Revision of Standard for timber-framed buildings

Standards New Zealand Media Release

17 June 2009

Revision of Standard for timber-framed buildings NZS 3604 – update

A ‘limited technical review’ of NZS 3604:1999, the key Standard for building timber-framed houses in New Zealand, is now underway. The Department of Building and Housing and the Earthquake Commission have sponsored the revision and the draft revised Standard is planned for public comment release in late 2009. Publication is scheduled by late 2010/early 2011.

NZS 3604 sets a minimum standard for the design and construction of timber-framed houses in New Zealand. About 90% of timber-framed houses in New Zealand feature elements of NZS 3604 in their design and construction, and timber-framed houses designed to NZS 3604 give consumers assurance that their house will meet legislative requirements.

Architects, designers, builders, engineers, the building industry, and regulators use NZS 3604 for practical guidance on how to design and build houses to meet New Zealand Building Code requirements, without the need for specific engineering design. NZS 3604 provides an Acceptable Solution in the Compliance Documents of the New Zealand Building Code. This means designs and plans in accordance with NZS 3604 are deemed to comply with the New Zealand Building Code and must be accepted by building consent authorities. This provides the sector with the most cost effective, efficient way for designing, building, and inspecting a house, which meets the performance requirements of the New Zealand Building Code.

Revision process

Many different stakeholders are involved in the NZS 3604 revision process. The organisational structure for the project has been broken down into three main areas: a leadership group, a technical committee, and five work groups have been established – loadings, bracing, durability, roof framing, and design clarity.

Overall, the leadership group and the technical committee agree that there is a need for a limited technical review of the NZS 3604. The ‘limited technical review’ will reflect the needs of industry, changes in materials and industry practice, and changes in related Standards including those setting requirements for loadings It will also incorporate content on bracings and durability.

Introducing the revision leadership group

Standards New Zealand has formed a leadership group of senior people in the building industry to maintain an overview of the entire review process for NZS 3604. As at June 2009, the group has met three times.

‘The leadership group is needed to provide guidance from all relevant industry sectors,’ says Derek Baxter, Chair. ‘This means the technical committee can focus entirely on technical issues surrounding the revision of the Standard.’

Representatives on the leadership group are:

• Derek Baxter (Chair), Chief Executive Officer, Certified Builders’ Association

• Don Bunting (Chair P3604 Technical Committee), Chief Executive Officer, Masterspec

• Pieter Burghout, Chief Executive Officer, Building Research Association of New Zealand

• Debbie Chin, Chief Executive, Standards New Zealand

• Len Clapham, Chief Executive Officer, Building Officials’ Institute of New Zealand

• Irene Clarke, Manager Environment and Regulation, Local Government New Zealand

• John Gibbs, Board of Directors, Architectural Designers’ New Zealand

• Ralph Hill, Chief Executive, Designers’ Association New Zealand

• Ruma Karaitiana, Chief Executive Officer, Building Construction Industry Training Organisation

• David Kelly, Deputy Chief Executive Building Quality, Department of Building and Housing

• Beverley McRae, Chief Executive Officer, New Zealand Institute of Architects

• David Middleton, Chief Executive Officer, Earthquake Commission

• Warwick Quinn, Chief Executive Officer, Registered Master Builders’ Federation.

Introducing the technical committee

The technical committee has been formed under Standards New Zealand's Standards development guidelines to enable the many different stakeholders to be involved in the NZS 3604 revision process. As at June 2009, the technical committee has met four times.

‘The technical committee is primarily responsible for focusing on and reviewing technical issues surrounding the revision of the Standard, and developing the revised draft,’ says Don Bunting, Chair of the technical committee.

The technical committee includes 22 industry representatives, nominated for their expertise in areas directly related to the revision of NZS 3604.

Representatives on the technical committee
Nominating organisation Technical committee member
Architectural Designers New Zealand Inc. Colin Hill
Building Officials’ Institute of New Zealand Colin Clench
Building Research Association Eddie Bruce
Building Research Association Roger Shelton
Cement and Concrete Association New Zealand David Barnard
Certified Builders’ Association New Zealand Richard Merrifield
Construction Information Limited Don Bunting – Chair
Department of Building and Housing Graeme Lawrance
Design Association of New Zealand Inc Allan Walters
Douglas Fir Association Scott Gibbons
Frame and Truss Manufacturing Association New Zealand Mark John Ash
Institute of Professional Engineers New Zealand Ernest Lapish
Institute of Professional Engineers New Zealand Ian Garrett
New Zealand Building Industry Federation of New Zealand Inc. Stephen Walker
New Zealand Institute of Architects Michael Middlebrook
New Zealand Institute of Building Surveyors Inc. Hans Gerlich
New Zealand Metal Roofing Manufacturers Inc. Stuart Hayman
New Zealand Timber Industry Federation Inc. Bruce Anderson
Registered Master Builders’ Federation Jamie O'Leary
Scion Research Douglas Gaunt
Window Association of New Zealand Inc. John Yolland
Wood Processors’ Association of New Zealand Warwick Banks
Key decisions/recommendations made to date

Standards New Zealand notified key stakeholders about the revision in 2008 and sought feedback. From the comments made, the technical committee has begun implementing changes needed in the draft Standard.

1. The revision of NZS 3604 is to proceed as a ‘limited technical review’ with the following scope:
2.
• AS/NZS 1170 Structural design actions – the loadings Standard – is referenced in the Compliance Documents to the New Zealand Building Code effective 1 December 2008. NZS 3604 needs to be updated to reflect AS/NZS 1170.

• Section 11. The building envelope, roof, and wall cladding
The majority of this section has been superseded by the compliance document E2/AS1 External Moisture. This section will be removed from NZS 3604.

• Section 4. Durability
Section 4 is to be updated to bring it in line with the recent changes to the Building Code and other Standards, in particular the maps and recent product developments.

• Section 5. Bracing design
The content is appropriate; however there are a number of problems with readability and some areas are too open for interpretation, which has the potential for inconsistency among building consent authorities. The committee is reviewing the usability and the appropriateness of worked examples, and so on. For example, subfloor bracing and interior bracing are to be re-evaluated.

• Section 10. Roof framing
The biggest issue concerns the design process, now roof trusses are designed and manufactured by producers. There are also other issues where the information is out of date and does not reflect current practice.

• Indexing and referencing, tables, diagrams, worked examples, and so on
All the feedback received suggested that the Standard has a good order and flow, however there is an opportunity to improve the indexing, referencing, and the usability and clarity of the diagrams and tables.

3. E2/AS1 is to be revised; The Department of Building and Housing will be running this project in parallel with the revision of NZS 3604.

4. Section 4 Durability is to cover structural issues only. All areas to do with the building envelope or weather-tightness are to be removed because they are now referenced in E2/AS1.

5. Section 19 Statutory information is no longer relevant and is to be removed.

6. The foreword is to be reviewed and updated. A draft has been tabled for discussion by the technical committee.

7. Several recommendations have been made by the loadings work group on AS/NZS 1170 including reviewing the soils determination process and soils classification, adding an extra high wind zone classification of 55 metres per second to NZS 3604, including reclarification of the wind zone and seismic maps to be adjusted to include reference points identifying where the zones start and finish. This is work in progress.

8. The durability work group has identified key issues including reclarifying the corrosion zone maps for sea spray zones, reviewing fastener treatments for higher weight galvanising, including identifying clauses 4.5, 4.6, 4.7, 4.9, 4.10, and tables 4.4 & 4.5 for deletion, among others.

9. The bracing work group is well advanced. It has made several recommendations to the technical committee, and is currently reviewing section 5 on bracing design, for relevant clause, table, and figure changes.

10. The roof framing and design appearance and clarity work groups have identified the key issues for consideration and are in the early stages of developing their recommendations to be put to the technical committee.

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ENDS

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