For structural steelwork and cold-rolled steel purlins and girts, refer to Specification for
Levels
It is critical that all floor framing is level. Before commencing the set out, check that slab or timber floor framing is level. It may be necessary to pack the frames in the low areas or to rectify the high areas.
Dimensions and Squareness
Check the position and square of the concrete slab or footings before commencing construction. Measure diagonals to check square.
Setting Out
When setting out the wall framing, a small error in position can lead to misalignment of the other components, such as the roof. Base the set out on the longest side of a building, since this will reduce the likelihood of errors in squareness.
Prefabricated Trusses
If there are setting out errors in the walls, there is a possibility that roof trusses may fail to engage the required supports. In complicated buildings, check the position of walls, before constructing the roof. It is critical that all wall framing be fixed and braced plumb.
Bracing and Tie-Down
All buildings must be adequately supported against lateral wind loads, as specified in AS 1170.2 and AS 4055. In some cases, lateral earthquake loads may be a design criterion. The bracing requirements should be determined for the appropriate Region, Terrain Category, Topography and Shielding and recorded on the drawings by the design engineer.
Tie Down
All buildings must be adequately tied down to resist overturning due to wind loads, as specified in AS 1170.2 and AS 4055. The tie-down requirements should be determined for the appropriate Region, Terrain Category, Topography and Shielding and recorded on the drawings by the design engineer. Ensure that all tie-down systems are continuous to the footings or to the specified location on the structure. AS 1684 and AS 3623 give requirements.
Corrosion of Galvanised Steel Posts
Where soil with a high salt content is allowed to cover the lower part of galvanised steel posts, it may cause them to corrode. To prevent this, encase the lower part of the post in 300 mm diameter concrete pedestal, 100 mm high with a sloping top. Occasionally inspect the footings to ensure that soil is not in contact with the steel.
Shrinkage
The following information in drawn from a number of references, including the following:
• Anon (1989), Introducing Timber – An Introduction to Wood and Timber, Timber Development Association (NSW) Ltd, Timber Information Leaflet No 1
• Anon (1997), Decorative Floors – Guide to Decorative Floors of Timber, Timber Development Association (NSW) Ltd, Timber Information Leaflet No 4
• Anon (1997), Hardwoods – Native hardwoods of the East Coast, Timber Development Association (NSW) Ltd, Timber Information Leaflet No 18
• Anon (1974), Technical Timber Guide - Shrinkage, TRADAC
• AS 1684.2 Residential timber-framed construction, Standards Australia
As timber dries, it shrinks, and in some circumstances cracks can open. The moisture content varies with type and the degree of seasoning. Seasoned timber has moisture content in the range approximately 10% to 15%, and a variation of up to 2% within any lot of timber.
Dense close-grained hardwoods dry more slowly than softwoods. The following table is available in TRADAC guide No 9. It sets out the mean percentage shrinkage in a lineal dimension from green to 12% moisture content. This table enables the specifier to determine which timbers are most likely to present the greatest potential shrinkage problems.
Notes:
1. Tan means in the tangential direction. Rad mean in the radial direction.
2. Tasmanian Oak is a mixture of Alpine Ash and Mountain Ash.
AS 1684 Appendix F has the following requirements for timber flooring, in respect of limiting shrinkage.
| Climate Zone | Average Indoor Equilibrium Moisture Content % | Seasonal Equilibrium Moisture Content Range % | Recommended Average Moisture Content at Installation
|
| Coastal (Zone 3) | 12% | 10% to 15% | 12%
|
| Inland (Zones 1 and 2 | 9% | 7% to 12% | 9%
|
| Air-conditioned | 9% | 7% to 12% | 9% |
