Building a timber deck

The steps, in order

1. Settle the supports before anything else

   Over a sound slab or an existing patio, adjustable pedestals do the job and take up the fall. On open ground it is concrete pads or ground screws, spread as the board maker requires. While you are at it, check the finished height against the door threshold and which way water runs off: neither is easy to correct later.

   Tools: tape measure, laser level, string line

2. Prepare the ground and stop the weeds

   A shallow dig out, a weed membrane and a compacted layer of gravel beat a weedkiller that lasts one season. Water has to get away and air has to move under the finished deck: a deck boxed in on every side dries badly and the timber pays for it.

   Tools: spade, rake, wheelbarrow, plate compactor

3. Set out and level the supports

   String lines pulled tight, squareness checked on the diagonals, levels transferred with the laser, and the fall the manufacturer asks for. Every pedestal is set to its final height now: a support packed out later with an offcut is the one that will creak.

   Tools: rotary laser, string line, square, mixer

4. Fix the joists

   Joists run at right angles to the boards, at the spacing the maker gives for the board thickness you bought. They never touch soil, and a protective strip separates them from the supports. Leave the expansion gaps specified at the ends and against walls: timber moves with the weather, all year round. The decking calculator counts joists, boards and screws from that spacing.

   Tools: circular saw, drill driver, spirit level, SDS-Plus rotary hammer

5. Screw down the deck boards

   The gap between boards is in the instructions, because it depends on the species and on the moisture content of the timber on the day: boards delivered wet will shrink. Pilot drill near the ends so nothing splits, use stainless fixings in the grade recommended, and line the first board to a string: everything else follows from it.

   Tools: impact driver, spacing jig, clamps, pilot drill bit

6. Cut the edges and finish the ends

   Rather than trimming each board, lay them long, then cut the whole edge in one pass with the circular saw run against a guide. A fascia board closes the ends, a step takes up the height, and any ventilation openings are left clear.

   Tools: circular saw, guide rail, mitre saw

7. Protect it, then look after it

   Every species silvers in the sun, and that is looks, not disease. A decking oil slows it down and needs redoing. For cleaning, a stiff brush and water usually do; keep the pressure washer well back and on a low setting, or it will carve out the soft grain and leave the deck furry.

   Tools: stiff brush, decking oil, pressure washer

Consumables

• Deck boards, timber or composite, in a use class that suits where they are going.
• Joists compatible with the boards and with the way they are fixed.
• Adjustable pedestals over an existing surface, or concrete pads and ground screws on open ground.
• Weed membrane and gravel for compacting.
• Stainless fixings in the grade the supplier recommends, or hidden clip fasteners.
• Protective strips between joists and supports.
• Fascia board to close the ends.
• Decking oil, if you want to hold off the silvering.

Safety on this job

• Circular saw: goggles, work clamped down, no hand in line with the blade, and a stable footing for the edge cut.
• Wood dust: a mask when cutting, especially with tropical hardwoods and composites, some of which irritate.
• Splinters and treated timber: gloves for handling, and wash your hands before you eat.
• Handling: a pack of boards takes two people, and it is stored flat, on bearers, out of driving rain.
• Buried services: before digging for supports, find out where the water, gas and electricity run.