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Construction
Systems
Footings
Unreinforced concrete pad footings
are commonly used to support decks. Design requirements are
contained in AS2870 (see note 2) and AS1684 (see note 3). The
initial step is to determine the classification of the site. This
and footing sizes should be sought from the above documents or via a
structural engineer.
Posts
Hardwood posts are
usually unseasoned and commonly come in cross sectional sizes of 100
x 100mm or 125 x 125mm. For posts, the common stress grades fall in
the range of F11 to F22, all providing adequate load carrying
capacity.
Bearers & Joists
Bearers and joists
are available in a wide range of species, grades and sizes.
Unseasoned bearers usually come with a fine sawn finish, while
seasoned timbers are accurately thicknessed and dressed. Tables 1
and 2 provide guidance on the common sizes and
spans.
Structural Joints
Joints between posts and
bearers must efficiently transfer load. Notching posts as shown in
Figure 1 is one method of achieving suitable loadbearing capacity.
Care must be taken to ensure the notch depth does not compromise the
strength of the post (refer AS1684 (see note 3) span
tables).
Notes
2. AS2870 Residential
Slabs and Footings, Standards Australia, Homebush.
3. AS1684
Residential Timber Framed Construction, Standards Australia,
Homebush.
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