How to build decking
A garden deck is a perfect starting point if you're new to carpentry. In this guide, we show you how you can build your own decking at ground level. If you want to build a raised deck, take a look at our how to build a raised deck guide.
Steps:
Decking essentials
- We recommend undertaking any decking project with the help and assistance of a friend.
- Always wear protective safety gear when necessary.
- If securing your decking with footings, make sure there are no cables or pipes underneath where you want to dig. Rent a cable avoidance tool (CAT) to conduct these checks and if found, we suggest reconsidering your decking plans. Or consider installing a hinged trap door in your decking to allow future access to the area.
- Don't burn the off-cuts of pre-treated timber decking as the smoke and ash produced is toxic. Dispose of them as you would ordinary household waste.
Protective kit
- Protective gloves - for mixing the cement, if required
- Rigger gloves - for handling the boards
- Safety goggles
- Dust mask - look for ones that are suitable for cutting timber
- Ear plugs - when using power tools. Check they work with other safety wear. For example, ear defenders worn over goggles may create a gap, which will let the sound in, so we recommend ear plugs.
- Knee pads
- Decorator gloves - for applying the end grain protector
Clear away any plants, rocks or weeds. Use an edger to cut into the lawn for a straight cut, and then use a spade to remove the turf.
Use a straightedge (a deck board is perfect for this) with a spirit level on top to check that the whole area is level, and level out any slight unevenness in the ground.
Choose what surface your decking is going to be laid on. There are two options when building on soft ground:
-
add concrete pads for extra stability
- or lay straight onto the ground for a simple project
We recommend adding concrete pads as they're not only great for stabilising your deck; they'll ensure your decking lasts longer.
If you’re adding concrete pads
It's key that the concrete pads are positioned in the exact places and that they're all square for the deck joists. For help on this, head to the 'How to square a site' section of our How to build a raised deck article for more advice. Work out where exactly the pads are required and dig holes roughly 150mm square and 150mm deep at intervals of 1.2m around the deck. Fill the holes with a quick-drying, ready-to-use concrete to just above ground level. Use a spirit level and straight edge to check that the pads are level with each other, and if not, use a brick trowel to level off the highest points while the concrete is still semi-dry.
When the concrete has hardened off (is completely dry), cover the whole area with weed control fabric (making cut-outs for the concrete pads) and a layer of gravel (40 to 50mm in depth). Cut and lay squares of damp-proof course to sit between the concrete and the deck joists.
If you’re laying straight onto the ground
Cover the area in a layer of weed control fabric and then 40mm to 50mm of gravel.
2. Cut the deck boards
Measure and mark the deck board at the desired length. Use a combination square to mark an accurate line across the deck board. You can cut deck boards using a mitre saw, panel saw or a jigsaw.
Apply a protective treatment to any cut or recessed timber - be it deck boards, joists or posts - before assembling. This is applicable to all timber, including Walksure and Grassedeck boards. There's no need to sand or treat solid composite deck boards
3. Assemble the sub-frame
Before you commit yourself to the build, it’s a good idea to do a dry run of the decking first as you don't want to finish the last row with a thin slither of deck board. Lay out the joist frame and position the deck boards on top, creating the necessary deck board expansion gaps. Timber deck boards require a 5 to 8mm expansion gap along the length of the deck boards and a 3mm gap along the ends of the deck boards.
A gauge screw makes an ideal spacer or use off-cuts of wood. And check that all gaps created are the same for a uniformed finish.
If the deck boards on the end row overhang the joist frame, consider increasing or reducing the expansion gaps of timber deck boards by the recommended amount. Alternatively, shorten or increase the outer frame so that your final decking row will finish flush to the edge of the joist frame. Work all this out before you cut and assemble the deck frame or add concrete pads.
Measure your deck frame and cut to size. Make two pencil marks on each end of the deck frame's two outer joists - these are at right angles to the inner joists. These marks are where the coach screws will go. Make the marks to align with the centre of the adjoining outer joist. This will total eight marks - two in each corner of the outer joist frame. Use a flat wood bit to drill recesses into each of the eight marks. These should be the depth of the screw's head and wide enough for a ratchet or socket attachment to tighten them. Also known as countersunk holes, these recesses ensure the screw heads will be flush with the joist surface for a neat finish.
Replace your drill bit for one that's thinner than your coach screw's shank. Line up the adjoining outer joists and drill a pilot hole through the centre of the recess, from the outer joist into the adjoining outer joist. A pilot hole provides a guide hole to help direct the screws and prevents the screw from splitting the wood.
With the pilot holes drilled, it's now time to fit the coach screws. Use either a drill driver with socket attachment, or socket and ratchet to tighten the coach screws into place. You might find it easier to drill and secure a corner at a time.
Once the outer frame is assembled and in position, it's time to secure the inner joists. Repeat the process to secure two coach screws through the outer frame into each end of all the inner joists. The spacing of your inner joists is dependent on your chosen decking design. For more on this, head to the 'Which decking design?' section of our planning article.
If you're extending your deck further than the length of a joist, clamp the joist sections end to end in a workbench. Place a joist off-cut about 600mm long across the join, and clamp it temporarily to the joists. Secure it with eight coach bolts sunk from the outside of the frame.
When joining lengths of internal joist (which will be hidden by the deck boards), use two 600mm sections of joist off-cut sandwiched either side of the join for a stronger fix.
4. Lay the deck boards
Start in one corner of your sub-frame and position the first board across the inner joists, so that the deck board is in the opposite direction to the inner joists. The board should be positioned flush with the frame. Position any end to end joins between the deck boards halfway across an inner joist so that both boards can be screwed into the joist for extra stability. Mark a cutting line for the end of the first board and cut it to fit. Don’t forget to allow for an expansion gap of 3mm in your measurements when the boards are butted up end to end.
You'll now secure your first deck board to the joists. The deck board has to be secured to every joist it covers over along the sub-frame. Use two decking screws where each board meets a joist.
Mark the screw locations in pencil, ensuring that they're at least 15mm from the end of the board and at least 20mm from the outside edges. There's no need to create recesses or countersunk holes for the deck screws, as they're designed to create their own recess when screwed down for a flush finish. We recommend drilling pilot holes for the screws to help prevent the wood from splitting. Select a drill bit for your drill driver that's thinner than the deck screw's shank and drill pilot holes into the pencil marks - being careful to drill through the deck board and not into the joist.
Screw the decking screws into the pilot holes. If laying grooved deck boards facing upwards, position the screws at the bottom of a groove.
With the first row in place, you can now start the second row - remembering to include the relevant expansion gap between the boards. Stagger the deck board joins across the deck for greater strength, and arrange them in a regular pattern for an attractive finish.
If using Grassedeck boards, lay them facing the same direction for a uniform shade of green. Or switch them around for a contrasting look.
Use sandpaper or a sander to smooth over any cut ends if necessary.
Once smoothed down, use a paintbrush to apply an end grain preserver to protect the timber from rot and decay.
Once the preserver is dry, protect your decking further by applying decking stain, oil or wood paint. For more on caring for your timber decking, check out our how to guide.