Description and Purpose
The bracing system uses structural plywood of various types to provide sheet bracing for walls and subfloor foundations in both internal and external applications. The purpose of the system is to provide bracing resistance for light timber framed buildings under wind and earthquake loading, to meet the requirements of the New Zealand Building Code Section B1 Structure, and B2 Durability.
Ply will provide bracing for buildings designed and constructed in accordance with NZS3604 and for buildings that are specifically designed. It may be both a bracing and a wind barrier, and both a bracing and a cladding.
Structural plywood is manufactured to comply with the joint Australian/New Zealand Standard AS/NZS2269: 1994, “Plywood – Structural”. Sheets are branded in accordance with the standard.
Structural plywood is manufactured from Pinus radiata veneers bonded with phenol formaldehyde resin adhesive. Untreated Ply structural plywood may be used for dry interior exposure. For exterior use or internal environments exposed to high humidity or condensation, Use H3 treated Ply where the moisture content of the plywood or timber next to it could exceed 18% moisture content (e.g. wet area walls, foundation walls in subfloors, behind stucco).
The basic bracing sheet is 7mm thick 3 ply, DD grade in 2400mm and 2700mm long sheets.
The durability of plywood bracing applied exceeds 50 years.
Rain Wetting and Construction Bracing
Some materials used in bracing elements will not withstand exposure to weather. Untreated plywood sheets will withstand some rain and exposure during construction. Hence plywood bracing may be used as both construction and permanent bracing.
Humidity and Condensation
In uses where the moisture content of wood may exceed 18% for prolonged periods, plywood must be H3 treated to resist decay or insect hazard.
Subfloor Sheet Bracing
H3 treated plywood can be used unpainted as sheet bracing where dampness does not allow the use of untreated plywood or other sheet materials (clause 5.4.3 of NZS3604). Where plywood subfloor sheet bracing is exposed to both rain and sun, it should be coated with a three-coat acrylic paint system as for claddings.
Cladding and Bracing
H3 treated plywood can be used as cladding and bracing. To achieve 50-year structural durability, it should be at least five ply plywood and must be coated with a maintained three-coat acrylic paint system, preferably in a light colour.
Use corrosion resistant fasteners appropriate to the expected life cycle exposure for the bracing element.
Plywood (untreated or H3 treated) must not be allowed to come in contact with soil.
For further information, refer to the CHH Ply Durability Statement.
Use any one of the following fasteners with 7mm plywood:
For 9mm plywood use minimum length 40mm.
For 12mm plywood use minimum length 50mm.