Leaky Buildings: New Requirements/Good Practice
The Building Industry Authority (BIA) has released new requirements that define good practice for the way buildings are designed and built. These changes are aimed largely at helping overcome leaky building problems. The new requirements, or "Weather-tightness Solution", contain much more detail and guidance (than in previous requirements) for architects, builders and building inspectors on how buildings should be designed and built to prevent leaks or to manage them if they occur.
An underlying "philosophy" of the changes are the "4Ds" principles of water management in buildings. They are, in order:
- Deflection - that is keeping rain away from sensitive areas by using features like eaves or flashings;
- Drainage - providing "paths" for water that gets behind cladding to drain away (drained cavities are an example of this);
- Drying - removing water that leaks through a cladding and does not drain away - principally through ventilation; and
- Durability - making sure materials used to construct walls and roofs have an appropriate level of durability for the situation they will be used in.
Some Practical Details
The changes will apply to timber framed buildings up to three storeys or 10 metres high (this includes most standard houses and low-rise apartment buildings). The main elements of the changes are:
- introducing a "risk management approach" to weather-tightness protection (in practical terms, this means the more at risk a building is of leaking - based on a range of factors like complexity of design and exposure to wind - the greater the protection required to stop water getting in);
- much more detail around the design of water protection features like flashings and cappings for parapets;
- including more cladding types than under the old requirements;
- the need for drained cavities in a wider range of building situations; and
- more detail around designing "problematic" areas like decks, balustrades and balconies.
These changes will apply to projects where consents are applied for from 1 February 2005. People who have received consents before 1 February 2005, under the existing "Acceptable Solution", have until 31 January 2006 to finish their building work and obtain a code compliance certificate.
The Cost of the Changes
The cost of the changes vary according to the type of building. For example, additional costs for a simple brick house would be minimal - around $500. However, for a non-brick house requiring a drained cavity and the new flashing details, the cost could be $5,000 or greater, depending on house size. The average cost increase over all new houses is estimated to be $2,500. The additional cost for apartments will also vary, but the average cost increase over all new apartments is estimated to be $3,000.
Contact for Enquiries
The Ministry of Agriculture and Forestry
Pastoral House
25 The Terrace
PO Box 2526, Wellington
Tel: 0800 00 83 33
Fax: +64 4 894 0720
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