Your Met-Kit home will be given a wind rating that is determined by four main factors. These are the Wind Region, Terrain Category, Shielding Factor and the Topography of the land.
1. WIND REGION
This refers to where your home is or will be located. Region A – Normally refers to the southern half of Australia, with the exception of 100 km wide coastal strips on the east and west coasts, north of Coffs Harbour and Green Head. Region B – Intermediate refers to the 100 km wide coastal strip, which also extends around the northern half of Australia, except where there is a 50 km wide cyclonic coastal strip. Region C – Tropical Cyclones, refers to the 50 km wide cyclonic coastal strip extending around the northern half of Australia, except where there is an area of severe tropical cyclones on the west coast of Australia. Region D – Severe Tropical Cyclones refers to the coastal strip on the west coast, roughly between Carnarvon and north-east of Port Hedland. The main structural threat of cyclonic winds is the aerofoil factor where the roof is sucked upwards by air blowing across the roof line. Stronger tie-downs for the roof are combined with extra wall bracing, with sheet bracing sometimes added in critical parts of the frame.
2. TERRAIN CATEGORY
This describes the surface of the area up to 500 metres from your home site. TC 1 Very exposed and open, with few or no obstructions. Enclosed water surfaces. TC 1.5 Open water surfaces including near-shore water, large unenclosed bays, lakes and enclosed bays. TC 2 Open terrain such as farmland with isolated trees and grassland. TC 2.5 Terrain with a few trees or isolated obstructions. This terrain is typical of outer urban areas with scattered houses, or rural developments with few buildings per hectare. TC 3 Terrain with many closely-spaced obstructions, such as suburban housing or light industrial.
3. SHIELDING FACTOR
FULL SHIELDING – FS. This occurs where at least two rows of houses or similar-sized permanent obstructions surround the house being considered. Full shielding is typical of suburban developments greater than 10 houses per hectare. In Regions A and B of Australia, heavily wooded areas within 100 metres of the site provide full shielding. PARTIAL SHIELDING – PS. This requires at least 2.5 houses, trees or sheds per hectare. It’s typical of acreage-type suburban developments or wooded parkland. The second row of houses are classified as partially shielded. NO SHIELDING – NS. This applies where there are no permanent obstructions or less than 2.5 obstructions, such as houses, per hectare.
4. TOPOGRAPHY EFFECT
The topographic classification is determined by the effect the wind has on the dwelling, due to its position on the hill. A minimal slope such as the bottom of the hill or a less than 1-in-20 gradient would be classed as T0. A cliff is defined as a slope of greater than 1-in-3 and has the maximum topographic rating of T5 at the top. The maximum slope is measured at the steepest part of the hill, regardless of where the dwelling is positioned. Over the top of the hill, the wind pressures drop down.
5. WIND CLASSIFICATION
This wind classification system is a combination of wind region, terrain category, shielding and topography. The Australian Standard AS4055-2012 Wind Loads for Housing sets out 10 wind classes N1-N6 (non-cyclonic regions) and C1-C4 (cyclonic regions) Met-Kit homes uses the Paal framing system and designs all homes being built in non-cyclonic zones to a minimum wind classification N3. “This is even for regions that might require N1 or N2, so there’s a considerable safety margin,” said Paal product development manager Philip Weymouth. “We also build to the C2 rating for cyclonic zones.” “Because we design strong, the customer doesn’t have to worry, since we always meet or exceed the Australian wind loading standards.” “Mostly we can make an informed decision on all wind related factors by looking at the house plans, but if necessary we will refer a home builder to a local engineer for assessment of the block,” Philip said.
6. CSIRO TESTING
The structural integrity of the Paal steel framing system is a result of extensive in-house testing of the frames and roof trusses by engineers at the Paal factory in Emu Plains. This work has been followed by further strength testing of the frame and roof components by the CSIRO.