8 min read

How to build and install decking

5 October 2022

Garden decking is a perfect way to extend the usable living space of your home. Whether you’re making the most of an unused corner with a new seating area or creating a garden centrepiece in a sun trap, decking can instantly boost your garden’s usability for entertaining and relaxing. Although the project may seem daunting, with the right tools, quality timber materials, and the necessary know-how, it’s entirely possible to install a deck yourself. Read on to find out how to build a simple square garden deck with easy-to-follow steps

1. Planning Your Deck

The key to any DIY project is thorough planning and proper preparation. Before you begin work on your deck, make sure you’ve considered the following:

Sun and Shade – Are you looking forward to enjoying sunny summer evenings relaxing with a drink on your new garden deck? Spend a day watching the movement of the sun (and shade) across your garden and check that your proposed decking site isn’t in shade at the times you’re planning to use it.
Your Garden Layout – Give yourself plenty of space around bins, gates, sheds, and garden storage units, and be mindful of flower beds.
Garden Grates – Decks can be built above garden grates, but you’ll need to install a hatch for quick emergency access.
Garden Furniture – If you’ve already got your ideal garden furniture, lay this out (leaving room for chairs to be pulled out with a comfortable walkway) to get a realistic idea of the size your deck will need to be.
Damp Proof Course – If your deck will be attached to your house, make sure that it doesn’t lay above the property’s damp proof course.

Once you’re sure where you’d like to install your decking and the size it will be, take the time to properly plan out your deck, to scale, on a piece of paper. If you’re planning to use fascia boards around the edge of your deck, remember to factor their width into your plans at this stage.

Thorough planning will minimise time and material wastage and will help you to make an accurate order for your deck boards and timber, saving you from extra shopping trips mid-build.

If you’ve already got your eye on a particular style of decking board during the planning stages of your project, try to work your design around the board size where possible to avoid unnecessary cutting for a cleaner finish.

Once your materials arrive, it’s always worth carrying out a dry run. Lay out your frame timber, joists, and boards where you’re planning to build your deck as a last check that you’ve got everything you need.

2. Preparing the Ground

It’s important to prepare the ground beneath your new deck before you begin. It’s a relatively easy job and is essential for a long-lasting result.

Remove any loose stones, large weeds, or debris from the area. To make marking out your deck and digging out the earth easier, mow any overgrown grass.
Mark out the corners of your new deck with pegs and builder’s line to create a perimeter.
Use a shovel to dig out the earth within your perimeter line to a depth of 5cm. Use a spirit level to ensure the ground is level.
The ground should then be compacted. A soil compactor will do the job well, but a tamper should be suitable.
To prevent grass and weeds from growing through to your deck, and to maintain proper water drainage, lay down an even layer of landscaping fabric.
Distribute a layer of gravel across the landscaping fabric to bring your decking area back in line with the ground, creating a sturdy foundation for your deck.

3. How to Build a Deck Frame

A deck is comprised of a frame, joists, and boards. To begin assembly, you’ll need to create a simple perimeter frame using structural grade carcassing timber.

Take final measurements of your timber and cut your frame to size.
Coach screws in countersunk holes will leave you with the neatest finish. Working around the frame one corner at a time, drill holes ready for your screws in the outer piece of timber.
Line up your second piece of timber to create a corner, drill a pilot hole through both pieces of wood and insert and tighten screws as required.
Once all corners have been constructed, you’ve got your deck frame. Measure the frame diagonally to ensure it’s square before installing the joists or boards.

4. Fitting the Joists

Decking joists are lengths of pressure-treated timber fixed across the inside of your decking frame, increasing the deck’s load-bearing strength, and creating a sturdy base to which the decking boards can be attached. At Arnold Laver we have C16 or C24 timber suitable for outdoor use.

Working from the centre of your frame outwards, space joists 400mm apart from centre to centre for horizontal decking boards (amend this to 300mm increments for diagonal boards/composite decking).
For extra stability, you should run the joists in the opposite direction to the boards you’ll be laying on top.
Drill two pilot holes through the outside of the frame into the joist timber and fix into place with the appropriate size coach screw.
If you’re planning to use composite deck boards, ensure where the boards join you double up on joists and insert the appropriate deck clips for stability and strength.

5. Fitting Decking Boards

You’re almost there – if your frame and joists are sound and accurately measured, attaching your decking boards is a straightforward process.

Position your deck boards on top of your frame and joists leaving a gap of 3mm between boards. This small gap will allow rainwater to pass through to the ground below and create enough space for boards to expand and contract with temperature changes.
If your deck frame is larger than the length of a single board, make sure to position any joins directly above a joist to allow for a fixture point on both boards. For a neater finish, alternate where any joins fall so that they’re not side by side.
Use decking screws to attach your boards securely to the frame and joists below, with two screws into each joist and another two at either end into the frame. Remember to drill a pilot hole to prevent splits in your boards. Screws should be placed at least 15mm from the edge of the board.
Apply a preservative to any exposed edges and sand down any visible edge splinters.

6. Finishing Up

While landscaping timber should always be pre-treated, if you’ve chosen to install your deck in a perennially shaded area, bear in mind that it will need to be cleaned and treated more often than a deck that sits in the sun (you should expect to renew treatments annually if your deck is in a damp area/shaded/beneath trees).

Timber decks can be stained or painted in a range of contemporary and classic shades to complement existing garden buildings or fences. Even if you’re happy with the current colour of your deck, a wood treatment will help to protect the deck against rot and decay.

Congratulations, you have a finished deck! Now it’s time to sit back and take advantage of your new garden space.

Take a look at our full range of inspirational Decking ideas.