New Zealand's main standard for the design and construction of timber-framed buildings, NZS 3604:2011 Timber-framed buildings, is being revised. The standard has a significant influence on houses being constructed in New Zealand, as it is a core resource for designers and building consent authorities determining compliance with the New Zealand Building Code (NZBC). The standard also gives guidance to builders and others involved in the construction of light timber-framed buildings.
MBIE’s Building Performance team commissioned a review of this standard and is funding its revision. Building Performance aims to help streamline the process of designing and consenting higher-density housing. The revision also aims to support the Building for Climate Change programme by improving the operational efficiency of buildings and improving the health and wellbeing of their occupants.
There will be a very specific scope for the revision. In early 2020, a scoping workshop recommended the scope of the revision of NZS 3604. The workshop assembled a range of relevant stakeholders to decide which specific areas needed changing in the revision of NZS 3604. Their proposed scope was then released for a period of public consultation and the feedback was reviewed at a second workshop.
The revision will also look to streamline the construction of several other design features that are commonly consented. More details on the specific areas that this revision project will address are detailed in the Appendix at the end of this article.
Standards New Zealand is now in the process of forming a standards development committee. It is anticipated that technical working groups will be established to provide advice on how the scope items above should update the draft standard. We would like to invite technical experts interested in participating on working groups to register their interest at this link.
The new standard is expected to be delivered just under three years from now, in 2023. Once published, it is expected to be incorporated into the building code.
Future updates on the revision will be published in the building section of Touchstone and in Building Performance’s The Wrap Up. Please also subscribe to our Touchstone newsletter or to The Wrap Up to stay informed.
The following specific areas will be looked at as part of the revision to NZS3604:
1. Facilitating better thermal performance: Focus on ways that revising NZS 3604 will support better thermal performance as part of New Zealand’s commitment to reducing greenhouse gas emissions by 2050.
2. Extending the scope to three full storeys within the standard: Expand the scope of the selection tables within the standard to address the increasing demand for medium-density dwellings with up to three storeys.
3. Foundations on expansive soils and on liquefaction-prone soils: Add foundation solutions to NZS 3604 for when the soil supporting a building is prone to either expansion or shrinkage. This feature will extend the November 2019 amendment to B1/AS1 of the NZBC that added solutions for expansive soils from the Simple House Acceptable Solution into NZS 3604. Add solutions for foundations on soils with medium liquefaction vulnerability into NZS 3604. These will target sites that are similar to those classified as TC2 in accordance with the MBIE document Guidance on repairing and rebuilding houses affected by the Canterbury earthquakes.
4. Steel bracing elements for wide openings: Include steel elements into this timber-based standard that can be used to support the framing above wider doors and windows.
5. Support details for long-span beams and lintels: Provide support details for proprietary elements such as beams, lintels, and trusses, which apply higher point loadings than can be supported by the current version of NZS 3604. It aims to provide simpler support solutions for a range of situations. It will include connections and foundation details.
6. Framing around internal stairwells: Extend the framing span tables and provide construction details for wall framing around stairwells that extends into a second storey. It will also introduce selection tables and construction details for framing within part-height internal barrier walls.
7. Isolated internal masonry walls: Add standardised construction details for isolated internal masonry walls. This will cover construction of hybrid structures that have a small number of internal masonry walls in a predominately timber-framed structure.
8. Revising a number of noted corrections and updates: Make a large number of minor corrections and updates that have been identified since NZS 3604:2011 was published.
9. Bracing: Create a new part (NZS 3604.2) that sets out how to determine both wind and seismic bracing for Subfloor bracing; Walls; Isolated masonry walls; and Steel bracing elements used in wide openings. Create new sections with bracing rating tables and construction details.