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Following are questions which are frequently asked by customers, or
which address important issues which can affect satisfaction with a decking
project and are worthy of particular mention. Please follow the link to the
answer.
Why should fixings be placed in a staggered alignment?
Why are split joists a problem?
Why should I use wider joists?
Why should materials and construction methods be of good quality but also suitable for external
conditions?
Why should
fixings be placed in a staggered alignment?
Fixings placed in a nice straight line, certainly look
neat, but have a greater tendency to split the joist - in hardwoods, fixings
placed in a straight line will invariably split the joist - we are not sure if
this also applies to softwood joists. Fixings act like little
wedges, exerting splitting stresses on the joist. Where the fixings are
close to one another, such as where they have been placed in a straight line,
the splitting stresses can join up and the joist may have a split which runs
from fixing to fixing and which can be seen if you look between the deck
boards. (refer image below).
Staggering the alignment of the fixings increases the
distance between them so that the splitting stresses are unlikely to join up.
Why are split joists a problem?
Split joists are likely to result in:
a reduction or
total loss of hold-down forces, allowing movement and distortion in the
decking;
nails
“walking-out” of the deck as the decking moves under foot traffic (refer image
below); and
The possibility that joists may split from the stresses caused during fixing
of the deck can be significantly reduced by placing fixings in a formal
staggered alignment/pattern, offset by approximately 10mm
(approximately 5mm each side of the centerline of a wide joist). In
addition, joists should be pre-drilled when using large diameter or deformed
shank fixings to reduce splitting stresses or to allow hand nailing.
Why should I use wider joists?
Wider joists, ie 50mm unseasoned hardwood, 42mm seasoned hardwood or 45mm
seasoned softwood, should be used to allow the placing of fixings in a formal staggered
alignment/pattern, to reduce the likelihood of split joists, while also
maintaining the required edge clearance to avoid breaking out the side of the
joist. Wider joists are
also better for joining of decking boards over the joist. On a wider
joist, the fixings can be placed further from the end of the board, thereby
reducing the likelihood of the fixing splitting the end of the board. |
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Why should materials and construction methods be of good quality but also "suitable" for external
conditions?
The external environment has a severe effect on building materials and the
materials used in a fully exposed timber deck must not only be of good
quality but suitable for the application eg only hot dipped
galvanised bolts are both “quality” and “suitable” for external applications
- zinc plated bolts may be a “quality” product but they are not
“suitable” for external use as the zinc coating will corrode from the
surface quickly in contact with treated timber commonly used externally.
The unprotected surface will then rust quickly leading to premature failure.
Similarly, there are many different types of timbers available for decking with many
different preservative treatments.
LifePlus® Decking is only manufactured from “selected hardwoods” - high
quality, durability 1 (outside above ground classification to AS
5604 – 2003) hardwoods (with
sapwood preservative treated to hazard level H3)
with proven durability, stability and weathering characteristics
to deliver superior performance in weather exposed conditions. Note that
LifePlus® Decking is not produced from “mixed hardwoods”, which can be
supplied from a variety of hardwood species including some which are of lower
durability, higher shrinkage and lower stability than we would consider
acceptable.
Other "suitable materials" and practices include:
- Using only hot-dipped galvanised or stainless steel, (depending on
severity of exposure) bolts, brackets and nails (zinc
plated bolts and nails are not suitable for external use and brackets
manufactured from lightly lightly galvanised plate are not suitable for
fully weather exposed conditions. Stainless steel fixings shall be
used in corrosive conditions such as in coastal areas and around pools).
- Sealing any cut ends and housed joints with a timber sealer, consistent with
other finishes used.
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