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How to build a raised deck
Create an elevated terrace with decking
A raised deck is a great way to make the most of space that can otherwise go unused, such as slopes and uneven areas. Create a level space for entertaining, eating al fresco, or just sitting out and enjoying the sunshine.
Before you start, head to our guide to planning your decking project for an essential introduction. This covers everything from how many boards you'll need to what design you should arrange them in.
Our example is of a deck that is:
- Raised - not laid on the ground floor
- Built on flat, soft and level ground
- Attached to a building (or wall) - ignore this section if building independently from a building
- Designed with the boards in a horizontal pattern
- Fitted with a balustrade made from spindles (balusters)
- Fitted with decking steps (with options for both timber and solid composite decking) and accompanying handrail
- Finished with skirting panels
If you plan to lay a more simple deck on the ground floor, check out our article on laying a basic deck for more information.
Let's start with constructing your elevated deck.
- 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.
This list includes everything you will need to build a raised deck. Some of the items are necessary for more than one stage of the project, so do check the steps thoroughly for the tools and equipment needed.
You might need:
To prepare and square the site
- Tape measure
- Builder’s line
- Club hammer - to hammer in the pins
- Edger - also known as a half moon lawn edger or edging iron
- Spirit level - we recommend using one over 450mm in length
- Weed control fabric and pegs - to prevent weed growth, but still allow rainwater to drain through
- Builder’s square
- Line level
- Masking tape
To attach a deck to a building
- Stainless steel washers
- Combi drill
- Flat wood drill bit
- Anchor bolts - also known as expansion bolts
- 22 x 100mm (approx.) lengths of timber - for profiles
- 22 x 50 x 1800mm (approx.) length of timber - to make the builder’s square
- 90 x 90mm joist support posts
To build the sub-frame and cut deck boards
- Quick-drying concrete - if required
- Brick trowel - if making concrete pads
- Aerated blocks
- Metal joist hanger
- 50mm nails
- Decking joists
- Coach screws - 8 or 10mm x length required dependent on what you're securing together
- Coach bolts - 8 or 10mm x length required for joining joists together, if needed
- Socket set - for the coach screws
- Panel saw - for a small project or cutting a few very thick pieces of timber, if necessary. Finer-toothed saws offer a neater finish, but take longer to cut with.
- Jigsaw - for making fiddly cuts in timber, if necessary
- Mitre saw - ideal for larger projects
- Circular saw - for cutting lots of thick timber, if necessary
- Sandpaper or sander
- Decking end grain protector
- Paint brush - to apply the end grain protector
To lay deck boards
- Decking boards
- Decking screws - we recommend choosing screws that are at least 2.5 times longer than the surface they'll be secured to (the deck boards). And if laying Grassedeck boards, opt for green-coated decking screws to minimise the appearance of the screw heads.
- Twist bits
- Hand plane or electric planer - if necessary
To add a balustrade
- Quick-release clamps
- Decking posts
- Decking hand rail
- Decking base rail
- Balustrade screen or spindles
- 12mm wooden dowels, cut to 75mm long
- Exterior wood adhesive
To add decking steps
- Paving slabs or block paving - for a secure footing
- Decking step risers
- Decking step timber treads
- Claw hammer
- Coach screws - 6 or 8mm in diameter, with the length dependent on what's being secured
- Reciprocating saw - if necessary
To fit solid composite stair treads
- Solid composite deck boards - includes start clips and fasteners when purchased online
- Start clips and hidden fasteners set - only needed as separate purchase if solid composite deck boards are bought in-store
- Solid composite decking screws
- HSS 3.5mm diameter drill bit
To add skirting panels
- Lattice panel
- Panel frame - if required
- Wire mesh - if required
- Wire cutters - if required
- 30mm exterior screws
- 20mm wood staples
- Protective gloves - if mixing concrete
- Rigger gloves - for handling the timber
- Safety goggles
- Dust mask - look for ones that are suitable when cutting timber
- Ear plugs - when using power tools. Check they work with other safety wear. As for instance, ear defenders worn over goggles may create a gap which lets the sound in - therefore we recommend ear plugs.
- Knee pads
- Decorator gloves - for applying the end grain protector
Before you build the deck, the site needs to be prepared.
Measure out the site according to your plan and hammer a peg into each of the four corners.
Run a builder’s line from each of the four pegs. This will help you visualise the site.
Clear away all vegetation and rocks within this marked site.
If clearing turf, use an edger to cut into the lawn (it provides a clean, straight cut) and remove the grass with a spade.
Lift the turf in manageable strips, and save it somewhere out of the way (it could be used around your completed deck later on).
Once the site area has been prepared, it's essential to ensure that the sides of the deck are completely square. This is key as the decking will be laid with joist support posts concreted into position. Once these are installed there's no way to move them if they've been put in the wrong place. It will also ensure that your finished deck will look professional. So a bit of extra time spent now on checking the site can help prevent any unwanted problems later on.
The easiest way to achieve this is by using the 3-4-5 triangle method.
The 3-4-5 triangle explained
The 3-4-5 triangle method uses simple geometry to create perfect right angles at the corners. For example, 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.
In our steps below, we will measure 900mm - 1200mm - 1500mm (or you could measure 3ft - 4ft - 5ft).
Make timber profiles to help you set out the deck sub-frame accurately. Cut three 600mm lengths of 22mm x 100mm timber for each profile.
Cut two of the three pieces to a point at one end as these form stakes that will be driven into the ground.
Nail the third piece - the crosspiece - to the top ends of the stakes, attaching the three together to form a profile. Place the nails roughly 50mm from the top of the stakes.
Take up the pegs and lines.
Hammer two profiles into the ground at each corner of the site, about 450mm beyond the cleared area. The centre of each crosspiece should be parallel with the perimeter of the cleared area.
Run a builder’s line from each profile to its opposite and tie it taut, checking that it's perfectly horizontal and not angled.
Hang a line level from the middle of the taut string and hammer the profiles in until you get a level reading. Use a spirit level to ensure that each crossbeam is also level.
Check that the lines are crossing directly at the corners by laying a joist along the edge of the cleared area - this represents 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.
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.
If the measurement is less than 1500mm, the angle's too small and needs to be opened up a bit. If it's more than 1500mm, the angle's too big and needs to be closed. Make any necessary adjustments by sliding the string along the profiles and checking.
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 small saw cut at the pencil mark. Then tie the line firmly in position at the cut.
Top tip: Corner to corner
As a final check, measure the diagonal distances from corner to corner. If they are the same, then each corner will be a right angle.
This stage involves fixing one joist directly to the wall. You can skip this section if your decking is not being fixed to a wall. The rest of the decking's sub-frame is then aligned with it.
Before starting, check that you won't be blocking off any air bricks or interfering with the damp-proof course (DPC) by attaching the joist.
Drill holes at 400mm intervals along the length of the joist being fixed to the wall. Arrange the holes alternately at the top and bottom. Make sure that they are not too close to the edges, or else they will weaken the joist. Check that they don't coincide with the eventual positions of the joist hangers. Measure and plan the position of the holes so that the bolts are secured into the brickwork and not the mortar.
Use a flat wood bit to drill recesses in the joist - just deep enough for the nuts and wide enough to allow access for a socket spanner. Make sure you’ve measured and drilled accurately or else the bolts won’t work.
Position the joist on the wall using a spirit level to ensure it's level. Make a mark on the wall through each hole.
Remove the joist and select ‘hammer action’ on your drill to drill through the masonry at the marked points. If you've measured correctly in Step 1, drill into the brick - not the mortar.
There must be a gap between the timber and the wall to allow rainwater to run down the wall and not pool on the decking.
To create this gap, make a spacer from a few stainless steel washers - they should measure a minimum of 10mm when fitted together.
Place the spacer between the joist and the wall and secure the joist to the wall by inserting expanding masonry bolts into each of the holes. Tighten the bolts with a socket spanner - taking care not to over tighten.
As well as posts at the four corners (corner posts), an elevated deck is also raised on joist support posts. The corner posts don’t sit right in the corners of the sub-frame. They are offset by the width of a post to allow deck posts (which will be needed when attaching railings or balustrades) to be slotted in later. A lot of the work at this stage requires two pairs of hands.
In the corners of the marked area, dig out 700mm deep holes 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 should be a maximum of 1.8m in any given direction - we recommend 1.5m. The corner posts should not be right in the corners but offset to one side by the width of a post. It doesn't matter which side as long as they're level down each length and flush ready for the outer joists to be fixed later.
Top tip: Bring in a block
For extra stability, place half an aerated block at the base of the hole. Place the post in the hole on top of the block, checking it’s straight using a spirit level.
Create wooden props to hold the joist support posts in place.
Use pieces of timber, we suggest 19mm x 38mm or similar for a good size. Screw the pieces together to form an L or T shape. Use a panel saw to spike one end of the prop to help secure it into the ground.
Screw the props to the joist support posts and use a spirit level to keep checking that the joist support posts are vertical.
Pour quick-drying concrete into the holes and slope the concrete away from the posts.
When all the posts are in place and the concrete is set or hardened off, remove the lines, profiles and wooden props.
Fit a sheet of weed-control fabric around the posts and cover it with gravel.
Allow the concrete to set (as recommended by the instructions) before building the sub-frame.
The sub-frame forms the deck’s outer skeleton. Joists run in the opposite direction to the deck boards, so it's important to have settled on a decking design. For more on the different deck board arrangements, head back to our planning article.
And don't worry if there are any existing features (such as trees or posts) that you can't, or don't want to remove - just work around them. Include a bit more sub-structure to frame the obstacle and support the deck boards. Block off the area around it by positioning joist off-cuts between the inner joists (secured either end with two coach screws). Then simply cut and fix the deck boards to fit around it.
If it is a tree, leave enough space for its trunk to thicken and for it to sway in the wind. And be sure to swot up on what species it is, as some can be very fast growing.
Cut the outer joists of the sub-frame to length, remembering to allow for overlapping corner joints.
Coat the cut ends with an end grain preserver using a brush.
Attach the sub-frame joists to the wall joist with metal joist hangers and 50mm galvanised nails. To avoid splitting, pre-drill the holes for the galvanised nails.
If you're not fixing to a wall, fix the joists to all the corner posts as per the following steps.
Fix the side joists to the off-set corner posts, first checking that they are level. They need to protrude by the width of a deck post to allow for a balustrade (or railing posts) to be fixed into place within the frame.
Drill holes through the joist into the post and countersink the heads using a flat wood drill bit to create the recess to house the screw heads. Attach with two coach screws using a socket set with ratchet handle.
Recess and drive in two more coach screws at the corner to join the outer joists together (as shown).
Continue round the deck fixing the joists to each post with two countersunk coach screws.
To give extra strength to the sub-frame, 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 to the joist sub-frame with two countersunk coach screws at either end, or to the wall joist using joist hangers.
If you're laying timber deck boards in a horizontal pattern, the distance between the centre of one joist and the centre of the next should be a maximum of 450mm. For diagonally laid timber boards, the centres should measure 300mm.
Top tip: Bowed joists
If you find that any of your joists bow slightly, fix them with the bow projecting upwards. Even if you don’t notice an obvious bowing, check the joists are level with the sub-frame using a straightedge. If necessary plane any excess to ensure the deck boards will lie flat.
It's important to attach balustrades (or railings) to a deck after you've built the sub-frame, but before you lay the deck boards. This is because the decking posts slot in and are fixed to the corner posts, and then the deck boards fit around them.
We're going to run through attaching:
- decking posts
- a handrail
- a base rail
- and wooden spindles (also known as balusters)
But there are plenty of other options. Instead of spindles, opt for a balustrade screen. Finish your decking posts with post caps or ball tops. Add a gate to keep young children and pets safe in one place. Or keep things simple with a complete railings kit. For more on these, and other, decking accessories, check out our decking buyer's guide.
Work out how high you would like the balustrade to be. Cut the wooden spindles down to size if necessary, bearing in mind all safety considerations and Building Regulation requirements.
And don’t forget to allow space beneath the base rail for the deck boards.
Decide how to space the deck posts (we recommend a maximum of 1.2m apart) and cut the base and hand rails exactly to length.
Clamp a length of base rail in a workbench and drill pilot holes 100mm apart all the way through the rail.
Slot the spindles into the underside of the hand rail and secure them by screwing diagonally through the spindle into the rail.
For accuracy, measure the intervals using a spacer made from a wood off-cut, as shown.
Remember the slotted sides of both the rails are fitted facing downwards so that rainwater cannot collect in them.
Fit the base rail onto the spindles and screw 50mm deck screws through pilot holes into the bottom of each.
Use the wooden spacer again to align the spindles precisely.
Slot a deck post in the gap between the joist support post and the corner of the sub-frame and hold it in place with a quick-release clamp.
Fix the post to the sub-frame with two coach screws countersunk.
Make the corner post more secure by fitting a piece of joist off-cut between the corner post and the first inner joist. Screw to the sub-frame with deck screws.
Position the next deck post and fix it with just one coach screw for now, so that you can push it to one side while you fix the balustrade.
Mark a 12mm drill bit with masking tape at 38mm from the tip. Then drill two holes to that depth on either end of both the hand and base rails.
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 balustrade assembly into place.
Use quick-release clamps to hold the posts and balustrade together while the glue dries.
Then add another coach screw to the base of the second post to secure it.
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.
For help on cutting deck boards, head to the 'How to cut deck boards' section of our article 'How to build a basic, ground-level deck'.
Lay boards at the outer edge of the sub-frame and move inwards.
Cut notches in the first board to fit around the deck posts. To do this, cut the board to length and clamp it in position in front of the deck posts, overhanging the sub-frame.
Measure and mark the outline of the deck posts accurately onto the deck board with a combination square or builder's square.
Remove the deck board and clamp it firmly to a workbench.
Cut out the shape of the deck posts using a jigsaw - and not forgetting to treat the cut edges with an end grain protector.
Slot the cut deck board into position. If necessary, plane or saw down its outer length to ensure that the inner edge is flush with the inside edge of the deck post. This will give you a straight edge from which to lay the rest of your deck boards.
To lay the rest of your deck head to our 'How to build a basic, ground-level deck' article. The section titled 'How to lay timber deck boards' provides step-by-step help for timber boards. Whereas for solid composite boards, read the section 'How to fit solid composite deck boards'.
A basic open stair is all that’s necessary on a low deck, but for higher ones you’ll need handrails. Be sure to check the most up-to-date Building Regulations.
The easiest way to build steps is to buy pre-formed kits that include two stair risers (side panels) and step treads. They're available in three, four and six step options.
Alternatively, build your own with two risers (side panels) and as many separate step treads as you require. We're going to take you through this process for timber deck boards. If looking to lay solid composite decking steps, follow steps one and two below and then jump to the section 'How to fit solid composite stair treads'.
If building your own steps, we suggest:
- A step tread width (the width of the steps) of 900mm - it should not be less than 760mm.
- Stairs wider than 900mm will need to add a central step riser to support the steps and prevent them buckling.
- A step depth (the vertical distance between each step) of between 150 and 180mm if building your own riser. This ensures the steps are a comfortable depth and not so deep that they're an effort to climb, but not so shallow that you trip on them. This is especially important for the bottom step - between the step support pad (the step's foundation) and the first riser.
Top tip: Layered timber decking
Consider using a layered surface deck board, such as the Walksure or Grassedeck deck boards, for your steps. The extra layer improves the grip, making it a safer step.
Check that the site for your steps is level and firm - anything uneven or too soft and the steps won't be secure enough and might sink into soft ground.
If no hard landscaping exists there already, consider laying an area of concrete or paving slabs (British Standard Paving is a very strong and durable option). For more on paving options, head to our buyer's guide.
Cut two sections of joist off-cut to the same width as the step treads.
Attach them to the step risers at the top and bottom using two countersunk coach screws on each side.
Position the assembled steps against the sub-frame of the deck and in the centre of the step support pad.
Ensure you have the longest edge of the stair riser on the paving slab and the short edge against the deck.
Drill pilot holes through the step assembly and the sub-frame joist. Screw the step assembly securely to the sub-frame with four more countersunk coach screws.
Drill pilot holes and then screw the treads into the riser supports at either end with two 50mm deck screws to make a sturdy step.
To fit solid composite stair treads, see 'How to fit solid composite stair treads'.
If you would prefer a solid stairway to an open stair, fill the gaps with joist off-cuts or deck boards.
Simply measure the height and depth of the gap and screw the timber into the step riser with two screws at either end.
Solid composite deck boards are narrower than timber deck treads, and so two are required to be fitted width to width to provide a comfortably deep stair tread.
Follow steps one and two of 'How to add decking steps' before starting step one below.
Install start clips against each riser of the first step.
Position the solid composite deck board into the start clips and fix the universal fasteners to the front of the deck boards creating the 6mm expansion gap for the second board.
Position the second board and secure with 63mm solid composite deck screws from the top of the second board into the risers.
Repeat this process for each of the steps.
In order to fit handrails to your steps, you’ll first need to fix notched deck posts at the top and bottom. Notched (or rebated) deck posts have had a section of the post removed in order that it butts up to the steps better.
Measure and mark the post accurately with a square prior to making any cuts.
Use a reciprocating saw or jigsaw to score the post. Remove the weakened sections with a chisel making sure not to remove more than half the post or you’ll significantly weaken its structural integrity.
Smooth down any rough or cut edges with sandpaper and treat with an end grain protector.
Drive two coach bolts through each post into the step riser.
Position a length of hand rail on the outside face of the posts parallel with the angle of the steps.
Mark with a pencil the line of the outer edges of the posts and cut along this line with a jigsaw.
Bolt the hand rail to the posts and check that the edges are neatly flush.
To attach spindles, fit a base rail in the same way as the hand rail. Then cut the spindles to length and screw them in place.
You can add decorative skirting to the exposed space beneath a raised deck by fitting lattice panels.
This can be a practical feature as well, hiding away anything you wish to store beneath your decking and preventing small children and pets from wandering underneath. We're also attaching a wire mesh behind the lattice in our step-by-step advice below, as this helps prevent garden debris and animals from getting under the deck.
If you need access, consider hinging or a different fixing to be able to easily remove the panels.
Measure from the bottom of your sub-frame to the ground.
Cut the lattice panel to fit these measurements with a jigsaw.
If your lattice panel has a frame, 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 to the cut edge of the lattice.
Measure the lattice panel (within the frame) and cut a section of fine wire mesh with wire cutters to fit.
Attach the wire mesh to the batten frame or directly to the lattice panel with wood staples and a hammer.
Drill pilot holes and screw the upper frame of the panel into the deck sub-frame using 65mm deck screws. A pilot hole will help prevent the frame from splitting.