A revised version of the Australian standard as4055 Wind Loads for Housing has been released and is now in force.
The standard provides a process by which wind loads can be determined for houses that fall into the dimension limits imposed by the standard.
One important addition to the new standard states that if wind loads are determined using this standard then only parameters from this standard can be used. This aims to stop the use of parameters from as1170.2 when an advantage might be gained.
The design gust wind speeds have not changed for cyclone and non-cyclone areas, however the terrain categories have been expanded with the addition of a terrain category 1.5. The current standard had categories 1, 2, 2.5 and 3, while the new standard has categories 1, 1.5, 2, 2.5 and 3. This has also caused the revision of the wind classification table to allow for the additional terrain category.
The process for selection of topographic class has been expanded and the selection of shielding class has been altered, with vegetation and trees specifically excluded as shielding elements in cyclone areas.
There is a new section included in the calculation of pressures and forces, which will help to define the location and size of pressure zones on roofs and walls. The lack of definition in the old standard caused some controversy because it provided scope for “interpretation”.
The tables of pressure coefficients have been expanded so that pressures resulting from the new standard process are slightly smaller in magnitude than the pressures specified in the current standard.
The effect of the lower wind pressures will be to permit the use of glass on greater areas where wind load is the controlling parameter for size. However, if human impact safety criteria are the controlling parameters then the glass areas will not change.
Compliance with any standard can only be claimed if all relevant sections of the standard have been satisfied.