Issue 24 – February 2011
Standards New Zealand has just published NZS 3604:2011 Timber-framed buildings. NZS 3604 provides guidance to builders, architects, engineers, designers, and students for the design and construction of timber-framed structures not requiring specific engineering design. The Standard is a core resource for building consent authorities determining compliance with the New Zealand Building Code.
A limited technical review of NZS 3604 commenced in 2009. The project was sponsored by Standards New Zealand, Earthquake Commission, and the Department of Building and Housing with support and input from a leadership group and technical committee including a range of stakeholders from various industry sectors.
Standards New Zealand formed a leadership group to maintain a strategic overview of the NZS 3604 revision project and to provide policy guidance from relevant industry sectors. The leadership group included 13 representatives from key organisations in the building industry.
'Building Standards have a proud history in New Zealand and they have recently been challenged by nature and confirmed,' says Derek Baxter, Chair of the NZS 3604 leadership group and Chief Executive Officer, Certified Builders' Association.
'Throughout the NZS 3604 review there were parallel work streams occurring elsewhere, including the review of the New Zealand Building Code, changes to E2- AS1, and matters arising from the Canterbury earthquake. The output from these work streams needed to be considered and kept in context, and aligned to the revision of NZS 3604.
'For the first time, Standards New Zealand used a leadership group to help keep us in touch with all of the parallel work stream activity and to allow the work groups to do their specialist work.'
Limited technical review brings NZS 3604 up to date
A technical committee was also formed to focus on the technical review and to update content in NZS 3604. The technical committee included 22 people representing the following organisations from across the building industry:
- Architectural Designers New Zealand Inc. – Colin Hill
- BRANZ – Eddie Bruce and Roger Shelton
- Building Officials' Institute of New Zealand – Colin Clench
- Cement and Concrete Association New Zealand – David Barnard
- Certified Builders' Association New Zealand – Richard Merrifield
- Construction Information Limited – Don Bunting
- Department of Building and Housing – Graeme Lawrance
- Design Association of New Zealand – Allan Walters
- Frame and Truss Manufacturers' Association of New Zealand – Mark Ash
- Institution of Professional Engineers New Zealand – Ernest Lapish and Ian Garrett
- New Zealand Building Industry Federation – 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 – Bruce Anderson
- Registered Master Builders' Federation – Jamie O'Leary
- Scion – Doug Gaunt
- Window Association of New Zealand – John Yolland
- Wood Processors' Association of New Zealand – Warwick Banks
The leadership group and technical committee approved a limited technical review of NZS 3604. Five industry-specific work groups reviewed specific sections of NZS 3604 and developed the revised Standard.
'While the project was described as a 'limited technical review', the word 'limited' describes the breadth rather than the depth of issues addressed,' says Don Bunting, Chair of the technical committee. 'Aligning NZS 3604 with AS/NZS 1170 Structural design actions, reflecting current industry knowledge around soil bearing capacity, bracing, durability, and the use of new building techniques, were all significant tasks.
'The creation of individual work groups – loadings, bracing, durability, and roof framing – ensured that all topics were given appropriate weight before being referred back to the technical committee.'
'Public comments received at the start of the project and about the draft Standard were both helpful and positive. These comments helped us to revise NZS 3604 to reflect the current and future needs of the construction industry.'
Public comment on the draft revised NZS 3604 closed on 7 April 2010 and all comments were collated for the committee to consider, before a final version of the Standard was prepared for postal ballot on 7 September 2010.
Following the Canterbury earthquake on 4 September 2010, we extended the NZS 3604 postal ballot period to give technical committee members working on the Canterbury earthquake more time to consider the postal ballot draft. The postal ballot phase concluded in December 2010 with technical committee members reaching consensus.
Since the Canterbury earthquake there has been much discussion on liquefiable soils and lateral spread across the sector and among the NZS 3604 leadership group and technical committee. The Department of Building and Housing (DBH) and Standards New Zealand have agreed to consider amendments to the revised edition of NZS 3604 or other documents when information and evidence about liquefaction and lateral spread is clear.
Note: DBH issued a document in December 2010 to provide guidance on the repair and rebuilding of houses in earthquake affected Canterbury. Guidance on House Repairs and Reconstruction following the Canterbury earthquake is available at www.dbh.govt.nz/guidance-on-repairs-after-earthquake.
Overview of the changes to NZS 3604
The 'user friendliness' of the original Standard's format has been retained in the revised document, and improvements to the layout and presentation of figures and tables have also been made.
In addition to updating NZS 3604 to reflect changes in building practices over the past 10 years, the limited technical review has encompassed the following:
- The AS/NZS 1170 Structural design actions Standards series is referenced in clause B1/VM1 under the New Zealand Building Code (NZBC). NZS 3604:2011 has been updated to reflect the provisions of the AS/NZS 1170 Structural design actions Standards series.
- Section 4 on durability has been brought into line with the NZBC. Text has been added on recent product development, durability of fixings, and adjustments made to the exposure zone maps.
- The coverage of bracing in section 5 has been reviewed to improve readability and to clarify requirements where our users have indicated value could be added.
- The Department of Building and Housing's Acceptable Solution E2/AS1 has superseded section 11 in the revised NZS 3604. With E2/AS1 being updated and extended in parallel with NZS 3604:2011, the original content of section 11 has been replaced by a small section addressing the interface between NZS 3604:2011 and E2/AS1. Accordingly, all design information on cladding has been removed from NZS 3604:2011.
- Requirements have been added on new building techniques and materials, in particular engineered timber products and trussed roof framing now commonly used in buildings. Read about further details on the changes, and comprehensive Q's and A's here.
Referencing in NZBC intended
The Department of Building and Housing has consulted on an amended B1/AS1, referencing NZS 3604:2011, and an amended E2/AS1.
These documents have been developed to work together and, subject to final decisions following consultation, the Department intends to issue them at the same time, in mid 2011. The amended documents are intended to take effect as soon as they are published. In the meantime, designers would need to present designs using NZS 3604:2011 as alternative solutions when seeking building consent.
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Related Touchstone articles
- Update from Debbie Chin, February 2011
- Postal ballot for revised NZS 3604 timber-framed buildings Standard reaches consensus, December 2010
- Update from Debbie Chin – update on revised timber-framed buildings Standard, November 2010
- Revised timber-framed buildings Standard issued for postal ballot, October 2010
- Revised timber-framed buildings Standard NZS 3604 – postal ballot, August 2010
- Revised timber-framed buildings Standard NZS 3604 – public comment completed, June 2010
- Revised timber-framed buildings Standard NZS 3604 – REMINDER public comment closes 7 April 2010, April 2010
- Draft timber-framed buildings Standard NZS 3604 – public comment reminder, March 2010
- Revision of Timber-framed buildings Standard NZS 3604 – public comment to start in December 2009, December 2009
- Timber-framed buildings Standard NZS 3604 – myth busting, August 2009
- Revision of Standard for timber-framed buildings NZS 3604 – work groups' update, July 2009
- Revision of Standard for timber-framed buildings NZS 3604 – technical committee and review update, June 2009
- Revision of Standard for Timber-framed buildings NZS 3604 – leadership group update, May 2009