How To Lay Decking

Laying a deck by yourself can be tricky if you’re not the most savvy DIYer, but it’s a great way to save money. In this guide, we’ll go through all the steps for laying your very own timber garden decking.


What you’ll need

Carefully plan the layout of your deck to avoid wastage. Work out exactly how much wood you’ll need taking into account the dimensions of the deck, room for expansion, and the size of the wood products.

Decking joistsScrews – 25mm, 30mm, 50mm, 64mm, 100mm, 150mm, 130mm (and washers)Drill
Decking boardsWall plugsWood drill bits: 2mm, 3mm, 6mm, 8mm
Decking spindles / panels (optional)150mm coach boltMasonry drill bit: 7mm
Handrail (optional)Joist hangersSocket set
Stringers (optional)Hammer
Decking postsSpirit level
Set square
Straight edge
Tape measure
String/builder’s line and pegs
Workbench with vice
Wood preservative
Hand saw / circular saw
Safety equipment: goggles, gloves, face mask

Important things to consider

Before you get going, there are some crucial questions to ask so you know what sort of design to work with and where to lay your decking:

  • How much sun will the deck get? – if you build in a shaded spot, your deck will need more maintenance as rain water will take longer to dry out which can weaken the timber in the long term.
  • Is the ground level or on a slope? – you may need to build a tiered deck on a slope.
  • What is the condition of the ground underneath? – very boggy and wet areas aren’t suitable for decking.
  • What is the view from the site? – are you peeking right over your neighbour’s fence?
  • How much privacy will you have? – would you be overlooked by your neighbours or tucked away at the back of your house?
  • Do you have any features to work with? – do you have trees, patios, and flower beds to work around?
  • Do you need planning permission? – check if you need to get planning permission for your deck.

Preparing the ground

You can lay your deck on grass, an existing patio, or concrete base.

Building on patio/concrete base

Measure and mark out the area you want your deck to cover. You can use weighted posts and string. If your deck will be square-shaped, measure each diagonal length of the area – if they are the same length, they are a perfect square. 

Building on grass

It’s not advised to build directly on top of grass so you will need to dig out some turf. 

Mark out the area you want with pegs and string. If your deck will be square-shaped, measure out each diagonal length of the area. If it’s the same length, it’s a perfect square.

Then use a straight edge to cut the perimeter of your square and dig out all the turf in the area. Dig the soil out to 50mm deep. Cover the area with a weed membrane and weigh it down with gravel. If your soil is particularly soft, place paving stones for extra support. Make sure the stones are all level with a spirit level.


Attaching to a house

If you’re building a freestanding deck, skip this step. If you are attaching it to your house, you need to create a “wall plate”.

Preparing the wall plate

If you have a sill under a door for example, your deck boards need to fit underneath it. Get a deck board and place it under the sill, and draw a line underneath. Use a spirit level and draw another line 10mm below this first line. This line accounts for expansion and will be the highest point the bottom of your deck board can be to fit.

Cut your joist to the length you need it to run along the wall. If there are obstacles like pipes, measure and cut out areas so the joist fits around it. Use two coats of wood preservative on all cut ends.

Mark a point 100mm from the end of your joist. Draw a line through this mark from the top to the bottom of the width of the joist. Then, measure and make marks 50mm down from the top of this line and 50mm up from the bottom – these will be your pilot holes. Repeat at 600mm intervals along the full length of the joist. At the end, measure 100mm from the end of the joist inwards like you did before, and repeat the process for marking the pilot holes.

Use an 6mm wood drill bit to drill the pilot holes.

Fixing the wall plate

Place the wall plate on the wall using your guidelines. You can have someone hold it or use timber offcut packers to hold it up. Check its level with a spirit level. Then check the deck board fits above the wall plate under the sill with a 10mm gap.

When you’re happy, drill guide holes through the wall plate with a 7mm masonry drill bit. Make sure you drill far enough that you make an indent on the wall itself. Then move the wall plate away and drill right into the wall. Insert wall plugs in the hole and gently hammer into place.

Place 130mm screws through your wall plate and washers on the back. Use enough washers to create a 10mm gap to allow water to run through. Hand tighten the screws and then use your drill to tighten it properly. Repeat this process to add a second plate to the wall if you need to avoid obstacles.


Building your external frame

Be sure to measure 3x to make sure you have everything correct!

Preparing the joists

Measure your joists – if you need the joist to be longer, cut down a second joist so it is the extra length you need. To join the two joists together, you need to cut a third piece to 600mm to join onto the back of where the two joists will join. Mark the 300mm centre point on the third piece. Secure the 3 sections together in a workbench vice.

Measure and mark 4 guidelines with a set square on the joists:

  • 75mm from each side of the join.
  • 150mm from each side of the join.

Draw two pilot holes evenly spaced apart on each of the two lines you’ve drawn. Drill through the pilot holes with a 6mm wood drill bit. Then secure the joists together using 100mm screws. If you’re going to use fascia boards, countersink the screws so the fascia boards can go on flush.

Repeat as necessary for all sides of your deck frame.

Attaching the joists

Before fixing the deck in place, the frame must be at the correct, even level. You can use treated offcuts of timber, paving slabs, or similar to raise up the joists at 500mm intervals. Check that it is level with a spirit level and that the corners are square with a set square.

To join the joists, mark and drill pilot holes. They should be evenly placed at the top and bottom of the joist so that it’ll be secure when the screws go through the joist into the next joist. Use two external grade 150mm timber drive screws and countersink if you’ll be adding a fascia.

For harder to access joist corners, you need to drill skewed pilot holes. To do this, you’ll drill in straight for a second and then angle the drill at 45 degrees. You’ll need 100mm external grade timber screws for these holes.


Completing the base frame

Now you have four pieces of wood joined to make your external base frame. You now need to add internal joists to support the decking boards.

How many internal joists?

To calculate the number of internal joists you need, mark 400mm from one side of your external joists. Keep making marks at 400mm intervals. If you get near the end and there’s a larger gap than 400mm, make another mark about halfway between your last mark and the end of the joist as it’s better to have a smaller gap than a gap larger than 400mm. The number of marks you have is the number of internal joists you need.

Extending joists

If your joists don’t quite reach from one side of the external frame to the other, you need to join a couple together like you may have done with the external frame. You follow the same process as joining the joists earlier, but you need an extra 600mm block of timber for more support. Your screws should be offset so they don’t touch.

Fitting internal joists

To fix your internal joists to the external joists, put the internal joist in your workbench and attach a joist hanger with 30mm screws.

Place the joist inside in the external frame, with the 400mm mark on your external frame lined up with the lengthwise centre of the internal joist. The top of all the joists needs to be flush, so use packers to raise the internal joist if it’s not.

Get a set square and draw a full line on the outside of the external joist from the 400mm mark. Measure up 40mm from the bottom and down 40mm from the top. Make marks and drill pilot holes with an 8mm wood drill bit. Then use 100mm screws to secure the two pieces together.

Repeat for all of your joists. Again, if you have areas that are a bit trickier to access, you’ll need to to skewed pilot holes.


Adding noggins

Noggins are extra pieces of support that join internal joists together, running in the opposite direction.

How many noggins?

There should be no more than 1200mm between noggins and they should be staggered so they are not directly above or below the noggins in the next row. This means you don’t need to skew the screws to avoid hitting screws.

Preparing the noggins

Measure the distance between the internal joists and cut down joists to size. Remember to sand down splinters and add preservative to the cut ends before installing.

Installing the noggins

Add the noggin in position and use packers if required to lift it up so it’s flush with the internal joists.

Draw a line with a set square on the side of both joists it will connect to. Mark 40mm from the bottom and 40mm from the top on both sides, and drill pilot holes. Then use 100mm screws to join it all together.

Check the whole structure is level and at 500mm intervals, add packers for extra support.


Laying deck boards

Now it’s time to lay your decking boards.

Preparing the decking boards

If your decking boards fit across the full length of your deck, then great! If not, you have to cut some down to size. If you need to cut them lengthwise, use a handsaw or circular saw. These boards will be placed at the end that people are least likely to walk on.

If you have any obstacles, use a jigsaw to cut the correct shape out of the required number of deck boards.

Installing decking boards

If you plan to add fascia boards, you’ll need to plan for the end decking board to overhang.

Drill pilot holes in your boards with a 2mm drill bit. We recommend countersinking the screws too for a smoother finish.

Use 64mm screws to hold the decking board in place. Do one at each end so you can ensure the board is straight and doesn’t get knocked at an angle when drilling. Repeat for the other pilot holes, one at each end. If you’re adding a fascia and have an overhanging board, drill more screws into the third groove of the board at regular intervals.

There should be a 5-8mm gap between all of your decking boards to allow for expansion. If you’re building a deck beside your house, make sure there’s a 10mm gap between your final board and the house.


Adding fascia boards

Fascia boards make the deck look more “complete” but are optional. Follow these steps if you are including a fascia. Remember if you are adding railings or steps, you may need to remove the fascia and reattach.

Preparing fascia boards

Measure and cut decking boards to fit the required spaces. There should be 5-8mm between all your fascia and other boards.

Mark 50mm from each end of the fascia board. Then measure and mark at 600mm intervals along. Predrill a hole in the second groove on each side.

Installing fascia boards

Position the fascia board against the external joist, underneath the overhanging top decking board.

Attach the board with 64mm decking screws.


Adding decking railings/panels

You need decking railings or panels if your deck is over 600mm in height. The top of the railing must be at least 1100mm above the decking boards.

How many deck posts?

The deck posts can’t be more than 1800mm apart. Measure each side of your deck and calculate how many you’ll need. You will need one at each corner minimum. 

Preparing deck posts

Measure and cut your deck posts to the height that you require. When you attach your handrail, it should be 1100mm from the top of the deck, so keep this in mind when you cut your post.

Measure the height of your deck. Measure and mark on your deck post the point it’ll rest on top of the deck. Measure the width of the post and how far in you’ll need to cut out a notch to fit into the deck. Use a handsaw or circular saw to cut a notch in the deck post.

Drill 2 centrally placed and evenly spaced pilot holes into the bottom, outside facing side of the deck posts.

Preparing deck boards/fascia

If you are attaching deck posts at intervals that aren’t just on the four corners, you will need to cut a notch out of the decking board and remove the fascia before attaching the additional deck posts. 

Measure and make a mark on both the decking board and the fascia where the notched post will sit. Remove the fascia and use a handsaw to cut out the right size piece for the post to fit flush.

Do the same on the decking board but cut with a jigsaw.

Attaching your deck posts

Drill a 150mm coach bolt into each of the pilot holes and tighten with a socket set.

Preparing the railing

You can buy ready-made spindles and decking panels at Stewart Timber. You can cut to size to fit the gap you need between the decking posts.

Place an L-shaped bracket (long side) in the filet slot of your handrail. Use 2x 25mm screws to secure it. Do this on the other side of the rail too.

Mark on the post where you want the top of the handrail to sit (remember it must be 900mm). Put the short side of the L-bracket on the deck post with the top of the bracket on the line you marked. Secure with 2x 25mm screws.

Fitting the spindles/decking panel

Position the spindles/decking panel so that it sits under the L-bracket on the deck post. Secure the top and bottom L-brackets with 2x 25mm screws each so your rail and post are attached.

Measure 25mm from the end of the rail and mark. Drill a countersunk 3mm pilot hole at a 30 degree angle. Use 2x 50mm screws to drill from the handrail into the post to give it extra security.


Building decking steps

There are UK building regulations you need to follow when building your deck stairs:

  • The width of the steps must be no less than 760mm.
  • If the stairs are wider than 900mm, you need a central step riser to keep the steps from collapsing in the middle.
  • The vertical distance between steps should be between 150mm and 180mm.
  • You need a handrail if the deck steps exceed 600mm if the steps are under 1m tall, you only need 1 handrail and if it’s over 1m, you need 2 handrails.

You also need to ensure you have a sturdy base for the steps so it doesn’t sink. Paving slabs are a good idea to rest the steps on.

Constructing the step frame

Unless you have a deck height that doesn’t fit pre-made stringers, you are best getting some pre-made stringers.

Cut two sections of deck joist cut-offs to the width you’d like your steps.

Attach them between the two stringers using two countersunk coach screws on each side, for both the top and bottom joist cut-offs. One of the joists should be attached vertically so it sits flat against the deck sub-frame. The other joists should be attached the other way, so it is flat like a step.

Attaching steps to the deck

Drill pilot holes through the step frame and deck sub-frame, 2 on each side. Then use 4 countersunk coach screws to secure the step frame to the deck sub-frame.

Attaching the steps to the step frame

Measure and cut deck boards for your step treads. Position them on top of the stringers and drill two pilot holes on each end of the deck board. Use 4x 50mm deck screws per deck board to attach the steps.

If you don’t want “open” stairs and want to fill the vertical gap between steps, measure and cut more deck boards to fit the gap. Attach these by drilling through the stringer into the side of the boards.

Attaching a handrail

You need to notch deck posts so they support the deck steps better. Measure and mark out the area of the post you need to notch out and use a jigsaw to score the post. Use a chisel to cut out the notch, then sand down rough parts and treat with wood preservative.

Fit the posts along the side of the steps with the step sitting in the notch. Drive two coach bolts in each post into the steps.

Position your handrail on parallel with the angle of the steps, on the outside face of the posts. Mark the outer post edges and cut with a jigsaw. Then bolt the rail to the posts.

To attach your spindles, follow the method for attaching spindles to the decking sub-frame.


Enjoy your new deck!

After all that hard labour, you can enjoy your lovely new deck.

Be sure to keep on top of deck maintenance to keep it fresh for years to come.

For all your decking materials, check out Stewart Timber’s decking range.

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