As with Terrain Category and Topography Factor, the Shielding Factor also plays an integral part in determining the site design criteria for a particular location. As the name suggests, it looks at structures that will potentially ‘shield’ your shed or garage from the wind.
This reduction factor is often misused and should only be used with caution. Always ensure that a suitably qualified and insured professional reviews your Site Classification as part of your approval process.
The relevant code specifically nominates that shielding from tress or vegetation is not permitted. Although shielding on one or a few directions can be a factor, apart from region A, it rarely is. That is, it’s either in all directions, or it’s not relevant. The value of Shielding varies from a reduction multiplier of No Shielding (1.0) to low as 0.7.
A factor of 0.85 should apply where at least two rows of houses or similar size permanent obstructions exist in all 8 cardinal directions. This would be for typical suburban development of 1000m2 (¼ acre) blocks.
When the engineer carries out a site specific design wind speed calculation, the shielding along with all other factors is considered in all 8 cardinal directions such as North, North-East, East and so forth.
There are 4 things to consider when looking at shielding;
1. Only buildings whose height is equal to or greater than the building being considered shall be deemed to provide shielding.
2. Shielding is considered only within the area of 20 times the average height of the building being considered.
3. Each cardinal direction must be considered individually.
4. If the slope of the terrain is greater than 0.2 (1:5), then no shielding is applicable.
The formula for calculating the shielding of a site specific building is quite detailed and requires an experienced and qualified professional. Consequently it is essential that an engineer completes a site specific design wind speed analysis before signing off on building plans.
All Wide Span Sheds’ steel buildings are designed to suit the site design criteria specifically. We put great importance on this, as it affects the safety of not only your investment, but the lives of the people who are in and around the shed.
To find out more about our extensive range of quality steel building solutions, please call one of our shed representatives today on 1300 94 33 77.