COP v3.0:maintenance; material-selection

15.9 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.

 

15.9.1 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, it is his obligation to inform the owner or his representative 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.

 

15.9.2 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.

 

15.9.3 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.

15.9.3A Metallically Coated Cladding Endurance and 15.9.3B 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 15 Maintenance


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

15.9.3A Metallically Coated Cladding Endurance and 15.9.3B Naturally Washed Cladding Endurance do not necessarily consider the aesthetic appearance of the metal coating or the 'life to first maintenance '. See 15.8.2 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 15.9.3A Metallically Coated Cladding Endurance and 15.9.3B 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

 

 

15.9.3A Metallically Coated Cladding Endurance

INDICATIVE PERFORMANCE IN YEARS THAT NATURALLY WASHED METALLIC COATED STEEL BASED CLADDING WILL NOT PERFORATE FROM CORROSION.

Environmental CategoryB/C D E B/C DE
CoatingR/WR/WR/WRGSRGSRGS
Galvanised Z450
AZ 150
Prepainted AZ150
Prepainted AZ200
15/30
15/40
30/40
30/50


15/25
20/40



15

10
10/15
12/15


10
10



 

15.9.3B Naturally Washed Cladding Endurance

INDICATIVE PERFORMANCE IN YEARS THAT NATURALLY WASHED METAL CLADDING WILL NOT PERFORATE FROM CORROSION.

Environmental CategoryB/C D E B/C D E B/C D E
CoatingRoofRoofRoofWallWallWallRGSRGSRGS
Unpainted aluminium
Polyester/Acrylic Aluminium
PVF2 Aluminium
Zinc
Copper
Stainless steel
25/40
30/50
35/50
>50
>50
>50
20/30
25/50
30/50
>50
>50
>50
15/25
20/40
25/40
50
>50
>50
15/40
25/45
30/45
>50
>50
>50
15/30
20/40
25/40
>50
>50
>50
10/20
15/35
20/35
50
>50
>50
10
15
15
10
>50
>50
10
15
15
10
>50
>50
5
10
10
10
>50
>50

 

15.9.4 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.