New Zealand Building Code clauses E3 – Internal Moisture and G4 – Ventilation focus on air quality and accumulation of moisture in occupied spaces. The acceptable solutions for these clauses do not specifically require 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 requires 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 ceilings which allow easy passage of moisture vapour.
Long (over 12 m spans), shallow pitched (less than 12°) roofs should also be designed to allow natural ventilation.
Generally, there is no need to make provision for moisture control in industrial and most commercial buildings due to them being either well ventilated or climate controlled. In buildings with valuable or delicate stock, the possibility of dripping condensation needs to be assessed.
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, require specific design.
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.