Wind Load and Water Ratings
Why are wind load and water ratings important?
- Every site for every building in Australia should be assessed for wind load requirements according to AS/NZS 1170.2 Wind Actions or AS 4055 Wind Loads for Housing (a simplified document for housing).
- The wind loads are a deciding factor for the type of window and door system that will be used as they need to structurally withstand the loads that are present on the site.
- The two loads are Serviceability Limit State (SLS) and Ultimate Limit State (ULS). They are given in AS 2047 or calculated from AS/NZS 1170.2 or, if the construction is housing, AS 4055 can be used to obtain the N or C ratings.
ULS - Ultimate Limit State
To satisfy the ultimate limit state, the structure must not collapse when subjected to the peak design load for which it was designed.
SLS - Serviceability Limit State
To satisfy the serviceability limit state criteria, a structure must remain functional for its intended use subject to routine /everyday loading, and as such the structure must not cause occupant discomfort under routine conditions.
There are two Australian Standards that are used to determine wind loads for a building: AS 1170.2 Structural Design Actions and AS 4055 Wind Loads for Housing. As its name suggests AS 4055 may only be used to determine wind loads for “housing” which has a specific meaning under the code – only building classes 1 & 10 (a house and a garage/carport) within specific geometric limits may use AS 4055: all other building classes 2 through 9 must use AS 1170.2.
"Every site for every building in Australia should be assessed for wind load requirements "
For building classes 2-9 or houses that fall outside the geometric limits of AS 4055, AS 1170.2 must be used to determine the wind loads. A qualified, practising engineer must be engaged to apply this standard. The engineer will work out the ULS & SLS pressures specific to a building in a particular location.
No matter which standard is used, the window fabricator will use these ULS & SLS values to determine the strength of mullions and meeting styles and the relevant water penetration performance. It is vital that windows and doors are correctly specified in accordance with AS 4055 or AS 1170.2 to prevent non-compliance and the failure of these building elements.
AWS has developed a range of windows and doors suitable for extreme weather environments, Cyclone regions C & D.
Understanding wind loads & their potential to impact on a building will help us design & specify appropriate products to ultimately
- Safeguard people from injury caused by structural failure.
- Safeguard people from loss of amenity caused by structural behaviour.
- Protect other property from physical damage caused by structural failure, and
- Safeguard people from injury that may be caused by failure of, or impact with, glazing.
Under the Building Code of Australia all window and door manufacturers are required to produce windows and doors that meet mandatory minimum specifications under Australian Standard (AS) 2047- including AS1288.
Windows made from Timber, Aluminium, or other materials must undergo a series of performance tests to verify product performance claims to AS2047, one of these tests is AS4420.5 Water Penetration Resistance (WPR) Test – to verify that no water leaks through the window in to the building.
Water penetration levels are specified in AS 2047 - Windows in buildings and are set at pressures up to 30% of the SLS wind pressure. AS 2047 requires that windows undergo a water penetration resistance test where a large volume of water is sprayed onto the test window under an applied test wind pressure. The window must withstand the test for 15 minutes, without water coming in over the internal sill.
AWS has conducted all testing in a NATA accredited testing facility in accordance with the Australian Standard AS4420.0 – 1996 – Windows-Methods of test.
It should be understood that the test conditions do not reflect real life conditions. The test does not try to replicate a rain storm or cyclone. The test pressure is held constant for the entire 15 minutes, whereas real wind fluctuates (gusts) greatly. In many instances the product was simply asked to perform in excess of what the product was designed & tested to withstand.
In the case of an extraordinary weather event, windows & doors would be unable to be designed & tested for every conceivable set of weather conditions.