graffiti coatings available but they are an expensive option and should be compatible with the paint system.

16.8 Overpainting 

To achieve a satisfactory result when overpainting it is vital that preliminary preparation is carried out before painting, and the same cleaning process can be used for new, weathered or prepainted roofs.

The surface preparation, painting and over-painting of metal roof and wall cladding should be carried out by specialist contractors.

To achieve satisfactory adhesion and optimum results, all dirt should be washed away and cleaning agents such as soap or detergent should be fully washed off the surface prior to paint application. Over-painting a dirty or wet surface results in poor adhesion of the paint and consequently a reduced life; it can also cause premature corrosion of steel cladding.

Thoroughly clean the surface with fresh flowing water and a medium stiff nylon bristle broom or water blast at 20 MPa ( less than 3 000 p.s.i.). When cleaning the profile of any dirt, lichen or mould, care should be taken not to drive water under laps or flashings.

Rinse the profile swages thoroughly, as any remaining dirt will dry and impair subsequent paint adhesion. Particular attention should be given to the drip edge where the final 15 mm is prone to heavy dirt build-up, and to the coating at the front edge of tile profiles as dirt collects in this area and gives rise to mould and algae growth.

Fallout around flues needs to removed before painting.

Allow the roof to dry.

16.8.1 Unpainted Cladding 

The practice of leaving metallically coated roof cladding to weather before painting is no longer recommended. With the latest developments in primers, roofs can now be painted immediately after installation, and it should be done within one month.

For new AZ coated cladding, only acrylic galvanised iron primers should be used, as solvent-based primers may damage the coating. A solvent-borne corrosion resistant galvanised-iron primer should be used for optimum performance on weathered zinc coated cladding over twelve months old.

After the primer, two coats of acrylic roofing paint should be applied in the selected colour to provide a paint thickness of 50 µm (typically two brush applied coats achieve 50 µm ).

If the cladding is weathered but shows signs of white or red corrosion or damage back to the metal base, proceed with painting as described 16.8.3 Weathered With White Corrosion and 16.8.4 Red Corrosion.


16.8.2 Repainting Painted Claddings 

Repainting painted claddings should be regarded as part of the maintenance programme to extend the life of all metal claddings.
There is an optimum time at which to repaint claddings, and this decision should be made by the owner after specialist consultation.

It is also known as 'the life to first maintenance, ' and is the time before excessive chalking has taken place or the top coat weathered away.

Painted products can be readily over-painted with high-quality acrylic roof paints to extend the life of the roof cladding and if over-painting is carried out while the top coat is still in sound condition there is no need to use a primer.

To prepare the surface for painting all pre-painted products should have their surfaces abraded with a fine grit sandpaper, stiff nylon bristle broom or similar, to improve the adhesion. Care should be exercised not to sand through the existing paint surface on external bends.


16.8.3 Weathered With White Corrosion 

If the white corrosion can be easily removed and no red rusting has developed, the roof cladding should be cleaned as outlined above. Neutralise the areas where white corrosion is present with a proprietary metal cleaner designed for this purpose and follow instructions on the container closely. If all residues from the metal cleaner are not removed before painting, poor paint adhesion will result.

Painting should take place as soon as possible after this pre-treatment. The presence of white corrosion indicates that the primer has been consumed and so isolated areas of white corrosion should be spot primed once these areas have been cleaned and neutralised. If all external bends are showing corrosion, coat the whole area with an acrylic galvanised iron primer.

For unpainted products, it is necessary to use a primer over the whole surface.


16.8.4 Red Corrosion 

Red corrosion, or corrosion at the edges of the profiled steel cladding should be prepared as follows:

Manually de-scale and remove all white and red rust by abrading to bright, firm metal, ensuring that the surface is as smooth as possible. Thoroughly clean the roof as described previously and neutralise the corrosion reaction with a commercially available metal cleaner made for this purpose.

This type of solution should not be allowed to dry on the surface before fully washing off, and all residues of the metal treatment should be removed prior to painting . Dry all surfaces before spot priming the cleaned bare red corrosion affected areas with a zinc-rich primer .

Coat the whole prepared areas with a water based galvanised iron primer and apply two topcoats of acrylic roofing paint to the dry, primed area.

16.8.5 Paint 

High quality, 100% acrylic paint can give a service life of up to 10 years when applied to specification on correctly prepared metal surfaces. This lifespan will vary slightly with colour, roof orientation and the aesthetic requirements of the situation, but poor paint curing will downgrade durability.

Paint should not be applied on wet days, when condensation has not completely dried, on cold days below 10° or hot days above 30°. Windy days are also not suitable, as curing is impaired.

The painting of very hot roofs will result in the evaporation of the solvent before full film formation can take place, and so will reduce the life of the coating.

Ridge ladders should be fitted with protective buffers or rubber pads as they can cause extensive abrasion damage to pre-coated metal cladding. Where it is possible the painter should walk in the pan, but when it is necessary to step on the rib, attention should be paid to sheet overlaps as these may spring up after a painter's weight is removed and reveal an unpainted line.

Decking profiles have a tight roll-formed bend at the top of the upstand and care is necessary to ensure the specified film build is applied in this area.


16.8.6 Brush Application 

The use of nylon brushes is advisable, and these should be wetted with water prior to use to avoid clogging, and in warm weather should be washed out completely at every rest break.

Apply two full even coats of acrylic paint to a dry film build of 50 µm, allowing sufficient drying time between coats, but do not over-brush and thin only sparingly.


16.8.7 Roller Application 

Apply to the spreading rate and film build specified for brush application. Dampen the roller prior to use, then load up the roller and apply two full even coats, allowing sufficient drying time between coats.
Apply with even pressure, and do not over-roll. Profiled rollers are available for corrugated profiles, but some profiles may require the combined use of brush and roller of the paint for complete application.


16.8.8 Spray Application 

Apply to the dry film building specification of a minimum of 50 µm. Airless spray equipment can achieve very high film builds giving rise to runs and uneven coatings. When using spray equipment on hot or windy days, the paint spray may dry before it has reached the metal, which leaves a sandy appearance and feel. This is not aesthetically acceptable and will not provide the even coating required, even though it may measure 50 µm.

Do not spray before 10.00 am or after 3.00 pm as condensation can be present. Outside this time space steel will also cool rapidly, which will impair curing and can result in incorrect film formation. It can lead to early failure of the coating. These hours could be extended in mid-summer to before 9.00 am or after 4.00 pm.

The gloss and weathering characteristics of oven cured and air dried paints are different, and over time a significant difference in colour may become apparent. Variations in natural light conditions will emphasise these differences producing unacceptable aesthetic variations. For this reason, the whole roof area should be painted and not patch painted and this also is the reason why 'touch-up' paint should not be used.

Spray cans should not be used for repairing scratches on pre-painted cladding. Minor surface scratches are best left because they become less noticeable as the coating weathers. If the scratch cannot be seen from the ground, it should be left alone.


16.9 Material Selection 

The selection of the most suitable material for metal roof and wall cladding, compliant with the durability requirements of the NZBC, depends on the design of the building and its location or environmental category.
Manufacturers offer different metallic and paint coatings and different metals that are suitable for all different environments.

Designers are urged to select the material in conjunction with the conditions of any expected warranty before the material is specified. The durability of the material is not necessarily confined to the number of years stated in a warranty and is only indicative of the performance of different substrates and coatings.

Those factors that the designer can influence are covered in many other sections of this Code. Cost and colour should not be the major determining factors, and designs using unwashed areas or detailing using different metals requires careful material selection.

Any warranty for roof or wall cladding is divided into two parts, the material, and the workmanship. Workmanship warranties are usually provided by the Roofing Contractor for a minimum period of two years; however, this period is extended to five years by Roofing Contractors who are members of RANZ.

There is a difference between the warranty offered for residential and commercial use of metal roof and wall cladding.

The maintenance of metal roof and wall cladding is very dependent on two factors - design and materials.

The preparation of a maintenance manual for owners is an indication to the owner that periodic maintenance is required to comply with the manufacturer's warranty conditions.


16.9.1 Residential 

Consumer expectations include appearance in relation to performance, but the NZBC does not. The ease of replacement might satisfy the Building Code, but not always the consumer.

Trade literature is available from the coated steel or pre-painted metal supplier and the product manufacturer which sets out prescriptive design, installation and maintenance instructions that should be adhered to if a warranty is to be upheld.

Although the product manufacturer or the contractor has no control over the maintenance part of these conditions, they are obligated to inform the owners or their representatives of the maintenance requirements specific to the material to comply with the NZBC.

This material warranty is for a minimum of 15 years against perforation unless specifically stated.


16.9.2 Commercial 

Material selection for commercial and industrial construction may require a different approach if the maintenance can be carried out as tax-deductible expenditure.

Any commercial warranty offered by the coated metal or prepainted metal supplier is specific for the environment and end use, and a request should be made to the supplier before installation as they are only issued upon the satisfactory completion of the contract.

Such warranties are also issued for different types of metal substrate and coatings only on condition that the requirements for their use and maintenance are complied with.


16.9.3 Responsibility and Liability 

There is a joint responsibility between all the parties to ensure compliance with the terms of the warranty.

The designer, manufacturer, contractor, roofing contractor, and the owner should be made aware of their responsibilities, and all parties are considered to have been informed of their obligation if they have sighted or signed a warranty.

If the requirements of the NZBC or consumer legislation knowingly cannot be met, or if the conditions of the warranty or the requirements are knowingly impractical or ignored, the liability remains with those who ignored them. There is an implied warranty requirement within the Building Act that the material selected and used will be suitable for purpose. The material can be used without compliance with the NZBC, but only on a written statement to that effect given by the roofing contractor and with the consent of the T.A.

16.9.3A Metallically Coated Cladding Endurance and 16.9.3B Naturally Washed Cladding Endurance give an indication of the period that metal roof and wall cladding will not perforate from corrosion in a well-washed situation providing maintenance requirements are met. See 16 Maintenance

In unwashed areas the durability of wall cladding, spouting or flashings are likely to be less than that indicated in the tables.

16.9.3A Metallically Coated Cladding Endurance and 16.9.3B Naturally Washed Cladding Endurance do not necessarily consider the aesthetic appearance of the metal coating or the 'life to first maintenance '. See 16.8.2 Repainting Painted Claddings.

The indication for rainwater goods depends on the environment and the ability of any spouting or gutter to be able to drain and avoid ponding.

The COP strongly recommends an enquiry into the terms and conditions of an expected warranty before finalising material selection and issuing tender documents, as 16.9.3A Metallically Coated Cladding Endurance and 16.9.3B Naturally Washed Cladding Endurance are not warranties.

The range in years provides for differences in each environmental category as described in 4.6 Environmental Categories.

COP Category B — Moderate Inland.
COP Category C — Moderate Marine
COP Category D —Severe Marine
COP Category E — Very Severe Marine


Important: Check with supplier as materials used in these areas may not satisfy the durability
requirements of the NZBC.

R/W = Roof and walls

RGS = Rain-water Goods



16.9.3A Metallically Coated Cladding Endurance


Environmental CategoryB/C D E B/C DE
Galvanised Z450
AZ 150
Prepainted AZ150
Prepainted AZ200






16.9.3B Naturally Washed Cladding Endurance


Environmental CategoryB/C D E B/C D E B/C D E
Unpainted aluminium
Polyester/Acrylic Aluminium
PVF2 Aluminium
Stainless steel


16.9.4 Special Environments And Exclusions 


  • Maintenance requirements not fulfilled.
  • Unwashed areas.
  • Garage Doors.
  • Damage due to handling, storage, roll-forming and installation.
  • Design not in accordance with N.Z. Roofing Code of Practice.
  • Consequential loss.
  • Accumulation of debris.
  • Geothermal areas.
  • Internal environments from fumes or pollutants.
  • West Coast South Island.


16.10 Drinking Water 

Rainwater collected from roofs clad with steel and prepainted steel products will comply with the provisions of NZBC G 1 2.3.1, provided the water is not contaminated from other sources.

The first 25 mm of rainfall from a newly installed roof should be discarded before drinking water collection starts, and always disconnect downpipes when painting a roof. Spouting should be regularly cleaned to avoid the build-up of dirt and debris that can affect water quality.

Where a paint or paint system is applied to the roof, its suitability for the collection of drinking water should be established. When rainwater from pre-painted roof cladding is used for drinking, it is advisable to repaint the roof as soon as its surface has weathered.

Water collected from metal roof cladding, spouting or gutters made from aluminium, copper and stainless steel will not normally be contaminated by rainfall in suburban and rural areas. However, fallout from manufacturing plants, top dressing, and the contamination resulting from roof cleaning can affect the water quality, and in these cases downpipes should be disconnected.


16.11 Storage 

Roof and wall cladding must be kept dry, covered and protected from damage while stored on the site.

When sheets are to be stored on the ground, they must be stacked horizontally on a firm and level surface on top of cross-stacked untreated timber fillets, inclined slightly for rainwater runoff and be covered with a loose tarpaulin allowing air to circulate.

Sheets should be stacked in sheltered positions preferably near areas of the building where it is to be fixed, and they should be stacked in the order in which they will be used.

The height of such stacks should not exceed 1 m, and they should be clear of the ground. If it is necessary to stack sheets in an exposed position, they should be secured against any movement by the wind.

Well ventilated storage is essential as rainwater, or condensation in humid weather can penetrate and damage close-stacked metal cladding by capillary action. Always store metal products under cover in clean, well ventilated buildings.

Once packs are opened and laying of the roof or wall cladding commences, a continual visual check should be made to ensure the surface of the sheets are free of any noticeable defect or damage. This is particularly important with pre-coated materials.