New standard puts builders in the frame

Ten years after the present building standard for timber housing was written, a new guide has been devised, writes Ric Oram.

Standards New Zealand has produced a new guide to building timber-framed houses, NZS3604:1999. "It will make it easier to gain building consents," promises Neil Gerrish, building control manager at Porirua City Council and chairman of the committee which has produced the new standard.

It is also a guide to complying with the building code but is not mandatory, so designers, architects and builders do not have to follow it.

However, when the Building Industry Authority approves it, probably next year, local bodies will not be able to refuse building consent applications that comply.

About 90 per cent of new houses in New Zealand are built of timber. This standard applies to most of them up to three storeys high, to garages and also some light commercial buildings.

The existing standard for timber-framed buildings is 10 years old. Structural requirements in the new one are not changed, but some restrictions on lintel spans are eased.

The building code, introduced in 1992, outdated some of the old standard - for example, the code's requirement that structural fittings have at least 50-year durability - so a section on durability is introduced.

"In New Zealand, exposure to sea-laden winds is high," says Claire Benge, an architect and technical adviser to the authority, who helped draw up that section. "As our cities grow, buildings are on more exposed sites with more complex foundations."

The standard therefore covers what coatings are advisable for harsher coastal or thermal atmospheres compared with, say, relatively dry Central Otago. It requires stainless steel for sub-floor metal fixings in sea spray zones, for example.

The committee thought about requiring stainless steel within 5km of the sea, but Gerrish says modern powder coatings and paint applications made this unnecessary.

The standard also contains explicit information on laying foundations which, under the code, must not show signs of destabilising for 50 years.

Loading requirements are based on up-to-date information - gone is a requirement for all houses to be able to take the weight of snow, even in areas like Auckland where that would never happen. A table indicates snow loadings required for a range of areas and conditions.

Standards New Zealand is taking orders for the new standard (04 4985991; fax, 04 4985994; e-mail, www.standards.co.nz). It is in hard copy (retailing for $232, plus GST. The 400 pages are in a loose-leaf ring binder in easy-to-read English with commentary and explanatory notes in margins. Also contained is most of the MP3600 builders' guide.

It is the first standard produced on interactive CD-Rom, with the pages presented in portable digital format, and drawings and diagrams on CAD files which can be downloaded and modified. The CD-Rom ($295, plus GST) is also available with a Web browser on the disk ($395, plus GST).

This is also the first standard to carry advertising by building industry players.

The Building Industry Authority, Building Research Association, Registered Master Builders and Standards New Zealand will conduct a series of seminars on the new standard - in Auckland on June 23 and August 10 and in Taupo, Hamilton, Rotorua and Tauranga from July 5 to 8.