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How to lay decking on riser pedestals

Guide written by:
Lucas, Antique wood-worker, Gloucester

Lucas, Antique wood-worker, Gloucester

26 guides
Laying your deck on riser pedestals allows you lift the boards off the ground to your chosen height. In addition to making the job easier, risers also help to increase the lifespan of your deck and create an even surface without the use of wedges. Here's your step-by-step guide to fitting the perfect deck support!

Important features

  • Preparing the ground
  • Spacing out your risers
  • Installing the risers
  • Laying the joist frame
  • Laying the decking boards
  • Dealing with any issues
  • Finish and wood treatment

Why install your decking on risers?

Whether you plan on laying wood, composite or duckboard decking, you will need to install your boards on supports to raise them off the ground and protect them from damp. This is where riser pedestals come into play!

Required skills

Now widely used, anyone with a few tools and some DIY know-how can use this system to lay their decking. You will need to be know how to use a tape measure and spirit level, and be able to do simple calculations. The idea behind these support pedestals is very straightforward: the plastic risers are placed on the ground (on concrete slabs, earth, tiles, etc.) at set distances. Equipped with a base, the risers can be fixed to the ground if required or else can be left as a floating installation. The main advantage of this system is that the supports are fitted with adjustable screws meaning you can easily adjust the level of your deck.

Steps to follow

1. Preparing the ground
2. Spacing out your risers
3. Putting the riser pedestals in place
4. Laying the joist frame
5. Laying the decking boards
6. Dealing with any issues
7. Finishing and wood treatment


Tools and equipment


Equipment
  • Your decking screws must be suited to the surface material. This is an important investment that will ensure a sturdy installation. Ideally, opt for stainless steel decking screws with the right length for your frame. If you don't want your fixings to be visible, go for decking clips (these must also be suited to board type). Decking spacers should be inserted between boards to create an evenly spaced deck, with a minimum spacing of 3 mm.
  • Your risers must correspond to the desired height of your deck and should be strong enough to withstand heavy loads. The risers must be chosen according to their height and weight which will determine whether they have the right load capacity to support the weight of your terrace. Of course, the bigger the risers, the higher the price (usually given per m²). Please note that – with the exception of duckboard – all riser pedestals will be topped with joist frames which, in turn, serve to support the decking boards. Your joist frame and decking must always be made from the same type of wood. Choose a robust, durable and weather-resistant variety of wood.

Tools

Laying decking on risers in 7 steps

1. Preparing the ground

Riser pedestals can be laid on any type of surface: tiles, concrete slab, earth and so on. The most important factor is to make sure the ground is stable and that the land is not likely to move.

On non-built surfaces such as bare earth, you'll have to go for a floating installation meaning that your structure is held down by the weight of the deck. If you'd rather fasten down your risers, you can first lay a concrete foundation and then fix them in place.

You will also have to check that your surface is level. While minor irregularities can be dealt with, your terrain should otherwise be perfectly flat. On well-laid concrete or existing tiling, there shouldn't be any issues. However, if you are dealing with bare earth, make sure you work the ground in advance or lay down a fine concrete screed to create a level surface. If you decide against laying concrete, you will have to put down some geotextile fabric to prevent weed growth.

2. Spacing out the risers

You will have to decide on the overall height for your decking – whether this be to make it flush with your door or, if necessary, to install a step. Your chosen height will also dictate your choice of risers and joist frame.

The first step will be to calculate the number and type of riser pedestals and joists you need. Manufacturers will often indicate the number of risers required per m² so this needn't be complicated!

Next, you will have to work out the direction of your boards, according to how you want your deck to look. This will also help to determine the spacing of your risers.

3. Installing the risers

Lay out your risers at the chosen intervals, fasten them using the right fixing plugs (if necessary) and set them at the desired level. Don't forget to incorporate a slight slope to direct rainwater away from your house at an incline of approximately 2%.

Please note: the spacing of the risers depends on the thickness of your top boards but also the joists underneath, which serve to distribute weight evenly across the structure. Make sure you read the manufacturer's instructions and check all diagrams carefully. As a general rule, it is not recommended to leave more than 70 cm between two consecutive risers.

4. Laying the joist frame


Screw the joists onto the risers at right angles according to the direction of your decking boards. Use two screws for each joint and take great care not to damage the screw threads of the risers. To give your joist frame a longer service life, you might want to seal the upper side of the joists using a material such as roofing felt.

It is advisable to leave a gap of at least 10 cm between the ground and the decking boards in order to ensure the wood is well-ventilated.

5. Laying the decking boards


At this point, you're over the worst of it! All you now need to do is to lay your decking boards one by one, screwing them down to the joist frame. There are two possible ways to fasten down your boards: screws or clips. 

When it comes to screwing, it is essential that you pre-drill the boards. Handy tip: make yourself a drilling jig so you drill to the same depth every time, meaning the visible screws are all level. The screw heads should protrude slightly from the boards as drilling them in further will create a hollow where water can stagnate. Finally, each board should be fastened down using two screws at each end.

If you've positioned your risers well, you shouldn't run into any problems at this stage. For wooden decking, try to hide the least attractive boards at the edges or use them as end pieces which will be cut off.

One last piece of advice: when laying your decking, leave the ends of the boards untrimmed as you go. Once you've finished the whole job, you can then cut them all at the same time using a circular saw.

6. Dealing with any issues

If spacing out your risers hasn't gone completely to plan, or if your corners aren't quite even, you'll have to trim extra board to shape in order to complete your decking. Try not to have any uneven boards on show.

Sometimes individual boards can be crooked or deformed. Running a circular saw along the inside edge of these boards can help to relax the wood fibres and stabilise a board that is already in position.

7. Finishing and wood treatment

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Fix one or more boards along the vertical edge of the decking structure by screwing into the joists. If needed, strengthen the corners with brackets.

If your wood isn't treated, it's a good idea to apply varnish and an anti-humidity or anti-fungal treatment – especially on cut surfaces.

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Guide written by:

Lucas, Antique wood-worker, Gloucester 26 guides écrits

Lucas, Antique wood-worker, Gloucester

After some time busting my hump at construction, specifically at renovation, painting, carpentry, laying kitchen and bathroom tile, I decided to get my degree as a Carpenter. And I did well because nothing is more pleasant than working on a timber frame or designing a wooden house.

Everything about woodworking fascinates me, and building my own home in this material is one of my goals.

I’m also a follower of construction tools: I love to learn about innovations, the way they’re used, the tips and tricks, or the performances of each new tool on the market, whether it’s for woodworking or not. I would be happy to advise you and help you with your choices.

Happy Tinkering.

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