COP v3.0:durability; crevice-corrosion

1 Introduction 

The NZ Metal Roof and Wall Cladding Code of Practice (COP) is published by NZ Metal Roofing Manufacturers Inc. (MRM), to provide:

  • acceptable trade practice for the fixing of metal roof and wall cladding and accessories.
  • prescriptive detailing for designers and sets a benchmark for the standard of detailing and workmanship required over and above that required to comply with the NZBC.

The COP does not describe or dismiss alternative methods, which may need specific acceptance by the Building Consent Authorities.

It is published in accordance with current technology, materials, and building codes. The COP will be periodically updated to reflect changes in legislation and standards, or improvements in technology and available materials.

The most current Code of Practice is available on the MRM website, www.metalroofing.org.nz/cop, as Code of Practice Online (MRM COP Version 3).

Print options and downloadable illustrations are available from the MRM website, however, copyright remains with NZ Metal Roofing Manufacturers Inc.

2 Glossary 

The glossary section provides definitions and descriptions of commonly used terms, as well as illustrations of domestic cladding terminology, industrial cladding terminology, and profile geometry.

 

 

3 Structure 

Load Design discusses design and installation elements to ensure roofs are structurally sound and meet the objectives for the NZBC B1 Structure.

Topics include:

  • AZ/NZS 1170:2011
  • NZS 3604
  • Understanding loads
  • Fastener performance
  • Profile shape
  • Wind load span graphs and fixing patterns.

4 Durability 

Corrosion (B2-Durability) covers considerations for continued performance of roof and wall cladding over the building lifecycle.
Key topics include:

  • Material performance and coatings.
  • Corrosion: evironmetal categories and special climates.
  • Material compatibility — both "in contact with" and "runoff onto".
  • Maintenance for prevention and remediation of corrosion.

5 Roof Drainage  

The Roof Drainage section coincides with the NZBC Clause E1 Surface Water. It describes how to drain rainwater from roofs quickly and effectively. Topics include:

  • Rainfall Intensity
  • Roof Pitch for Drainage
  • Gutter and Downpipe Design
  • Gutter and Downpipe capacity calculations.

6 External Moisture 

The design and installation of metal roofing is greatly influenced by the laws of physics, which include the conductionand radiation of heat and the convection of air. Both designers and Roofing Contractors should be aware of thisinfluence. This section in the COP deals with:

  • Heat.
  • Thermal Movement.
  • Weather Thightness.
  • Profile Strength.

7 Flashings 

This section contains acceptable and better flashing details for most possible junctions, but does not require the use of welting, seaming or crimping, which are used with flashing standing seam cladding. These techniques are described in Standing Seam Cladding, but they can be used to substitute any sealed lap in lieu of mechanical fastenings. 

Flashings in this Code does not contain specific details of the interface with alternative roof cladding materials, such as butyl rubber, but the same good practice is applicable.

 

8 Penetrations 

In this COP a penetration is any hole cut in roof or wall cladding to accommodate projections such as pipes, ducts, chimneys, doors and windows. The type of penetration design is determined by how large the hole is, what shape it is, the pitch and type of the roof, the catchment area, placement on the roof, and how it matches the module of the cladding.

9 Roof Ventilation  

The science of internal moisture control is concerned with the need to manage and control condensation.  
The condition of the outside environment, the building design, and occupant behaviour affect humidity in the living spaces, which ultimately affects humidity in the ceiling space.  
This section of the COP focusses predominantly on managing humidity in the ceiling space of dwellings.
Shorter sections also cover the design of wall cladding. Non-residential roof and wall cladding may be affected by the need to control internal moisture.

 

10 Natural Light 

Clear Roof Sheeting explores the materials and installationg methods availve to provide natural lighting solutions for buildings in NZ. Other topics include:

  • Types of roof light.
  • Weathering and Durability.
  • Loadings for roof lights.
  • Termal movement

11 Fitness For Purpose 

In addtion to Corrosion (NZBC: B2 – Durability), other issues which may affect the lifespan or perceived quality of metal roof and wall cladding, include:

  • Oil Canning.
  • Purlin Creasing.
  • Colour Differential.

12 Site Practice 

Guidelines for site practice, including:

  • Safety.
  • Transportation and Handling of Material.
  • Walking on Roofs.
  • Tools of the Trade.

13 Installation 

Metal roof and wall cladding should be installed as explained in this section to comply with the NZBC and to satisfy manufacturers' warranties.

To minimize the risk of wind damage to partially clad structures during construction, it is necessary to plan the sequence and method of cladding.

14 Other Products 

Other roofing products, include:

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

 

15 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 Testing 

Section 15 sets out the design and performance requirements for sheet roof and wall cladding systems specifically for New Zealand. While it is intended that only those people associated with testing would be concerned with the details of the test procedures it is of general and historical interest as to the reasoning behind the performance requirements.

For this reason a commentary is provided which follows each part.

Section 15 is divided into general requirements and specific methods of testing sheet roof and wall cladding for point load and also to determine their resistance to wind pressures. (UDL - uniformly distributed load).

These procedures apply to all metals and plastic sheeting however because of their different characteristics some of the performance criteria are different.

17 Useful Information 

Useful tools and tables to do calculations and conversions for roof and wall cladding. Just choose the correct online caculator, input your values, and get the answer.