Changes to H3.1 for solid timber framing - Notice
This is an important notice for framing specifiers. H3.1 treatment class is no longer an Acceptable Solution for solid timber framing.
In 2003, the review of NZS 3640 (Chemical preservation of Round and Sawn Timber) split H3 into H3.1 and H3.2. H3.1 was developed as a dedicated 'cladding treatment' class, and H3.2 continued for external structural timber not in ground contact.
Partly in response to the leaky building crises, H3.1 was adopted in 2003 for some enclosed framing use. However, in 2011 this was discontinued under B2/AS1 when all framing was cited as H1.2 (except for H3.2 cantilevered deck joists)
The discontinuance of H3.1 as a framing treatment allows it to revert to its original purpose as a cladding treatment class. B2/AS1 reinforces this in its 2014 amendment which states, under 3.2.3: '...Timber used for structural purposes is required to be durable in-service for the life of the building, being not less than 50 years unless ... This is applicable to H1.2, H3.2, H4, H5, and H6 ... Timber used for non-structural purposes, such as H1.1 and H3.1 is required to be durable in-service for a minimum of 5 years and 15 years respectively'.
H3.1 is no longer an Acceptable Solution for solid structural framing. H1.2 or H3.2 is required for enclosed framing under B2/AS1.
You can read more on the changes to H3.1 for solid timber framing on the building.govt.nz website(external link)