How to lay new decking boards

Use this installation technique to finish a new deck or to replace old boards on an existing base

How to lay new decking boards

Once a decking framework is complete it's time to clad it with timber decking boards. Decking is secured to the top of the joists, positioned to run across them and parallel to the beams.

Timber boards are available in a range of species including merbau, spotted gum and treated pine, and come in three basic sizes from large 140mm wide boards, to medium-sized 90mm and narrow 70mm boards.

The exact sizing varies with the different timber species and composite boards are also available in 88 and 137mm widths.

Boards may be flat on both sides or ribbed on one side. Laying boards ribbed side up or down is a personal choice, but we prefer ribbed side down to reduce surface contact between joist and decking. This also helps trapped water to evaporate and reduces the risk of subsequent decay.

Boards should be laid straight and positioned with 3mm spaces in between using either specialty spacing tools, nails or wedges to ensure the gaps are even.

Choosing the fasteners

Decking boards are best secured using galvanised or stainless steel twist nails. Keep the nails 12mm from the board edges and secure them flush with the surface.

Alternatively use galvanised, stainless steel or treated pine decking screws. To save time and avoid drilling a pilot hole for each screw, use self-drilling stainless steel or treated pine decking screws.

Specialty products are also available to edge-fasten boards for a clean surface look.

Position and cut the boards

Step 1. Position and cut the boards
Lay five rows at a time with 50mm overhang at each end, overlapping the joints at the nearest joist. Use a combination square to mark a line on the boards showing the joist positions then cut to length with a mitresaw.

Mark the joist centrelines

Step 2. Mark the joist centrelines
Check the board joints are square and centred over the joists then position a straightedge or spirit level across the boards at the centre of each joist to mark a line.

Mark the screw positions

Step 3. Mark the screw positions
Use a 40mm square offcut as a spacer to mark across the line to show drilling points. Make narrow wedges 100mm long using a mitresaw then tap them between the boards at every second joist to keep the gaps even.

Secure the screws

Step 4. Secure the screws
Use a drill and 2mm combination countersink bit to make pilot holes at the marks, drilling only through the board if the joists are treated pine. Use a square drive bit to secure screws, adjusting the torque clutch as needed.

Check the alignment

Step 5. Check the alignment
Position a stringline along the complete length of a row, every five rows to check the boards are straight, adjusting if needed and using a chisel to prise the gaps slightly further open or closed as required for even spacing.

Trim the board ends

Step 6. Trim the board ends
Mark a cut line on the end of the boards, leaving a 20mm overhang, cut using a circular saw and round over with 120 grit abrasive paper. TIP Use a handsaw to cut the last board where the circular saw won't reach.

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