*ARCHIVE* - Weathertightness Solution - a significant advancement in combating leaky building problems 23 June 2004
Information and advice
Weathertightness and Acceptable Solution E2/AS1.
Media release 23 June 2004
The BIA has released new requirements that define good practice for the way buildings are designed and built to help overcome leaky building problems.
"The changes are aimed at achieving better buildings for New Zealanders," chairman Barry Brown said.
"They're aimed at providing better protection against leaks for building owners and users and they represent the best New Zealand and international thinking in building science.
"Together with the recent changes to treated timber requirements, we have now addressed many of the underlying technical causes of leaky buildings problems. The Building Bill now before Parliament will also provide a range of measures to improve building performance for owners and users."
The new requirements, or Weathertightness Solution, contain much more detail and guidance for architects, builders and building inspectors on how buildings should be designed and built to prevent leaks or to manage them if they occur.
Important Elements of the New Requirements
The BIA is changing its Acceptable Solution (technically called E2/AS1 but sometimes referred to as the 'Weathertightness Solution') for the way buildings manage external moisture (weathertightness).
An underlying philosophy of the changes is the adoption of the '4Ds' principles of water management in buildings.
The 4Ds (in order of importance) are:
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.
Durability - making sure materials used to construct walls and roofs have an appropriate level of durability for the situation they will be used in.
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). Key elements of the change are:
- The introduction of a risk management approach to weathertightness protection. That is, 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.
- The inclusion of more cladding types than under the old requirements.
- The need for drained cavities in a wider range of building situations.
- More detail around designing problematic areas like decks, balustrades and balconies.
The BIA has also introduced a testing method to allow cladding manufacturers to prove the weathertightness performance of their products when used as part of an overall cladding system that includes a cavity.
Timing of Changes
The BIA has announced a staged implementation of the changes:
- The changes will apply to projects where consents are applied for from 1 February 2005 - this gives time for councils and the industry to have any operational changes needed in place.
- People who have received consents prior to 1 February 2005 under the existing Acceptable Solution have until 31 January 2006 to finish their building work and obtain a code compliance certificate.
These dates are subject to final feedback from the sector to ensure there are no significant unforeseen operational issues that would make the 1 February 2005 implementation impractical.
Impact of Changes
The New Zealand Institute of Economic Research undertook a cost/benefit study of the changes for the BIA.
This showed the impact would vary according to the type of building involved. They estimated 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 size. The average cost increase over all new houses is around $2,500.
The additional cost for apartments will also vary, but the average cost increase over all new apartments was estimated to be $3,000.
Mr Brown said the Authority had considered these implications very carefully when deciding on the changes and that they have been subject to rigorous consultation and peer review.
"Ultimately though, they are a relatively small cost when considered over the life of a building and against the tens of thousands of dollars required for fixing leaky building problems - not to mention the emotional cost involved."
The study showed a net benefit of $800 million would result from the changes over the next 25 years, largely as a result of not having to repair leaky buildings.
Mr Brown also said people involved in the building industry - manufacturers, architects, builders, and building inspectors - would need to do things differently as a result of the changes and this would lead to better building outcomes.
"Many in the industry will welcome these changes, and we have had significant industry input into determining them.
"Our key message to the industry is that these changes are aimed at achieving better buildings for New Zealanders - and that is in the interests of everybody.
"We also want to assure the industry we are fully committed to working with them to implement these changes."
Contact: John Walsh - 027 258 2849
Explanation of Acceptable Solutions
The BIA is changing the Acceptable Solution for Clause E2 of the Building Code (technically known as E2/AS1). This clause covers the way buildings should be built to provide adequate resistance to the penetration and accumulation of moisture from the outside.
Acceptable Solutions provide a prescriptive means of complying with the Building Code. They set out a building method, which, if followed, means a building is automatically deemed to comply with the relevant part of the Building Code.
Acceptable Solutions are not mandatory.
A building can be designed and constructed in a way that differs partially or totally from an Acceptable Solution but can still comply with the Building Code. This is known as an Alternative Solution and must be considered on its merits on a case-by-case basis by a council or building certifier when determining code compliance.