Simplification of timber treatment DBH Building Controls Update No 113

Issue 26 – April 2011

New timber treatment system

A simpler system for timber treatment will come into effect from 4 April 2011, through the Department of Building and Housing's amendment of the Acceptable Solution B2/AS1. The new timber treatment system retains and, in some aspects, improves the current level of consumer protection and may also reduce costs.

The changes follow public consultation by the Department of Building and Housing (the Department) in September and October 2010. Submissions were overall strongly supportive of the proposals, which are adopted with little change but some clarification. A summary of key issues raised in the consultation is available on the Departments' website (

One treatment class for enclosed framing

The changes allow a single treatment class, H1.2, to be used for nearly all enclosed framing. The current system has as many as four different classes of timber, including untreated timber, used to frame a house. This is complex and can lead to mistakes on site.

Streamlining the use of treated timber is expected to reduce errors in the use of timber, and to simplify choice and supply inventories. It should also make the consent and inspection process more straightforward.

The H1.2 treatment class has a boron treatment. Recent scientific research has shown that, for framing timber, H1.2 boron provides comparable protection against fungal decay to LOSP H3.1. In some parts of buildings, such as internal walls, the level of protection will increase.

The changes apply only to Radiata pine and Douglas fir; not to other species.


There are two exceptions to the single treatment class:

  • cantilevered deck joists and framing require a higher treatment class, H3.2, as cantilevered decks depend more critically on the strength of the timber to prevent collapse
  • untreated Douglas fir can be used for houses of a defined low-risk design. Douglas fir is more resistant to decay than untreated Radiata pine, but not as resistant as treated Radiata pine.

Transition period

A transition period of about 3 months will give industry time to adjust to the changes, which come into effect on 4 April 2011. From that date until 30 June 2011, both the current and the new versions will apply as Acceptable Solutions for consenting purposes. From 1 July 2011 only the new B2/AS1 will apply as an Acceptable Solution.

The new system is being publicised in March, April, and May through a nationwide series of BRANZ seminars. Building consent officials, architects and designers, and builders who wish to attend should register now at

The proposed changes are part of the Government's drive to make it easier for everyone to access, understand, and comply with the Building Code and hence to 'build it right first time'.

For online services and previous versions of Building Controls Update, visit the Department's website To ask a question or get more information, call the Department on 0800 242 243 or email

Information supplied by the Department of Building and Housing.

Related Standards

Published in building.