How to build a raised deck

Planning your project

Before you can build your deck, there’s two essential tasks you need to do first.

1. Seek out planning permission

You might need planning permission if your deck is going to be more than 30 cm off the ground. Similarly, if your deck and other outbuildings (like a shed) covers more than 50% of your garden, you will need planning permission.

It’s always better to be safe than sorry. If you fail to secure planning permission, you might have to destroy your decking so play it safe and double check before you begin.

2. Work out how much decking you need

You need to do a couple of calculations to figure out how much decking you need to buy. Fortunately, they’re not too complicated and can be easily done with a calculator.

We’ve got more information about the sums you need to do here. 

What you need to build a raised deck

Make sure you have everything you need before you begin your DIY project. Here’s what you might need.

Tools

• Tape measure
• Builder’s line
• Spade to clear debris
• Drill
• Spirit level

Materials

• Decking joists
• Decking boards
• Decking screws
• Balustrades and steps
• Stainless steel washers
• Masonry bolts
• Quick-drying cement
• Weed control fabric
• Gravel
• Metal joist hangers
• Galvanised nails
• Coach screws and socket set 

How to build a raised deck

Raised decks are a great idea if you want an outdoor extension to your home or to create a floating deck to enjoy BBQs and the sunshine.

Here’s how to build a raised deck step by step including attaching it to a wall, building the deck frame, laying decking boards, attaching decking handrails and balustrades, and building deck steps.

1. Place pegs at the four corners of your deck and run a builder’s line between each peg to mark out the size and shape. Clear the area of leaves, rocks and general debris. You don’t necessarily need to remove the turf, that’s up to you.
2. Square the site. You can find out more about how to do that in the ‘How to square a site’ section.
3. If you want to attach your decking to a building, you need to fit one joist directly to the wall and align the rest of the sub-frame with it. Mark where you want to fix the joist to the wall making sure it won’t block air bricks or disrupt the damp proof course.
4. Before you attach the joist, you need to drill holes along its length. Alternate between drilling one hole at the top of the joist and one hole at the bottom of the joist, spacing them 400 mm apart. They shouldn’t be too close to the edge because this will weaken the joist. They also should be positioned so the bolts will eventually be secured to the brickwork and not the mortar and they shouldn’t coincide with the eventual position of the joist hangers.
5. Drill recesses into the joist with a flat wood bit. The recesses (otherwise called countersunk holes) need to be deep enough for the nuts and wide enough so you can comfortably tighten or loosen them with a spanner. Make sure you measure and drill accurately or else the bolts won’t work as they need to.
6. Position the joist against the wall (you might need some help with this) and use a spirit level to check it’s straight. Make a mark on the wall through each hole to indicate where you need to hang it.
7. Remove the joist and use the hammer action on your drill to drill through the brick at the marked points. Don’t do this unless you’re confident you’re drilling into the brick and not the mortar!
8. You need to leave a gap between the timber joist and the wall so water can run down the wall instead of pooling on the deck. You can make a spacer with a few stainless steel washers. When fitted together they need to measure a minimum of 10 mm.
9. Place the spacer between the joist and wall. You can do this by inserting expanding masonry bolts into each hole and tightening them with a socket spanner. Don’t over tighten the bolts.

Next comes the posts that support the joists. You will have four corner posts as well as joist support posts which are evenly dotted about the deck base.

This part is difficult on your own, so you might want to rope in some help.

1. Dig 700 mm deep holes in each of the corners you’ve marked out for your decking. The holes should be 400 mm wide at the bottom, and 300 mm wide at the top.
2. Your posts should be evenly spaced out and the centre of each post should be no more than 1.8 m apart in any given direction. Corner posts shouldn’t be right in the very corner but should be offset to one side by the width of a post. This is to make it easier when you come to installing railings or a balustrade.
3. Build props to help keep the posts upright. Grab two pieces of timber and form an L or T shape and spike the bottom so it will stick in the ground. Screw the other end to the post and use a spirit level to make sure the post is upright.
4. Pour quick-drying cement into the hole, shaping it so it slopes away from the post.
5. Once the concrete has set as per the instructions, remove all the lines, profiles (from squaring the site) and props.
6. Place a sheet of weed-control fabric down, making sure you cut it to fit around the posts. Cover it with gravel. 

How to square a site

Squaring a site means your decking will be perfectly square. You don’t want to have laid it in position and concreted the supporting joists only for you to later realise that it’s ever so slightly wonky.

Although you need to do this halfway through building your decking, it can be a long winded process so we’re including separate steps that are easy for you to follow.

1. Timber profiles will help you find the perfect right angle to form your square. They look a little bit like a three sided square. To make one, cut three 600 mm lengths of 22 mm x 100 mm timber. Make sure two of the three pieces are cut at an angle as these will be stakes that you need to drive into the ground. Hammer the third piece into place horizontally across the two stakes.
2. Take up the pegs and your builder’s lines. Hammer two of the profiles into the ground at each corner the area where your decking will be. The centre of the horizontal piece should be parallel with the edge of your cleared area.
3. Run a builder’s line from one profile to the opposite and tie it taut. Be careful to make sure it’s perfectly horizontal and not angled.
4. Run a builder’s line from each profile to its opposite and tie it taut. Check that it’s perfectly horizontal and not angled.
5. 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 the crossbeams are level.
6. Check the builder’s 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.
7. 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. 

How to build the joist sub-frame

Once your joist posts are securely in place and the concrete has set, you need to build the sub-frame of the deck. This is the section of the deck that the boards will sit on top of.

It’s really important that you know which deck design you’re going for by this point. The boards will run in the opposite direction of the joists, so you need to know how to lay the joists to get the final effect you want.

1. Cut the outer joists to length, leaving enough length for the corners to overlap with one joist end sitting flat on top the other joist. This will make it easier for you to attach the two together. Use end grain preserver to protect the cut ends from moisture.
2. If you’re fixing the deck to a wall, use metal joist hangers and 50 mm galvanised nails to attach the sub-frame joist to the wall joist. Drill pilot holes to ensure the wood doesn’t split. If you’re not fixing it to a wall, skip to the next step.
3. Line up the side joists with the outside of the corner posts. The ends should stick out by the width of a deck post so a railings post can be secured within the frame. Check the joist is level with a spirit level before affixing it.
4. Drill holes through the joist into the corner post and create a countersunk hole. Attach the joist to the post using two coach screws and a socket set with ratchet handle. The countersunk hole should mean the screw heads sit flush with the wood.
5. Create another countersunk hole and use two more coach screws to join the corners of the outer joists together. You should now have two joists secured to each other as well as the supporting posts and, if relevant, the wall too.
6. Repeat the process around the rest of the outer frame.
7. Your decking will probably be used quite a lot so you want it to be strong and secure. Screw one support beam (two in total) on either side of every second post using two coach screws. Position them directly below the joist of the sub-frame.
8. Once you’ve strengthened the deck, cut the inner joists to size and use two countersunk coach screws at either end to attach the joists to the frame. Use joist hangers if your deck is attached to the wall. If you’ve chosen a horizontal pattern, the centre of two inner joists should be no more than 450 mm apart. Diagonal boards need to have joists a maximum of 300 mm apart.

You should now have a supported deck frame, the next step is to add on the extras. 

How to fit decking balustrade

Railings should be added after you’ve built the sub-frame but before you’ve laid the decking boards. This is because you fit the deck boards around the support posts.

It’s up to you whether you add individual spindles, opt for a screen effect or add finishing touches like ball tops. Just like there’s a lot of ways to configure your decking boards, there are many different designs for railings, so make sure you do your research first and decide on a design before you begin.

Installing balustrades is simple.

1. You first need to decide how tall you want your railings to be. If you have small children, you might want to make sure the railings are tall enough so they can’t climb over them. You also need to remember to leave enough space below the base rail for the deck boards.
2. Decide how you want to space out the deck posts and cut the base and hand rails to length. We recommend 1.2 m as the absolute max so there’s no room for things (or people!) to squeeze through the gaps.
3. Drill pilot holes 100 mm apart along the base rail.
4. Slot the spindles into the grooved underside of the handrail. Screw diagonally through the spindle into the hand rail to secure them in place. If you want the spindles to be evenly spread out, use a block the same width as the distance you want for even spacing.
5. Drill pilot holes through the bottom of each spindle. Use 50 mm deck screws to attach the spindle to the base rail.
6. Insert a deck post in the gap between the support post and the corner of your sub-frame. Use a clamp or an extra pair of hands to hold it in place. Secure the post to the sub-frame with two countersunk coach screws.
7. To make the post you’ve just inserted more secure, fit a piece of joist offcut between the corner post and inner joist. Secure it in place with deck screws – this will prevent the post from moving.
8. Position the next deck post in another corner and secure it in place with one screw for now. This means you should be able to push it to one side as you secure the hand rail.
9. Use masking tape to mark a 12 mm drill bit 38 mm from the tip. Drill two holes to that depth at both ends of the hand and base rails.
10. Attach 12 mm wooden dowels into the first holes and mark the positions on the adjoining post at the top and bottom. Use your drill to make 38 mm holes in each mark.
11. Glue the wooden dowels into the post holes and slot the hand rail into place. Clamp the post and rail in place and leave it while the glue dries. Add a coach screw to the base of the second post to fix it in place. And that’s it! You have a constructed balustrade. 

How to lay decking boards on a raised deck

Once you have the frame and extras in place, you can lay the deck boards. This process is the same whether you’re building a raised deck or a flat deck, but there’s just a couple of extra steps.

1. Start at the outer edge of the sub-frame and move inwards. The boards need to be laid in the opposite direction to the joists so if you’ve gone wrong and the joists don’t work for your design, there’s either no going back or you’ll have to start again.
2. Cut the board to length and clamp it in position in front of the deck posts and so it overhangs the sub-frame.
3. Mark the outline of the deck post onto the deck board. Use a combination square to get this right.
4. Cut out the shape of the deck posts with a jigsaw. Treat the exposed cut end with an end grain protector.
5. Slot the board back into position. You might need to plane or saw down the outer length to ensure the inner edge is flush with the inside edge of the deck post. This will give you a perfectly straight edge to lay the rest of the boards against.
6. For the rest of the boards, see the how to lay deck boards section by clicking here. 

How to build decking steps to raised deck

The type of stairs and handrail you build depends on your decking. A low deck with stairs won’t need a handrail and open steps are fine, but a raised deck will need stairs and a handrail too.

Step kits are the easiest way to fit steps and will save you a lot of time. You can get them in set kits of three steps, four steps and six steps, so if you want a few more, you’re better off building your own. Here’s how to do that.

1. Your steps need to sit on firm ground otherwise they could sink and break. If the ground isn’t firm enough, create a small area of concrete or put a paving slab underneath the step.
2. Attach two joist offcuts the same width as the step treads to the step riser at the top and bottom with two countersunk coach screws on each side.
3. Position the steps against the frame of your deck, making sure it’s in the centre of the supportive pad or solid patch of ground. The longest edge should be on the paving slab and the shortest against the deck.
4. Drill pilot holes through the step frame and sub-frame joist. Screw the step frame securely to the decking with four countersunk coach screws.
5. Drill pilot holes at either end of the riser and secure the treads in place with two 50 mm deck screws. Repeat this process for each step.
6. If the tread you’re fitting is made of a solid composite board, you need to fit two boards on one step as they are narrower than timber treads. First, attach a start clip against the riser of each step. The riser is the vertical section.
7. Slide the first deck board into the clip and fit the universal fasteners to the front of the deck boards. This will create the necessary 6 mm expansion gap for the second board.
8. Position the second board and use 63 mm solid composite deck screws to screw the top of the second board into the riser. Repeat this process for each step.
9. If you want a solid stair instead of open gaps between steps, cut joist or deck board offcuts to size and screw them into the step riser with two screws at either end. 

How to fit decking handrail

A handrail completes your decking and ties it all together. Once you’ve finished this step, you can dust off the BBQ and admire your hard work.

1. You first need to secure notched posts at the top and bottom of your steps. Notched posts have a section removed so they can easily fit next to the steps. To create a notched post, measure and mark it with a square making sure the section is wide enough for the edge of the steps to slot into.
2. Use a jigsaw to score the post and remove that section with a chisel. Don’t remove more than half the post or you’ll weaken it and it may easily break.
3. Smooth down rough edges with a sandpaper and treat the exposed edge with Ronseal Decking End Grain Protector.
4. Secure two coach bolts through each notched post into the step riser.
5. Add a handrail to the outside of the posts, making sure it’s parallel with the angle of the steps.
6. Mark the line of the outer edges of the posts and cut along this with a jigsaw.
7. Bolt the handrail to the posts and check that the edges are neatly flushed.
8. If you want to add spindles, attach them to a base rail in the same way you would a handrail. Then cut the spindles to length and screw them in place.

Once you’ve built your decking you need to protect the wood from sunshine and rain. There are a lot of different ways you can do this, so we’ve created this guide for you to make the finishing touches easy.