The NZ Metal Roof and Wall Cladding Code of Practice is a comprehensive design & installation guide, and a recognised related document for Acceptable Solution E2/AS1 of the NZ Building Code.
New Zealand Building Code clause E3 – Internal Moisture, and G4 – Ventilation, both focus on air quality in occupied spaces. The NZBC does not specifically require the ventilation of attic spaces.
While problems with excessive internal moisture in attic spaces are relatively uncommon, they can be severe. A poorly designed ceiling cavity, even above a well-aired room, can give rise to internal moisture problems in the attic space, which can affect the air quality of the occupied space below and may cause health and durability issues.
The COP recommends using building techniques which encourage trickle ventilation of all spaces in buildings and requires specific ventilation design for flat roofs, sarked roofs, skillion roofs, and roofs with open ceilings.
Roofs in cold areas where numbers of people may come in wet at the end of the day, such as ski lodges and tramping huts, also require specific design.
Generally, there is no need to make provision for moisture control in industrial and most commercial buildings. Buildings designed to accommodate large numbers of people such as theatres, sports areas and educational buildings, and areas creating particularly high moisture levels—e.g., swimming pools—should have ventilation solutions designed by a specialist engineer.
Safeguard people against illness, injury, or loss of amenity that could result from the accumulation of internal moisture.
Buildings must be constructed in a way that avoids damage to building elements due to the presence of moisture.
NZBC Clause E3 requires building practices to ensure an adequate combination of thermal resistance, ventilation, and space temperature in all habitable spaces, bathrooms, laundries and other spaces where moisture may be generated or accumulate.