BRANZ Guideline May 2009

Reproduced from BRANZ Guideline May 2009

Supplementary protection to cut surfaces of treated timber

NZS 3602:2003 Clause 106.2 (timber in contact with ground, to achieve 50 year durability) requires house piles and poles to be treated to H5, and any cut or bored surfaces shall have in situ treatment in accordance with NZS 3640. It is also a requirement of NZS 3604 clause 6.4.3.3.

NZS 3640:2003 Informative Appendix B5 (Machining and sawing treated timber) says it is advisable to apply supplementary protection, as prescribed by the manufacturer, to H3.1 and higher timber, if cut or machined after treatment. Appendix B5 is recommended practice, and Clause 1.2.4 (Definitions) clarifies that the term "informative" identifies information provided for guidance or background but that does not form part of the mandatory requirements. Hence, it is not a mandatory requirement to apply supplementary protection to cut ends of H3.1 treated timber.

Painted or stained timber weatherboards must always have cut ends sealed before installation.

Skillion roof timber ceiling batten treatment

Under NZS 3602 Table 1D.3 radiata pine timber ceiling battens installed in low slope skillion roof construction (under 10º) where the ceiling lining is a structural diaphragm must be treated to H3.1 to achieve a not less than 50 year durability.

Windows and drained and vented cavities

Under E2/AS1, aluminium windows installed into a wall cladding system installed over a drained and vented cavity system can have the window sill and jamb flanges installed firmly against and sealed to the wall cladding materials. Any water that might get in and need to be drained can be managed by the cavity.

However, where a direct fixed cladding system is being installed, there must be a 5 mm gap between the back of the sill flange and the cladding to allow water that might get in to drain from the sill tray flashing. The jamb flanges can be sealed to the cladding using a method that will effectively seal but maintain the 5 mm gap – commonly done with a 12 mm wide sealed cell compressible PVC foam strip complying with paragraph 9.1.10.7 of E2/AS1.

Light reflective value (LRV)

E2/AS1 paragraph 2.4 specifies a light reflective value (LRV) of 40% or more for [Exterior Insulation and Finish systems] EIFS and flush-stopped texture coated fibre-cement claddings to minimise the risk of thermal movement resulting in cracking and the potential for water entry.

Specifying a light colour on all cladding will significantly reduce the amount of heat absorbed by the cladding and the resultant thermal movement.

Stair dimensions

Acceptable Solution D1/AS1 classifies the types of stairs that might be permitted in buildings and gives the pitch limits and the dimensional requirements for risers and treads of each.

Information on stair design and construction is also given in BRANZ Bulletins 495 Stair design and 487 Stair constructions.

Ground clearances for timber slatted decks

How close to the ground can a deck be built? If following NZS 3604, the minimum pile height above the ground is 150 mm with a DPC. However, for a number of existing and new buildings, once the bearer and joist depth is added, the timber slatted deck may be higher than the floor level inside the building.

Even though a deck close to the ground doesn't require a building consent, its construction must comply with the Building Code – in the case of a low deck, it is primarily the durability of the timbers used and structure. Any timber in ground contact (even if sitting on a concrete pad at ground level) must be treated to H5, while decks that allow a gap between the timber and the ground can be constructed using H3.2 treated timber.

Options to allow a low deck to be constructed can include:

  • bolting bearers to the sides of piles
  • supporting joists directly on concrete pads (using H5 treated timber and installing a DPC between the timber and the concrete is recommended) – some form of connection of the timber to the concrete, such as corrosion-resistant metal brackets or cast-in bolts, will need to be provided
  • bolting joists to cantilevered metal brackets embedded in a concrete pad to allow the timber to be supported clear of the ground (for this type of installation, decks should be attached to the building to provide lateral stability and therefore should be no wider than 2.0 m). When wider than 2.0 m some form of lateral support will need to be provided to stiffen the deck construction such as an anchor pile.

Suitable decking timbers

The main reference when selecting suitable timber for decking is NZS 3602 Table 2A7. When timbers other than treated Radiata pine (cypress species, vitex, kwila, eucalyptus or beech) are being considered, the timber must be heart timber to give the required minimum durability of not less than 15 years.

Also, if imported timber is being used for decking, ascertain whether it is from a sustainably managed source.

Published in building.