Guidance on barrier design replaced the Acceptable Solution for timber barriers, B1/AS2, which was discontinued on 31 January 2012.
This information was confirmed as current in February 2016. It originally appeared in Codewords newsletters prior to January 2014.
The barrier guidance incorporates loadings from AS/NZS 1170, Structural Design Actions, and covers the range of materials now being used. Most barriers currently being built are of materials other than timber, such as glass and metal.
It replaced B1/AS2, which only provided a solution for timber barriers, based on loadings specified in the superseded NZS 4203:1992.
Guidance on barrier design addresses a range of areas including barrier geometry, loadings, deflection limits, and testing procedures to prove a design’s performance. It also provides information for barriers constructed of timber, glass and metals, and includes a useful checklist for building consent application checking at the end of the document.
It was developed by a working group of structural engineers and specialists from the design, manufacturing and construction industries, in consultation with a number of industry participants.
Domestic timber barriers that comply with the Barrier Guide comply with the Building Code
If a domestic timber barrier complies with the Barrier Guide as adjusted below, it also complies with the Building Code. It does not need further specific engineering design.
The Barrier Guide covers barriers made from all materials
The Barrier Guide was issued in November 2011, replacing Acceptable Solution B1/AS2, which provided only a timber barrier solution. The Barrier Guide provides helpful general guidance on barrier design, in recognition that more barriers are being constructed from materials other than timber.
Making sure domestic timber barriers comply with the Building Code
We’ve heard from building owners and designers that some Building Consent Authorities are requiring specific engineering design for timber barriers, despite them complying with Paragraph 4.2.7 of the Barrier Guide.
Building Consent Authorities are responsible for approving the barrier design. They are correct to note that the Barrier Guide does not automatically have to be accepted as Building Code compliant. However, some BCAs are requiring engineering justification, which adds considerably to the costs of the barrier.
A domestic timber barrier complying with all the recommendations of Paragraph 4.2.7 of the Barrier Guide does comply with the Building Code. The supporting deck must comply with Clause 7.4 of NZS 3604: 2011 and the 90 x 90 mm barrier posts must be at a maximum of 1000 mm centres (crs).
Adjustments to the deck details in NZS 3604
The deck details in Figure 7.10(c) of NZS 3604 require some adjustments because 250 mm M12 coach screws are not available. 240 mm long M12 coach screws are available and are suitable.
On the 'Plan View':
- At each strap location (at joist ends and nogs), two M12 240 mm long coach screws are required
- The words ‘2/M12 x 250 mm coach screws at 140 crs. vertically' should read ‘2/M12 x 200 mm coach screws at 140 crs. vertically’.
On the 'Section View at Nogging':
- The words ‘M12 x 200 mm coach screws at 400 crs. vertically’ should read ‘M12 x 240 mm coach screws at 140 crs. vertically. Detail also applies to joist ends.’
In conclusion, a domestic timber barrier that complies with Paragraph 4.2.7 of the Barrier Guide, with NZS3604:2011 Figure 7.10(c) adjusted as noted above, also complies with the Building Code. It does not need further specific engineering design.