The deck - preparation and laying
Preparing the deck
If the substrate is unfit for laying boards onto directly, the surface will need to be removed. When laying decking, it is important to remember that the decking board will
absorb moisture if in contact with water. Any moisture trapped within the roof will cause board movement and possibly joint failure. As with laying the laminate, ensure that
conditions are dry before decking the roof.
After removing the old decking, check that all roofing joists are sound and free from rot. Replace these as required. If possible,
build a fall into the substrate so that the roof can drain completely and remain free from standing water.
Firrings added to aid run-off >
Why use OSB3 boards?
- 2.4m X 0.6m X 18mm Tongue and Grooved boards.
- Designed to minimise expansion and contraction.
- Easy to handle & carry up ladders.
- Doesn’t need edge support between joists.
- Doesn’t require the joints to be bandaged.
Laying the deck
18mm OSB3 boards are laid lengthways at 90° to the roof joists. The boards must be laid with the writing side uppermost. Not only does this give a better key for the laminate, it also allows the resin to flow into the board joint to effectively glue the boards together.
Start to lay the boards at the furthest edge from the drip. If the board is laid along a wall, an expansion gap of 25mm should be left. Align the end of the board with the
fascia, laying following boards from end to end. Trim the last board in the row flush with the fascia. Using the off-cut (if greater than 400mm,) start to lay the next row of
boards by fitting the tongue firmly into the groove of the row already laid. The boards are now staggered and bonded and will form a strong deck.
When two rows have been laid, the boards can be aligned to run straight, fixing them as you go. Continue to lay each row in turn using the off-cut from one row to start the next row. The last row is simply cut off in line with the fascia.
It is essential that the deck is laid correctly. A poorly laid deck may result in porosity in the laminate.
When fixing the boards to timber joists, the most efficient way is to use a compressed air or gas powered nail gun, it also minimises damage to the ceiling below. A 63mm (or longer) galvanised ring shank nail should be used at 200mm centres, usually 4 nails across a 600mm board. The nails must be driven into a joist.
Some installers may wish to use screw guns. This is acceptable providing the screws have a minimum of 40mm penetration into the joist. The boards can also be nailed using a hammer. This is obviously time consuming and will probably lead to internal damage of the ceiling. All ring shank nails must be non-rusting (galvanised or sheradised).