Understanding wind classification and why it matters for your building project

October 04, 2019

The wind classification for your site will play a critical role in determining what your overall design can look like. The wind classification of your site determines the amount of bracing, as well as the type of bracing, that your project will require. Wind classification covers three key areas of your build:

• roof bracing;
• wall bracing; and
• floor and sub-floor bracing.

It can also influence the type of tie-down between your:

• roof frame to wall frame;
• wall frame to floor frame;
• your floor frame to the sub-floor structure; and
• the sub-floor structure to your pad/strip footing or slab.

Defining wind classification

But what exactly is wind classification? And why does it matter in building projects?

Wind classification is the term used by building engineers and other construction professionals to measure the gust wind speeds (m/s) that affect a given site. Wind classification is determined by the wind speed at a structure, which in turn is influenced by the terrain the wind flows over as it approaches the structure.

Wind classification of a building site is critical for every building project as it helps to ensure that a building or structure is designed and built to a level that is appropriate to safely withstand the wind forces it will be subjected to.

Assessing and determining the wind classification for your site ensures that your project is designed and built to the installation standard that will ensure it is not structurally compromised in instances of high wind.

How your wind classification is determined

There are four key areas that your building engineer or designer will take into consideration when determining the wind classification of your site: wind region, terrain category, shielding, and topography.

1. Wind region

Your designer will locate your site in relation to its wind region. The different wind regions in Australia are defined as:

• Region A (Normal): Coffs Harbour and south NSW.
• Region B (Intermediate): North of Coffs Harbour (NSW), Gascoyne Junction (Western Australia).
• Region C (Tropical Cyclones): Bundaberg, Hervey Bay (Queensland), Northern Territory, and parts of Western Australia.
• Region D (Server Tropical Cyclones): Port Headland to Carnarvon, Western Australia.

2. Terrain category

The terrain category describes the surrounding area 500m from your building site. The wind speed when it reaches your structure will be affected by what obstructions it flows over as it approaches your house. Terrain categories range from TC1 (very exposed open terrain – no obstructions) to TC3 (suburban housing to light Industrial – lots of obstructions).

3. Shielding factor

The shielding factor takes into consideration the surrounding area 500m from your building site, and can be influenced by obstructions such as other houses or thick tree or wooded areas. Shielding factors range from full shielding (in the middle of suburban housing) to no shielding (no surrounding permanent structures).

4. Topography

The final key factor in determining the wind classification of your site is topography. Your topography classification is determined by the effect the wind has on your house according to its location on a hill, and the hills height and slope.

Combining these four categories will determine the wind classification for your site, which in turn will determine both the type of bracing and the amount of bracing that your project will require.

At Spantec Systems, our design and engineering team works with you to understand your building site and to determine its wind classification. From there, our experts will advise on the bracing that your project requires.

Need help with your next building project?

 For nearly 30 years Spantec Systems has been pioneering the use of light steel flooring systems, including structural steel beams and adjustable steel piers under sub-floors, for building professionals, owner-builders and DIY-ers. To find out how we can help with your next build, contact us on (02) 4860 1000 or by sales@spantec.com.au. Already have plans and engineers drawings? Then get a quote now.