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How to Lay Boards

How to Lay Boards

How to Lay Flat Roof Boards

Step 1 How to Lay, Boards,


OSB3 Tongue & Groove ( Oriented Strand Board ) is the roof deck of choice for laying a new fibreglass roof. Its rough-textured surface allows the resin to get a firm grip and key into the board, meaning there is very little chance of delamination (the matting peeling away from the surface of the wood). Standard square edge boards allow 3mm gaps between adjoining boards for expansion.

Preparing the deck

If the substrate is unfit for overboard onto directly then 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 a 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.

Laying the deck

2400 X 600 X 18mm OSB3 tongue and groove boards are laid 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, but 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 the 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.


Fixing the deck to different substrates


When fixing the OSB3 board to timber joists, the preferred method is with compressed air or a gas-powered nail gun. This is the most efficient way of fixing the decking; it also minimises damage to the ceiling below. A 63mm (or longer) galvanised ring shank nail should be used at 200mm centres, which equates to 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 lead to internal damage to the ceiling. All nails must be non-rusting (galvanised).


Fixing steel is easily achieved with the use of self-drilling/self-tapping screws of the appropriate length. Strawboard If the ‘Strawboard’ or ‘Stramit’ is in good condition (ie dry and intact) and you wish to fix through it into the joist, a 125mm screw at 200mm centres along each joist is sufficient. The ‘Strawboard’ or ‘Stramit’ may have been fitted into a steel profile support. It is possible to use a self-drilling/ self-tapping screw into the steel for fixing the decking board.