STRUCTURALLY FIXED CAVITY BATTENS
BRANZ Bulletin BU 582: Structurally Fixed Cavity Battens
BRANZ have published BU 582 which updates and replaces BU 475 of the same name.
The reason this Bulletin is important is that for horizontal weatherboards, particularly Bevel Back weatherboards over standard vertical battens, fixings usually become very large to meet the 30-35mm penetration of the stud requirement of NZBC E2/AS1. For instance, to NZBC E2/AS1 a direct fixed Bevel Back needs a 75x3.15mm nail compared to a standard cavity batten fixing of 90x3.55mm. The extra length means a larger diameter and this can cause problems with splitting the weatherboard.
This can be overcome by using non-standard structurally fixed vertical battens which allows the use of smaller direct-fix type fixings. Although this would be an Alternative Solution it has been proved and confirmed by the BRANZ Test Report ST0589 Version 2 Fixing Horizontal Weatherboards to Studs Over a Cavity, which should make approvals for this easier.
The other advantage to this application is that if you are using expensive fixings (stainless, silica bronze etc), the smaller and slightly cheaper fixings can be used while the batten could use the larger/cheaper fixings.
In BU 582, BRANZ state that the structural battens should be H3.1 treated, which is the same as non-structural battens in NZBC E2/AS1. This raises the question of, as it is structural, should the batten actually be H3.2 treated to comply with Code? Masterspec would recommend specifying H3.2 battens in this situation, and it can be argued as good practice even in the standard non-structural batten situations.
As you would expect there are a number of limitations and requirements, but these are not out of the ordinary, refer to the BU 582 for details.
For those who are familiar with the old BU 475, the new BU 582 is largely not very different, with subtle additions like power-driven hot-dip galvanised nails for fixing battens now being allowed. However a small change which has wider ranging ramifications is the addition of a new section 4.5 OTHER CLADDING. BRANZ have confirmed that this section would cover the use cladding types other than horizontal weatherboards associated with vertical battens, for up to and including extra high wind zone. For cladding types that require a lot of expensive fixings or screw fixings, this may be quite useful.
Masterspec has updated sections that referred to BU 475 to BU 582 (BU 583 Waterproof Decks, issued at the same time and also updated). If you are interested in using structural battens we recommend getting a copy of this Bulletin.