An elevated deck is a great way to use sloping or uneven land, gives you an attractive and versatile addition to your property and is a great focal point for entertaining and spending hours in the garden.
Tools & materials required
- Always wear safety goggles and a dust mask.
- Ensure that you check for service cables before metal post supports are used, or digging holes.
- Wear protective goggles and a mask when spraying wood preservative.
- Get a helper to assist you, especially for lifting large panels.
- Wear strong gloves to protect your hands from splinters.
- Ensure young children are not able to play underneath your new decking.
Preparing your site
Start by clearing away all the vegetation, rocks and trees that don't feature in your deck design, taking care not to disturb any drains or underground cabling. If the site is on a lawn, take up the turf and make sure you have enough drainage.
Then, in accordance with your deck plan, measure out the site and hammer in four wooden pegs at each of the corners. Run a builder's line from each of these to help you visualise the site. After that, lift the turf in manageable strips with a spade - saving some for making good around the site later. Finally, level off the earth if the site isn't quite flat.
How to attach a deck to a building
If you want to join your deck to your house, be careful not to block off any air bricks or interfere with the damp-proof course.
Top tip - Elevated decking on concrete
If part of your elevated deck extends over concrete, you don't have to take the concrete up. Instead, position the posts in metal post supports, screwed down with expanding masonry bolts. Use chalk instead of pegs when you mark out the site and when squaring it drive in the wooden profiles beyond the concrete (even if this is some distance from the site).
Fix one joist directly to the masonry and then set out the rest of the sub-frame in line with it. Drill holes at 400mm intervals along the length of this joist. Arrange the holes alternately at the top and bottom so as not to weaken the joist and make sure they don't coincide with the eventual positions of the joist hangers.
Check the joist is level and make a mark on the wall through each hole. Then remove the board and drill through the masonry at the marked points. Place the board back in position, insert expanding masonry bolts into each of the holes (remembering to include the washers) and tighten them with a spanner.
How to square your site to build an elevated deck
Take your time to measure everything carefully at this stage - it'll be well worth it in the long run. Use the 3-4-5 triangle method to make sure your corners are accurate and that your finished deck looks professional (see 'How to make sure your elevated deck is square' section).
Top tip - Corner to corner
As a final check, measure the diagonal distances from corner to corner. If they're the same, each corner will be a right-angle.
Make timber profiles to help you set out your deck sub-frame accurately. Then cut three 600mm lengths of 25mm x 100mm timber for each profile. Two of these will form stakes that you'll drive into the ground, while the third will be a crosspiece. Cut the stakes to a point at one end and nail the crosspiece 50mm from the top.
Take up the pegs and lines and hammer two profiles into the ground at each corner about 450mm beyond the cleared area. Next, run a builder's line from each profile to its opposite and tie it taut. Place a line level in the middle and hammer in the profiles until you get a level reading. Use a spirit level to make sure each crossbeam is level.
Check the lines cross directly at the corners by laying a joist along the edge of the cleared area to represent the edge of the sub-frame. Then stand a spirit level vertically against it at the corner. Adjust the position of the lines on the profiles until they cross directly above the corner of the cleared deck area.
Use the 3-4-5 triangle method to square the corners, making any adjustments by sliding the string along the profiles. When the lines are perfectly level and square, mark the position of the string on each crosspiece with a pencil. Move it to one side and make a saw cut or hammer in a nail at the pencil mark. Then tie the line firmly in position.
How to make sure your elevated deck is square
It's vital at this stage of the project that the sides of the deck are square to each other. The easiest way to do this is by using the 3-4-5 triangle method, which uses simple geometry to create perfect right-angles at the corners.
In a triangle with sides exactly 3, 4 and 5 metres long, a right angle will form at the corner where the shorter sides meet. Any multiples of 3, 4 and 5 will follow the same pattern. So first, use a spirit level or plumb line to ensure the lines between the profiles cross directly above the four corners of your site. Then either use a wooden builder's square or measure and stick masking tape 900mm from the corner on one line and 1200mm from the corner on the other.
When the diagonal distance between these two marks measures exactly 1500mm, the corner is a true right-angle. Make any necessary adjustments by sliding the string along the profiles.
How to fix joist support posts for an elevated deck
An elevated deck is raised on joist support posts. The corner posts don't sit right in the corners of the sub-frame, but are offset by the width of a post to allow deck posts to be slotted in later. You'll find that a lot of the work at this stage really needs two pairs of hands, so it's well worth asking someone to help you.
Dig holes 600mm deep for each of the joist support posts. Ideally, the holes need to be about 300mm in diameter at the top and 400mm at the bottom. The gap between the centre of one post and the centre of the next must be a maximum of 1.2m. The corner posts shouldn't be right in the corners, but offset to one side (it doesn't matter which) by the width of a post.
Put the post in the hole, and check it's vertical by using a spirit level. Hold the post in position with temporary supports and pour quick-drying concrete into the hole.
When all the posts are in place and the concrete is firm, remove the lines and profiles.
Fit a sheet of weed-control fabric around the posts and cover it with gravel. This will stop weeds from growing through and let water drain away too. Leave the concrete to set for 48 hours before you build your sub-frame.
How to build a joist sub-frame for an elevated deck
The sub-frame forms the deck's outer skeleton. Remember that joists run in the opposite direction to the deck boards, so you'll need to decide early on which way you want the deck boards to run.
Top tip - Joist hangers
Galvanised metal joist hangers will help you fix the sub-frame joists quickly and securely to a wall joist.
Cut the outer joists of the sub-frame to length (remembering to allow for overlapping corner joints) and paint the cut ends with end-grain preserver. Then attach the sub-frame joists to the wall joist with metal joist hangers and 50mm galvanised nails.
Top tip - Bowed joists
If you find that any of your joists bow, fix them with the bow projecting upwards. Even if you don't notice an obvious bowing, it's worth checking the joists are level with the sub-frame using a straightedge. And if you need to, plane any excess to ensure your deck boards lie flat.
After checking they're level, fix the side joists to the off-set corner posts. They need to stick out by the width of a deck post. Drill holes through the joist into the post and attach with two countersunk coach screws. Then drive in two more coach screws at the corner to join the outer joists together.
Carry on fixing the joists to each post with two countersunk coach screws.
To give extra strength to the subframe, you should screw two support beams onto every second post along the length of the deck. Position them immediately beneath the joists of the sub-frame.
Cut the inner joists to length and attach them to the joist sub-frame with two countersunk coach screws at either end, or to the wall joist using joist hangers. If you're planning to lay your deck boards in a horizontal pattern, the distance between the centre of one joist and the next should be 400mm. Or, for diagonally-laid boards, it should be 300mm.
How to fit a balustrade for an elevated deck
You'll need to attach the railings to a deck after you've built the sub-frame, but before you lay the deck boards. Work out how high you'd like the railings to be, and cut the balusters down to size if you need to. Bear in mind that for safety reasons, the handrail must be between 900mm and 1m above the finished deck, and the base rail a maximum of 75mm. Don't forget to allow space beneath the baserail for the deck boards.
Decide how you're going to space the deck posts (remember they should be a maximum of 1.2m apart) and cut the base and handrails exactly to length. Clamp a length of baserail in a workbench and drill pilot holes 100mm apart (or less, if you want your balusters more closely spaced) all the way through the rail.
Slot the balusters into the underside of the handrail and secure them by screwing diagonally through the baluster into the rail. For accuracy, measure the intervals using a spacer made from a wood off-cut, as shown. Remember that the slotted sides of both the rails need to be fitted facing downwards, so rainwater can't collect in them.
Fit the baserail onto the balusters, and screw 50mm deck screws or galvanised screws through the pilot holes into the bottom of each. Use the wooden spacer again to line up the balusters precisely.
Slot a deck post in the gap between the joist support post and the corner of the sub-frame, then hold it in place with a quick-release clamp. Fix the post to the sub-frame with two countersunk coach screws.
To make the corner post more secure, you can fit a piece of joist off-cut between it and the first inner joist, screwed to the sub-frame with deck screws. Then position the next deck post and fix it with just one coach screw for now, so you can push it to one side while you fix the railings.
Mark a 12mm drill bit with masking tape at 38mm from the tip, and drill two holes to that depth on either end of both the handrails and baserails. Fit 12mm wooden dowels into the holes, and mark the corresponding positions on the adjoining posts at top and bottom. Then drill 38mm holes in each post at the four marked points.
Glue the wooden dowels into the holes and slot the railing assembly into place. It's good to use quick-release clamps to hold the posts and railings together while the glue dries. Then add another coach screw to the base of the second post to secure it.
How to lay boards for an elevated deck
When the railings are in place, you're ready to lay your deck boards. Remember that they need to run in the opposite direction to the joists.
Make sure children can't play underneath your elevated deck and become trapped.
Start by laying boards at the outer edge of the sub-frame and work your way inwards. You'll have to cut notches in the first board to fit around the deck posts. Cut the board to length and clamp it in position in front of the deck posts, overhanging the sub-frame. Then measure and mark the outline of the deck posts accurately on the deck board.
Remove the deck board and clamp it firmly to a workbench. Cut out the shape of the deck posts using a jigsaw.
Slot your cut deck board into place. If you need to, plane or saw down its outer length to make sure the inner edge is in line with the inside edge of the deck post. This'll give you a straight edge from where you can lay the rest of your deck boards. Screw the board down into each joist using 50mm or 63mm deck screws or galvanised screws (depending on the thickness of your deck boards).
Fix each deck board with two screws into each joist before you move onto the next, remembering to leave a 3mm gap between the boards. You'll need to position your joins exactly half-way across a joist - that way you can screw both boards into it. You'll also need to stagger the joins and to get a professional effect you can arrange them into a regular pattern across the deck surface.
How to fit skirting panels for an elevated deck
On a raised deck, you can cut lattice panels to fit beneath the sub-frame and this will create an attractive skirting. By attaching a wire mesh behind the lattice, you can stop bits of garden debris and small animals from getting under the deck.
Measure from the bottom of your sub-frame to the ground. Then with a jigsaw, cut the latticed panel to fit these measurements. Remove the frame batten from the discarded section by gently knocking it away from the lattice with a hammer. Then use 30mm galvanised screws to fix it back into place on the lattice you want to fit.
Measure the lattice panel (within the frame) and cut a section of fine wire mesh with wire cutters to fit. Then fix the wire mesh to the batten frame with wood staples and a hammer.
Finish by drilling pilot holes and screwing the upper frame of the panel into the deck sub-frame.
Adding a gate
If you have small children or pets, a gate will make your deck a safer place. It's best to use a lightweight gate that can hang from a deck post.
If you opt for a ready-made gate you'll need to source and measure it before drawing up your plans, so you can position the deck posts and steps to fit it. Alternatively, you can make a gate yourself or have one made to fit the gap. If you choose a metal gate, it'll usually come with a hinge assembly and automatic latch.
Working around existing features
Instead of cutting down a tree, why not build your deck around it? All you need do is include a bit more sub-structure to frame the trunk.
Simply block off the area around the tree by putting joist off-cuts between the inner joists, and secure them at either end with two coach screws. Remember to leave enough space for the tree trunk to thicken and sway in the wind. Then cut and fix the deck boards to fit around the tree.
Protecting your deck
To keep your deck looking its best, you can protect it from the elements and everyday use with a regular coat of stain, oil or seal.
You can get deck stain in hardwood tones as well as more unusual colours which will be water-resistant and hard-wearing. Deck oil will protect and enhance the natural beauty of your wood, while colourless deck seal locks out moisture while allowing the timbers to breathe and weather naturally.
You can also revive older decking with specially formulated deck cleaner, which removes mildew and dirt and visibly refreshes faded timbers.