Raised decking is used to ensure that outdoor space is used to its full potential. Whether you want to reduce the amount of grass for garden care or a space for entertainment, you can find out how to install raised decking via this guide.


Table of contents:


What you need

Items below are what will be needed from start to finish, so please check what you need for the stage you’re at.

  • Decking boards
  • Tape measure
  • Mark square
  • Pencil
  • Deck fixings
  • Hammer
  • Jigsaw
  • Sandpaper
  • String/builder’s line
  • Tarpaulin
  • Pegs
  • Drill
  • Dowels
  • Quick-release clamp

How to prepare for a raised deck

You’ll need to make sure that you’re ready for your decking as you could end up with a wonky surface or worse. Before anything, you will also need to make sure there are no cables or pipes on or beneath the surface.

Step one: If the deck is being built more than 30cm off the ground or will cover over 50% of the garden space, you will need to make sure you have planning permission.

Note: Failing to get planning permission means the decking will need to be removed.

Step two: Plan the size of your future decking. This will play a part in what you purchase, so you’ll need to make sure you measure the site out; as you do use a builder’s line or string and some pegs to indicate the size and the corners.

You can measure in two ways:

  • Diagonally from post to post
  • Using a set square

Step three: Remove all the plants, rocks etc in the marked area – typically to a minimum depth of 50mm. Use an edger to clear any turf and remove grass with a spade; making sure to lift it in strips and place it somewhere unobstructive.

Note: Don’t throw it away if you plan to have greenery around the deck when finished as this could be used.

Squaring a site for raised decking

One of the most popular methods for squaring a site in preparation for a patio is the 3-4-5 method (aka 3-4-5 triangle method). This method is common in finding squares not only for decking, but many other projects. Here is how to use that method:

Step one: Start at one corner on one side and measure three (or a multiple of three) inches from that corner. Mark this measurement.

Step two: At the same corner, switch to the opposite side and measure four (or a multiple of four) inches from the corner. Mark this measurement.

Step three: Between the two marks made, measure the distance. If the distance is five (or a multiple of five) inches, you have your square.

This method is widely used because it is a simple version of the more commonly known Pythagoras theory.


How to build a raised deck

Starting with the outer frame:

Once you’re completely sure that there are no cables or pipes beneath the squared surface, you can start to create the deck – beginning with the outer frame! You might need some help with this so ensure you’re prepared.

Step one: You will need to begin by prepping a space for supporting posts for the joists. These will be offset to one side to ensure it’s easier to when installing railings or balustrades. In each corner of the squared space you’ve marked for the decking, dig holes around with the following measurements –

  • 700mm deep
  • 400mm wide at the bottom
  • 300mm wide at the top

Step two: Add the posts into the holes, making sure they are evenly spaced out with the centre of the individuals posts at maximum 1.8m apart. You must also make sure to add something to keep the posts standing in place.

Step three: Add the quick-drying cement into the corner holes dug in step one. You will need to shape it into place, sloping it away from the posts and waiting for it to set.

Step four: Once dry, remove the markings, post supporters and string from the squared area. Cover this area with weed control fabric, cutting holes in place to go around the standing posts, and cover the control fabric with gravel.

Building the sub-base/sub-frame

The sub frame will be the outer frame of the raised decking. The edging of the decking, if you will.

Step one: When cutting the joists to add to the outer frame, cut to length and allow for overlapping corner joints; using a brush to coat the ends of the newly cut timber with end grain preserve.

Step two: Place the side joists against the outside of each corner post. The ends should be sticking out width-wise of each post to ensure railings can be added inside the frame.

Note: use a spirit level to ensure the joist is level before securing it in place.

Step three: Create a countersunk hole (to ensure the screw heads are sitting flush with the wood) by drilling holes through the joists and into the corner posts. Using a ratchet handle, attach the timber joist to the post with two coach screws and a socket set.

Step four: Add a second countersunk hole, using two more coach screws to join the corners of the outer joists together.

At this point you should have two joists in place and attached to each other and the supporting posts. Repeat these steps for the rest of the outer frame.

Tip: If attaching it to a wall, place the sub-frame joist against the wall joist; attach with metal joist hangers and 50mm galvanized nails – drill pilot holes to ensure the wood doesn’t split.

Step five: To ensure the decking can withstand long-term use, screw a support beam either side every second post with two coach screws; positioning them directly below the joist attached to the sub-frame.

Step six: Cut the inner joists to side with two countersunk coach crews at each end. This will attach the joists to the outer frame. Remember, if attaching to the wall then use joist hangers.

If a horizontal pattern has been chosen, the centre of two inner joists must be maximum 450mm apart.

If a diagonal board pattern, joists must be maximum 300mm apart.

Fitting the balustrades

Balustrades must be installed before the decking and after sub-frame. They can also be various heights depending on your needs. Taller railings are advised; especially if small children are likely to use the deck to stop them from climbing over the side. Also make sure there is enough space for the deck boards to be added

Make sure to choose an ideal space between each deck post as well. 1.2m apart is typically recommended as it makes sure there is no risks for anything to fit through the space.

Now onto fitting the balustrades!

Step one: Along the base of the rail, use a drill to drill pilot holes around 100mm apart.

Step two: In the grooved underside of the handrail, insert spindles and secure them in place by screwing through them diagonally as this can ensure a firm fit. For even spacing, you can use a piece of timber equal to the distance wanted and evenly space out the spindles.

Step three: Once the spindles are installed, drill pilot holes through the bottom of each one and use 50mm deck screws to attach the spindles to the base rail.

Step four: Between the supporting post and the corner of the sub-frame, insert a deck post in the gap and use a clamp to keep it in place. Secure this post to the sub-frame using two countersunk coach screws.

To make sure the corner post is securely in place, fit a joist off-cut between this post and the first inner joist; then screw this to the sub-frame using deck screws.

You’ll need to place the next deck post then fix it using one coach screw so it can be pushed to one side while the balustrade is being installed.

Step five: Using masking tape, mark a 12mm drill bit 38mm from the tip of the post and drill two holes at that newly marked depth either end of the hand and base rails.

Step six: In the newly made holes, insert 12mm dowels and mark where the holes will be parallel on the adjoining posts at the top and the bottom.

Step seven: In each post, drill 38mm holes at the newly marked points then flue the wooden dowels into those holes. You can then slot the balustrade into place and use quick-release clamps to hold the post and balustrade together to keep them in place as the glue dries.

Step eight: To secure the second post, add another coach screw to the base and there you have it! A newly installed balustrade.

Laying boards for a raised deck

Time to get to the base!

Step one: Lay the boards starting at the outer edge of the sub-frame, moving inwards as you go.

Step two: To ensure the first board fits around the post you will need to cut notches into it. This can be done by cutting the board to length and clamping it into position in front of the deck posts. They will also need to be overhanging the sub frame.

Step three: Using a combination square, measure the outline of the deck posts and mark this onto the deck board. Then take the deck board off and clamp it face side up to a workbench to cut out the shape of the deck post with a jigsaw. Note: Ensure the cut edges are treated using a grain protector to ensure smoother fitting when out back in place.

Step four: Insert the newly cut deck board into position. If the board’s inner edge isn’t flush with the inside edge of the deck post, you will need to plane or saw down the outer length. With this in place, you can then work with a straight edge to lay the rest of the deck boards.


How to install raised decking steps

Step one: Firstly, you will need to make sure the area you plan to put the steps is level and firm as the steps could risk sinking in the ground and/or be unsafe to walk on. If the land isn’t firm, you can lay concrete or paving slabs in place for a more secure sitting place for your steps.

Step two: As a typical rule, you will need to cut two sections of joist off-cuts the width of the step treads and attach them to step rises – top and bottom- using two countersunk coach screws either side. This will be your step frame.

Step three: Place the step frame against the deck’s sub frame in the centre of the supporting area for your steps; ensuring the short edge of the step frame is against the deck.

Step four: Through the step assembly and sub-frame joist, drill pilot holes then screw the step assembly to the sub-frame using four countersunk coach screws for a secure fit.

Step five: Now to add the steps! For this you will need to drill pilot holes into each end of the riser and screw the treads into place using two 50mm deck screws. Continue this process until you have each step in place.

Note: For a solid stairway instead of an open stairway, fill gaps with joist off-cuts. You can do this by measuring the height and depth of the gap, then screw timber into the step rise using two screws each end.

How to fit hand railings to decking steps

If you’ve got steep steps or just want to add that little extra detail, consider adding a hand rail. This can complete the look and improve safety for when the steps are in use. During these steps you’ll learn how to create a notched post and how to install it in place.

Step one: On the posts you plan to add as hand rails, measure and mark the posts with a square.

Step two: Score the post with a jigsaw and use a chisel to remove the newly cut section – make sure you don’t remove over half the post. Removing over half can weaken it and risk breaking.

Step three: Smooth down any rough edges and newly cut edges with sandpaper. You can improve the appearance further by treating it with an end grain protector.

Step four: Install two coach bolts through the posts and into the step riser. On the outside face, place the length of the hand rail parallel to the angle of the steps and mark the line of the outer edges of the post using a pencil.

Step five: Cut along the pencil line with a jigsaw and bolt the hand rail to the posts. The edges should be flush.

Step six: Attach the spindles by fitting a base rail the same way you would a hand rail. Cut the spindles to length then screw them in place and there you have it! Newly installed step handrails.


How to install skirting panels beneath a raised deck

This is mostly a decorative option for those who want that little bit extra. However, it can also be used for the following:

  • Hiding anything if you want it as a storage space
  • Stopping children and pets from getting underneath the deck
  • Stopping stray wildlife from getting underneath the deck

Even if you need access to the space beneath, you can add easily removable sections to ensure there is a way to access in future if needs be.

Step one: To work out the size of panel you need, measure from the sub-frame down to the ground – this will give you the size needed.

Step two: Use a jigsaw to cut the lattice panel according to the measurements. If the panel has a frame, you will need to remove the frame batten from one of the discarded sections. You can do this by gently knocking the frame batten off the lattice using a hammer.

Step three: With 30mm galvanised screws, fix the batten to the cut edge of the lattice.

Note: You can add wire mesh to the inside facing side of the panel if you wish to further security beneath your decking.

Step four: To attach the panel to the deck, drill pilot holes into the upper frame and screw the upper frame of the panel into the deck sub frame with 65mm deck screws.

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