Planning & preparation
- This guide outlines the method for installing a raised deck with a timber frame and horizontal deck board positioning. Bear in mind that other decking designs will require different techniques and joist spacing.
- When planning a raised deck, bear in mind that any deck higher than 300mm above ground level will require planning permission.
- Carefully plan your deck before starting, as this will limit cutting and wastage, and will help you to be accurate when ordering the materials you need.
- When deciding where to position the deck, keep in mind factors such as privacy, light, and space. Avoid building in a damp or wet area completely.
- Plan the deck to ensure the fall of the frame is 1:100 and running away from the house; this will aid water run-off and will help to stop the deck from becoming slippery. Bear this in mind when checking the levels throughout the build.
- We would advise that you plan your deck to fit only whole deck boards, to avoid having to cut a deck board lengthways to fill a gap.
- Bear in mind the 5-8mm expansion gaps needed between boards when planning your deck.
- If you are building a deck larger than 3 x 3m, then see our ‘How to Lay a Deck’ video or online guide for information on extending joists and fascias.
- If you are planning to add railings or lighting to your raised deck then you can follow our step by step ‘How to assemble deck railings’ or ‘How to install deck lighting’ guides.
- See our ‘How to build a raised deck’ video for additional help when building your deck.
Do it right
- Always use structural treated timber and screws designed specifically for the job. This will ensure that the deck is built to last.
- Treat all cut surfaces and drill holes with two coats of preservative.
- When sawing, use the 90-degree guide marker on your saw, or a set square, to help you make accurate cuts.
- When drilling, mark out all pilot holes to ensure your fixings are as accurate as possible.
- It’s best to sand any cut ends of timber to prevent splinters from developing.
- It is possible to build a deck on your own, but it is much easier with a spare pair of hands, so ask a friend if they can help out.
- Firmly secure timber and take care when sawing or drilling.
- When drilling, wear safety goggles.
- When using postcrete wear a dust mask, safety goggles and protective gloves and be sure to follow manufacturer’s instructions.
- Wear a dust mask, ear protectors, and safety goggles when using a jigsaw or circular saw.
- Wear a dust mask when sanding any cut ends of wood.
- Wear protective gloves when handling the deck boards or applying wood preserver.
- Always follow manufacturer’s instructions for drying and safety when using wood preserver.
- Offcuts of treated timber should never be burned, but need to be disposed of safely – your local recycling centre should be able to advise.
- You should also bear in mind that joists can be heavy so take care or ask for assistance when moving them.
- Once the decking is complete, add a decking stain to further protect the timber. These come in a variety of colours so be sure to look at the range.
- Treat the wood to preserve timber from damp and to prevent algae growth. How often you should treat the decking will depend on where it is positioned.
- To keep the deck clean, remove any dirt or leaves with regular brushing.
Preparing the area
Measure and mark out the deck area using pegs and string line. Measure diagonally from post to post or use a set square to check the area is square.
Remove the turf and all vegetation from inside the area to a minimum depth of 50mm. Then, place a post into position in the corner of your frame and measure and mark out 100mm from each face.
Remove this soil to a depth of 700mm, being sure to avoid any cables or pipes as you go. You should be left with a 300 x 300mm square hole; this is where the postcrete will be added. Repeat for the other 3 corners.
Split a concrete block in two using a brick bolster. Place a section of block into each of the holes, making sure they are firmly in place.
Place a length of post into the hole, make sure it is longer than you need so you can cut it down later.
Create props by screwing pieces of timber batten to the posts to hold them in place until you are ready to postcrete. Check that the posts are vertical as you go. Repeat for the four corners.
Double check that each post is vertical then secure in place with postcrete. Use a trowel to create a slope in the postcrete so that rainwater runs away from the post on all sides. Follow manufacturer's instructions for setting time. Then, remove the props.
Create a string line around the four corner posts. Find the centre point between posts and hammer a timber batten into place. Repeat this until the five new post markers are in place, but bear in mind that they shouldn’t be spaced further than 1500mm apart.
Dig out around the posts to a depth of 700mm and a width of 300mm, as you did with the corner posts. Then, place a concrete block into the hole, but do not install the posts at this stage.
Assembling the outer frame
If you are on a slope, always measure and work from the corner where the deck will be at its highest above ground level. Mark on the post where the highest part of the frame will be.
Measure from the far side of one post to the far side of the opposite post and cut sections of joist to length. Line up a piece of joist with your mark and temporarily secure it in place with a 64mm deck screw.
To ensure rainwater runs off your deck, factor in a 2mm fall for every metre of decking. So, if your deck is 3m, you should work on a 6mm fall. Bear this in mind when checking the levels throughout the build.
Place your spirit level on top of the frame and lift until it is at the required level, then secure it to the other corner post. You may need a helping hand to hold the frame in place whilst you check the level. Repeat this process until the outer frame is in place.
Mark on the frame where the midpoint of the corner post is. Then, use a set square to draw a straight line downwards. On the line, mark guide holes at 40mm from the top and 40mm from the bottom of the frame.
Use a 40mm flat wood drill bit to make countersunk holes around each of the marks. Then, use a 6mm wood drill bit to drill the pilot holes.
Hang a washer on the end of a 100mm coach screw, insert it into the hole and hand tighten before securing it firmly in place with a 13mm socket set. Repeat this at each end of the four sections of the frame.
Mark on the frame where the centre of the remaining support posts will be positioned and repeat the process of marking and drilling the countersunk holes.
Put a post into the hole in line with your mark on the frame. Check it is vertical then clamp it into place. Secure the frame to the post as before, then repeat until all but the centre post has been put in place.
To add your central support joists, measure from the inside of the frame on one side to the inside of the frame at the opposite side, then cut a length of joist accordingly. Your central joists should run in the same direction that your deck boards will be.
Attach the joist to the post at each end and secure as you did the outer frame. Put the centre post into position, clamp in place and secure as you did the other posts. Make sure the post is vertical before continuing.
Repeat this so the centre post is sandwiched between two sections of the support frame. Once this is done, secure the five new posts with postcrete.
To trim down the posts, rest the set square on top of the outer frame and mark a line on the wood of the exposed faces, and then saw. Repeat this process for all of the posts on your decking.
To prepare your support joists, measure the distance between the central support joist and the outer frame and cut sections to length.
Roll out your landscape fabric and cut to size, making sure it’s as snug to the posts as possible and covering all of the area under the deck. Add gravel and smooth as you go.
Measure 400mm from the centre of the outer frame and mark a line using a set square. This line is the centre of where the first joist will be positioned.
Repeat this at 400mm intervals down the length of the frame. If the final gap exceeds 400mm, add an additional joist, to ensure that the spacing is never greater than 400mm.
Mark pilot holes 40mm from the top and 40mm from the bottom of the outer frame, and drill using a 6mm drill bit.
Secure the joist in your workbench and attach a joist hanger to each end using 30mm exterior screws.
Place the joist into position so that its centre lines up with the 400mm spacer mark.
Make sure the joist is flush with the frame, then secure using 100mm external grade screws and the supplied socket bit. An extra pair of hands, or packers, may be required to hold the joist in place whilst you do this.
To secure the joist to an unexposed side of the frame, drill a skewed pilot hole on either side before skewing the screws into position.
Once the joist is in place, secure the final 30mm screws to the joist hangers. Repeat this until all of the joists are secured.
When marking out where to position noggings, bear in mind that they can't be spaced more than 1200mm apart and that it's easiest to stagger them to avoid having to skew screws when securing them. Start by measuring the distance between your joists and cut the required number of noggings to size.
Draw a line down the centre of the nogging’s position on both of the joists it will join to. Then, measure and mark a pilot hole guide 40mm from the bottom and 40mm from the top on each side.
Drill pilot holes before securing the nogging with 100mm external timber drive screws. Repeat this process until all the noggings are in position.
Building the steps
Steps should be positioned on solid, level ground. Bear in mind that step stringers shouldn’t be spaced more than 450mm apart.
Hold each step stringer in position and mark the edges onto the frame. Measure the distance between the marks and cut sections of joist to the required length.
On the cut sections of joist, measure and mark out three evenly spaced pairs of pilot holes. Then, clamp the sections into place, drill the pilot holes and secure with two 100mm screws at each end.
Put your first step stringer into position, making sure that it is flush to both the top and the side of the frame. Mark out two evenly spaced pilot holes and drill through the side of the step stringer and into the joist.
Secure the step stringer in place with countersunk 100mm screws, repeat this process on all exposed sides of the stringer. To secure unexposed sides, drill a skewed pilot hole on each side before skewing the 100mm screws into position.
Drill a final screw through the support frame and into the back of each step stringer, being careful to avoid the other screws that are already in place.
Take a section of deck board and mark where the fascia will go. Use a set square to help you mark a clear line.
Lining up with the mark, use the chalk line to extend this mark across the width of the steps. Then, measure from the far end of the deck to the chalk line and cut a deck board to length.
Put the cut deck board into position in line with the chalk line. If you are attaching fascia boards to the decking, as we are here, then you’ll need to allow for an overhang.
Securing deck boards
When securing deck boards, pre-drill all fixing points with a 2mm bit to prevent damage and splitting. You can also countersink the fixing points to achieve a smoother finish.
Because this board is overhanging, screw through the third groove of the outside edge and fix with a 64mm decking screw. When fixing the rest of the boards, always use the second groove in from either side.
To ensure the boards are straight, secure with a screw in one end then move to the opposite end and then back again.
Include an expansion gap of between 5mm and 8mm between each board. Create a suitably sized spacer from an offcut of timber and use it to check that the gap between boards is equal all the way along.
Finishing the steps
Once the boards are all laid, measure the gap on the steps. Cut sections of joist to length. These will act as additional support for your steps and can be staggered into position and secured like the previous noggings in the frame.
To secure the boards to the step stringers, always start by securing all the risers first. Measure the width of the step from the outer edge and cut a piece of deck board to length. Make sure you allow for enough overhang on each end so that the board is flush with the fascia.
Hold the board flush with the top of the step stringer and predrill your holes. Then, secure in place with 64mm deck screws into the second groove on each side.
To secure the boards that will form the tread, drill one screw into the second groove and one directly down and into the riser below. Always place whole deck boards at the front of the step where the most pressure will be applied.
If you have gaps that need filling, start by measuring the gaps and marking the required size onto deck boards, remembering to allow for the 5-8mm expansion gap on either side.
Secure the board and create a clear chalk line. Cut along the line with a jigsaw.
Once the sections are cut, secure with deck screws into the centre of the board and the first groove, making sure the screws fix centrally into the step stringer below.
Adding fascia boards
Measure and cut the lengths of board that you need. Then, measure in 50mm from both ends and mark pilot holes into the second groove in from both sides. Repeat these marks at 600mm intervals down the length of the fascia.
When securing the fascia, make sure there is a gap of 5mm - 8mm between all boards. Drill the pilot holes before securing with 64mm decking screws.
If you need to add an angled board because your garden is sloping then start by attaching packers to the main joist frame, this will give you something to secure the fascia onto.
Take an offcut of deck board and slide it underneath the top fascia until it nearly makes contact with the ground, mark a line onto the top fascia to show its position.
Mark on the fascia where the far end of your angled board will be and measure along to your line on the top fascia.
Measure the distance between the end of the angled board and the ground, when doing this remove 5mm as you don’t want the board to be touching the ground at any point.
On the deck board you will be using as the fascia, mark where the full width board will end (this is where the angled section will begin) and where the angled board will end.
Connect the marks where the angled board will begin and end with a chalk line and cut down this mark with a circular saw.
Secure the board to the packers using 64mm deck screws and repeat this process for all other angled boards. For an attractive finish, and to aid drainage around your decking, simply add some gravel.
Finally, if you want to add railings or lighting to your raised deck, then you can follow our step by step ‘How to assemble deck railings’ or ‘How to install deck lighting’ guides.