Fig 1a Mixed materials
Fig 1b Masonry veneer
Fig 1c Unseasoned members
Fig 1d Clearance for unseasoned
members
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Allowance
for movement due to shrinkage
Allowance often needs to
be made for shrinkage and differential movement at
connections and in construction. Failure to do so may
lead to:
- Breakdown of the
building envelope, allowing ingress of moisture
- Unevenness in a
finished surface, such as a floor
- Splits, cracks or
gaps in flooring, door jambs, skirtings and
cornices
Measures which can be
taken to avoid this include:
- If timber is
unseasoned (e.g. floor joists), use species with
similar shrinkage values.
- Where timber is mixed
with steel and/or concrete construction, use
seasoned timber to minimise differential movement
(refer to Figure 1a).
- Joints and
connections should be detailed to allow seasoned
material to reach equilibrium inside the
building. This is especially important in heated
or air-conditioned buildings.
- Allow for vertical
movement in unseasoned framing by leaving
adequate clearance to the top of masonry veneer
(refer Figure 1b).
- Allow adequate
clearance at the top of unseasoned members fixed
to members that will not shrink (refer Figures 1c and 1d).
Reference: Timber Datafile
P4 – Timber – Design for Durability of the NAFI
Timber Manual.
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