What is a Timber Frame
For a conventional house, a timber frame could be described as a skeleton of timber components to which would he attached wall claddings (the exterior skin), internal linings (the interior skin), flooring (the walked-on surface) and roofing (to protect the structure from rain etc.) and windows and doors.
Footings & Foundations
The building frame will usually be supported on piers, piles, stumps, posts or dwarf brick walls or perimeter masonry walls usually referred to as the sub-structure. The sub-structure in turn carries the load to the "footings" which according to local practice may be sole plates of durable or treated timber, or commonly, a concrete pad or a rectangular section reinforced concrete filled trench. Size of footings and spacing would be related to the size of the building. (hence the bearing pressure on each component of the footings), and on the nature of the soil/ground on which the footings rest. Such design information is now included in Australian Standard AS2870 Residential Slabs and Footings.
The majority of timber framed houses built in New South Wales in recent years have comprised timber wall and roof framing attached to a concrete slab-on-ground. Design details of a concrete slab-on-ground usually requires the services of a professional engineer to ensure that even the simple slab complies with the requirements of the approving authority. The new Building Code of Australia will "call up" AS2870 referred to above.
Allowance for Wind Loading & Earthquake
Most conventional housing in southern Australia is built in protected suburban regions where it is unusual to encounter winds exceeding 180 kph hence AS1684 can be used as a guide to design in such developed areas. This indicative regional wind velocity (180 kph) converts to a design wind velocity, on the once in 50 year return basis, to 33 m/sec. Where the approving authority or the owner requires that a design wind velocity exceeding 33 m/sec should be used in calculations, or, perhaps some resistance to earthquake activity is necessary, then, again, specialist design advice is required. These conditions would require reference to Australian Standard AS1170: Loading Code: Part2. Wind Forces and/or Australian Standard AS2121: Earthquake Code respectively.
In Timber Framing Manuals accepted in Tasmania, Victoria, Western Australia and Queensland, provision is made for a design wind velocity of 42 m/sec. In Queensland, manuals give information for higher design wind velocities.
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