The project to review the foremost building Standard in New Zealand for the building and construction industry, Timber-framed buildings NZS 3604:1999, is now well underway. The draft revised Standard is planned for public comment release in late 2009. Publication is scheduled for late 2010/early 2011.

In the May and June issues of Touchstone and Standards magazine, we profiled the leadership group http://www.standards.co.nz/touchstone/Issue+05/Building/default.htm#1 and technical committeehttp://www.standards.co.nz/touchstone/Issue+06/Building/default.htm#1. Below, we profile the work groups for 3604.

Introducing the five work groups

There are five industry specific work groups currently working on specific assignments. These groups are made up of members of the technical committee, organised by their particular area of interest and expertise, working under the guidance and direction of the technical committee. Primarily they are responsible for identifying issues within their specific areas that need updating in NZS 3604, and for recommending changes to the technical committee for a final decision (see Figure 1 for further information on the work group process).

Loadings work group

This group is responsible for recommending changes to NZS 3604 to reflect AS/NZS 1170, the loadings Standard. AS/NZS 1170 is referenced in the Compliance Documents to the New Zealand Building Code effective 1 December 2008. Some of the recommendations made by the loadings work group are to:

• make changes to seismic maps to provide better clarity
• change the soil types in earthquake clauses to align with AS/NZS 1170
• add an extra high wind zone
• add gradients – currently there are three gradients in NZS 3604: gentle, moderate, and steep. Three additional gradients have been recommended – low, mild, and very steep.

Bracing work group

Recent research undertaken by BRANZ has identified areas in NZS 3604 section 5 – Bracing, that need updating. While the content is still accurate, a number of problems have been identified with readability and a perception that some content is too open to interpretation, which can cause problems for territorial authorities. Some of the recommendations made by the bracing work group are:

• amalgamate test method BRANZ P21 and technical recommendation TR10 into a single updated wall bracing test method
• limit bracing unit ratings on timber floors to 120 BU/m
• limit BU ratings on concrete floors to 150 BU/m
• strengthen the bracing distribution rules – it has been agreed that the current distribution rules (internal lines 70 BU, external lines 10 x L BU) are inadequate. The group recommends that minimum requirements be increased to 15 x L BU for external walls with no wall less than 100 BU (including internal walls). In addition, the group recommends a demand-linked minimum, equivalent to D (demand) dividing by 2 n where n is the number of bracing lines in the direction being considered. Diaphragms have been recommended to be supported by elements rated no less than 100 BU or 15 x L BU, whichever is greater.

Durability work group

The durability section needs to be updated to align with the recent changes to the New Zealand Building Code and other Standards: in particular, the maps and recent product developments content need to be reviewed. Some of the recommendations made by the durability work group are to:

• remove all building envelope and weather-tightness areas including flashings and so on as they are to be covered in the Compliance Document E2/AS1. Section 4 – Durability is to cover structural details only
• keep and update corrosion map figure 4.1 to include major cities and towns to make it more reader friendly. Add a note stating the map is indicative only and must be read in conjunction with AS/NZS 2312 clauses for atmospheric corrosivity categories B, C, and D
• change zones 2 and 3 to Zone B
• change zone 1 to Zone C
• change seaspray zone to Zone D.

Roof framing work group

Building practices have moved ahead significantly in the past 10 years and NZS 3604 needs to be updated to reflect current technical knowledge and industry practices – section 10, Roof framing is an example of this. Roof trusses are no longer designed by the designer; they are currently designed and manufactured by producers and fall outside the scope of NZS 3604. Although roof truss design falls outside the scope of NZS 3604, it is recognised as a major component of timber home design and construction today. The roof framing work group believe this should be acknowledged in the revised Standard.

Some of the changes recommended by the roof framing work group are to:

• remove roof space bracing for all hip and light gable roofs because it is difficult to achieve space bracing in line with NZS 3604
• add a clear definition of hips and gables to NZS 3604
• revise truss to top plate fixing to one type, for example, two skewed nails and two wire dogs as standard
• acknowledge trusses as a proprietary system and that providing it complies with NZS 3604, and all supporting documentation including design statements is provided, it should be acceptable
• acknowledge proprietary garage beam lintels and other proprietary lintel products in NZS 3604. It was recommended that these could be covered in the foreword.

Design clarity work group

Primarily responsible for reviewing the figures in NZS 3604 for appearance and clarity, this group is in the early stages of reviewing the figures and has not yet made any recommendations for change to the technical committee.

Representatives on the work groups

Work group	Representatives
Loadings	Antony Cook, Ian Garrett, Ernest Lapish, Graeme Lawrance, Roger Shelton
Bracing	Mark John Ash, Warwick Banks, Douglas Gaunt, Hans Gerlich, Roger Shelton
Durability	Eddie Bruce, Tony Castledine, Stuart Hayman, Graeme Lawrance, Michael Middlebrook, Stephen Walker
Roof framing	Mark John Ash, Antony Cook, Stuart Hayman (Observer), Richard Merrifield, Jamie O'Leary, Stephen Walker
Design clarity	Eddie Bruce, Colin Clench, Colin Hill, Michael Middlebrook, Jamie O'Leary, Allan Walters

The technical committee is responsible for considering all recommendations for changes to NZS 3604 proposed by the work groups. Through consensus-based discussion, this committee makes the final decisions on what changes will be made to NZS 3604 prior to final preparation. Once the draft is completed, it will be released for public comment.

Work group meetings are conducted independently of technical committee meetings. During these meetings, recommendations for changes to NZS 3604 are tabled and debated by the work group to reach a consensus. When consensus is reached, a change recommendation is scheduled to be tabled at the next technical committee meeting. If consensus is not reached on a particular issue at work group level, the issue is debated further until a consensus is either reached or the matter is recorded and dropped.

If the technical committee is unable to reach consensus on a recommendation that has been tabled by a work group, the matter is referred back to the recommending work group for further discussion and debate (see Figure 1 for further information).

Note: The recommendations discussed in this article are by no means a full representation of the issues discussed to date by the technical committee or the work groups formed to undertake the project to review NZS 3604:1999 Timber-framed buildings. Nor are they a final representation of decisions made to date. They are provided as background information to introduce readers to the work groups.

For more information, please email mani.taare@standards.co.nz, or call 04 495 0934.