information/FAQs

Plywood bracing - introduction and advantages

Historically, residential and other low rise buildings in Australia have regularly suffered wind damage. The personal and community costs, emotionally and economically, have been enormous. Wind damage is universal throughout Australia. Although the problem of wind design has been well accepted, in the tropical cyclone prone areas of Australia, wind damage from local thunderstorm or downburst activities cost millions of dollars annually. The latest version of the wind loading code AS1170 Part 2 - 1989 recognises this situation.

A simple system, called plywood bracing, utilising standard structural plywood panels nailed to the timber frame, economically and reliably reduces the risk of damage to buildings from wind forces.

A real benefit of the plywood bracing system is, while providing reliable structural adequacy, it allows for open planned design through the ability to provide bracing resistance in short wall lengths. The trend towards open planned living in Australian homes, to suit our amiable climate, was considered closely in the development of the plywood bracing system.

Buildings are vulnerable to wind damage at all stages of their life cycle. They are particularly vulnerable during the construction phase, especially if roofed with terra cotta or concrete tiles prior to the installation of wall linings or cladding, which is common practice. The installation of plywood bracing, prior to roofing, protects the building during this vulnerable period. It also protects the finished structure from damage from wind during its design lifetime of over 50 years.

Plywood bracing provides an engineered solution using thin structural plywood panels nailed to the timber frame, providing structural shear walls which resist the horizontal racking loads applied to the building by the wind. The plywood panels can be used also to provide resistance to wind uplift by connecting the roof to the subfloor.

The design information for calculating the details of the plywood bracing is provided in two formats:

The STANDARD SOLUTION covers the majority of building requirements in a simple manner. The standard solution follows the method detailed in AS1684.4-1999 Residential timber- framed construction; and.
The ENGINEERED SOLUTION or optimised solution which has been developed for building technologists, architects and engineers and provides an optimised design solution for all buildings including those outside the scope of standard solution.

Why Plywood Bracing?

The horizontal wind forces that are applied to the walls of a building at right angles to the wind flow, must be resisted by structural shear walls or diaphragms parallel to the wind flow. These shear walls must be sufficiently strong to prevent a complete structural failure, and be stiff enough to ensure the building does not rack too far out of square, thereby preventing cracking of rigid non structural wall linings or claddings.

Traditional timber framed dwellings utilised let-in timber braces at 45 to the studs to resist the horizontal wind forces. Modern buildings are generally larger in floor area, have bigger rooms, and larger and more numerous openings in external walls. Additionally, modern non-structural materials have replaced structural linings and claddings. These developments have combined to create a structure which is inherently less stable under horizontal wind loads.

Wall claddings and linings now provide less stiffness, and significantly less outside wall frame is available for the installation of 45 degree diagonal braces. In double storey construction, the wind loads applied to the lower storey, approach three times those on the top storey. In the bottom storey of such structures, conventional diagonal bracing is unable to provide sufficient resistance to the maximum wind loads the building may face during its lifetime.

Plywood bracing can overcomes this problem economically and reliably as it:

Provides structural adequacy with design flexibility;
Utilises short walls for bracing;
Is light and easy to install by simple nailing;
Can be machine (gun) nailed;
Does not incur edge damage during installation from nailing;
Provides resistance to impact and handling damage during installation;
With 'marine' bonded panels, performs structurally for the 50 year intended life cycle;
The system is incorporated in AS1684 Residential timber-framed construction and is approved by building and lending authorities;
Provides adequate bracing in lower storey of two storey construction;
Braces the frame at all stages of the life cycle of the building including the vulnerable construction phase;
Is compatible with normal timber framed construction; and
Provides earthquake resistance.

Reference: Plywood Association of Australia brochure; "Structural Plywood Wall Bracing".