How to build decking on a slope in the UK

decking for sloped garden

One of the great things about building a deck in your garden is you can pretty much place it on any surface! While they’re most commonly built on flat surfaces, you can choose build your deck in order to even out the terrain on certain parts of your garden, or to make more sharply sloping parts it more accessible. Taking on this kind of project can be an attractive way to enhance your space and as an added bonus, it may also increase your property’s value.

Our guide will help give you an overview of what to expect if you’re planning on building a deck on slope.

Make a plan

Even if you’ve suddenly been struck with inspiration to build a deck in your sloped garden, we always recommend you take some time to plan your project.

The first step is to decide where you’ll ideally want your new deck. We recommend you use stakes and string to plot out your working area. It’s a good idea to plan your deck by making it the same length as the decking boards if at all possible — this way you can minimise cutting things to size! Be sure to allow for a 5-8mm gap between boards for expansion during periods of extreme weather.

You may also want to measure the height of the slope so you can accurately plan any stairs or steps. Once you finish your plan, you can use our handy decking kit calculator to find out how much decking you’ll need.

Prepare the decking area

Before you begin building your deck, you’ll first need to clear the area. That means removing the top layer of grass, foliage, and soil in the area you’ve marked for your new deck.

Be sure to dig to at least 50mm deep across the whole surface. Once you’ve completed that, you’ll need to mark where your posts will go and dig those holes. Put your posts in and make sure they are completely vertical using a spirit level. Now, you’re ready to set them! You’ll need to set them with concrete, although different types of concrete come with different sets of instructions. Mix your concrete according to the manufacturer’s instructions, and use it to secure your posts.

Build the frame

Once the concrete has set around your posts, it’s time to put in the centre point posts. Insert them dead centre, in between your existing corner posts. Dig a hole and insert a concrete block — but don’t put any posts in just yet!

We always recommend you start building the frame at the highest point of the deck. This way you can be certain of the frame height in relation to the uneven ground, so you can rest assured that it’s level!

fathers day present father and son working on decking

From here you can start to build and screw in a temporary frame. Be sure to include a slight slope for rainwater on your deck; typically a 2mm fall for every metre of decking. Once your temporary frame is complete go back to the centre posts with concrete blocks in them and put in a post. Check to make sure the post is vertical and clamp it into place. Secure the centre post in the same way you’ve done before and repeat until all centre posts are complete!

Now for the joists

After you’ve built the exterior frame, you’ll be able to start adding in the joists. This next step requires a lot of measuring! Be sure to put in your joists down the centre of your deck for the maximum amount of support. Once you’ve completed your centre joist, you can then measure the length inside, and then cut all your joists to match.

Next, you’ll need to find the centre point of the area that needs long joists (that you’ve already cut) and mark it. From there, you’ll need to measure out in 400mm intervals all along that side, and do the same for either side of the centre joist.

Fix the metal joist hanger to one side of your first joist, and screw it into the wood. Once it’s secure, you can then proceed with hanging it to the frame. Make sure to follow your marked guides as you put in all of the joists.

Build your steps

Next you’ll want to build your steps! You might be wondering why you need to do this before you install your decking boards — this is because you’ll need to secure the step stringers to the frame.

When you secure stringers to your decking frame, be sure they aren’t more than 450mm apart. If you’re making a wide staircase, you may need to use three or four stringers to ensure your frame and stairs are secure.

Lay your decking boards

The last step in building your deck is laying the decking boards. Remember to pre-drill of your screw holes to prevent damage or splitting the boards. On the first board, be sure to screw in one side and then the other. Ensure you lay it straight, as this will be the guide for all other boards!

Fit Your Own Decking

When you lay the second board, be sure to include your expansion gap of 5mm to 8mm between each board. We recommend using a spacer or extra piece of wood to slide down between the boards to ensure it’s even. Then simply continue the process until your deck is complete.

Obviously, there’s other steps you can take after you lay the boards, including hanging fascia boards or securing a railing. It’s also worth mentioning that if your decking project has to be built more than 30cm above ground (or if the decking platforms will cover more than 50% of the garden) you’ll need to get planning permission!

There are many advantages of using decking to level out a slope, including the fact it may add value to your home and give you access to an otherwise unused area of your deck.

And if you’re looking for a quick, easy, and cost effective way to build a deck in your garden, take a look at our decking kits! Each kit comes with a full set of clear step-by-step instructions and all the fixings you’ll need to do the job.

At Savoy Timber, we even have a decking kit calculator to help you make sure you’ve got the right kit! If you’re still not sure or need additional advice, give us a call or pop into any of our DIY stores in PrestonBlackpool, and Wigan.