Bia Proposes Changes To Treated Timber And External Moisture Management

The Building Industry Authority has announced proposals for significant changes to its Approved Documents that set out how timber should be treated and the way external moisture should be managed in residential dwellings.

“Our overriding goal in proposing these changes is to put in place a robust regime that provides a sufficient level of protection for consumers,” BIA chief executive Richard Martin said.

“Timber treatment and external moisture management have been identified as important issues in the weathertightness problem – these proposals are important steps in the wider body of work being undertaken by the BIA, other parts of Government and the industry to help resolve that problem.”

Approved Documents provide a prescriptive but non-mandatory means of complying with the New Zealand Building Code. Buildings built to the method described in an Approved Document are automatically deemed to comply with the Code. Buildings can be built using design or construction methods that differ from an Approved Document but these must be considered on their individual merits by a territorial authority or building certifier using the approved documents as a benchmark.

Treated Timber The current regime allows the use of untreated kiln-dried timber in the framing of buildings. The changes proposed will require all timber framing to be treated to a minimum level of H1.2 to protect against insect and fungal attack.

This will take us back to a pre-1990s like regime for treated timber when there was a greater level of safety, or margin for error, built into the system.

Proposed changes to the use of treated timber include: A requirement that all framing timber in residential constructions must be treated to a minimum level H1.2, sometimes known as H1 Plus. This includes framing for external walls, internal walls; sub-floor framing; roof frames and trusses and ceiling and inter-storey joists. The minimum level of treatment required for parapets and balconies exposed to the weather or covered by cladding, and for all cantilevered parapets, balconies or decks will be H3. Increased identification requirements for treated timber to avoid confusion and mix ups on building sites and ensure correctly treated timber is used in the right situation.

The proposed changes are consistent with the already announced proposed changes to the New Zealand Standard for treated timber.

External Moisture The proposed changes to the Approved Documents for external moisture management provide more extensive prescriptions for complying with the external moisture requirements of the Building Code. Changes include Providing more detail in prescribing how certain building materials (including some so-called “monolithic claddings”) should be used to help prevent buildings from leaking. Broadening the range of claddings covered by the Approved Documents. Providing more direction regarding the design and use of flashings. Introducing a requirement that cavities be built behind claddings in situations that are considered to be a high risk for leakage (cavities provide an opportunity for moisture to drain or evaporate before causing damage to building materials).

Mr Martin noted that the external moisture management and treated timber proposals were very closely linked.

“The moisture management proposals are in large part about keeping the rain out. But they also acknowledge that at some stage during the life of a building it could leak. Elements such as the cavity proposals and the treated timber proposals are about helping a building to manage or cope in the event of a leak.”

He stressed the importance of seeing the treated timber proposals as mitigation measures in the event of buildings leaking, not as a total answer or as a preventative to the so-called leaky building syndrome.

“Treated timber may still rot following prolonged exposure to moisture, even at the treatment levels being proposed.

“However, the spread and rate of decay and fungal growth will be slower than with the untreated framing timber currently used. This improves the prospect of leak-related problems being identified and remedied before major structural damage occurs.

“So, what we are doing is working on the assumption that all buildings have the potential to leak and these measures are designed to help the building cope with that eventuality and to allow owners or occupiers more time to spot problems before major structural problems occur.”

Consultation Process Mr Martin said the BIA has now begun an eight-week consultation process on the proposed changes.

“That consultation process is very important. The proposed changes are significant and we are encouraging all parts of the industry and other interested people including consumers or consumer groups to participate.”

Once the consultation period closes the BIA will review and consider all comments received and the Authority will then make its final decisions.

The closing date for submissions on the proposals is 8 August 2003.

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