Building a raised deck will take some time and is trickier than laying standard decking at ground level, but if you want to build decking on a slope or uneven ground it’s the best way to do it. If you do your research and follow instructions, you and a friend or family member can build a raised deck over a few days. Here’s a simplified guide of the steps you’ll need to take. Plan carefully
It’s best to plan your raised deck by drawing it to scale on paper before you go and get supplies. This will help avoid wastage and making more cuts to timber than necessary. Prepare the area
Prepare the area according to the instructions we give in the FAQ ‘How to lay decking’. However, because you’re building a raised deck, you’ll need to add posts: Place a post in the corner of the frame you created with the pegs and string. Measure and mark out 100mm from each side. Dig out this soil to a depth of 700mm (watch out for cables or pipes). You should have a 300 x 300mm hole. Repeat for the other 3 corners. Using a brick bolster, split a concrete block in two. Put a section of the block in each hole. Get a length of post longer than you need and place one in each hole. You can cut it down later. Create props on each post to hold them in place until you’re ready to add a cement mix. Check that they’re level. When you’re happy that they are, secure them in place with a concrete mix, making sure you create a slope in the concrete so that rainwater runs away from each post. When the concrete is set, remove the props. Create a string line around each corner post and find the centre point between each. Place a timber batten at each point, ensuring that they’re not spaced any more than 1500mm apart. Make the outer frame Working from the corner where the deck will be at its highest above ground level, measure and mark on the post where the highest part of the frame will be. Measure from the far side of one post to the opposite and cut sections of joist to size. Line up a piece of joist with the mark you made and temporarily secure it. Factor in a 2mm fall for every metre of decking so rainwater can run off. Secure the frame to the other corner post, ensuring it’s at the right level. Do this for every side of the outer frame. Using 100mm coach screws with washers hanging on the end, secure each end of the four sections of frame. Mark out where the centre of the support posts will be and secure all of these posts to the frame, except the centre post. Add your central support joists. These should run in the same direction as the deck boards will run. You’ll need to measure from the inside of the frame on one side to the inside of the frame on the opposite side. Attach the joist in the same way as you did for the other posts. Repeat so the centre post is in between two sections of frame and secure the posts with concrete. Trim down all the posts to the correct height using a saw. Add your weed-control fabric and weigh down with gravel across the entire area. Add your joists Measure 400mm from the centre of the outer frame and mark a line. This will be where the first joist is positioned. Repeat at 400mm intervals down the length of the frame – if the last one will be more than 400mm, add another joist to create enough support. Attach a joist hanger to each end of the joist. Place the joist in position so the centre lines up with the 400mm spacer mark. Secure using external grade screws once you’re happy that the joist is flush with the frame. Lay your decking boards
Refer to our FAQ on how to lay decking to see how you should attach your decking boards. Remember: Always treat cut ends and pilot holes with decking preservative to keep your decking in good condition for as long as possible.
Building a raised deck isn’t a straightforward task. If you’d rather leave it to the professionals, get a range of quotes to help you get the best price and a high quality finish.