How to Plan and Build Decking

Summer is here and many of us will be spending more time outdoors making the most of the (hopefully) good weather. BBQ’s, paddling pools and entertaining friends and family are no doubt part of many people’s weekend plans. Having a dedicated social area is a high priority on home improvement plans up and down the country. In this article we will take a look at how to design and plan a decking area to make the most of your outdoor entertaining.

Planning Practicalities

There are many practical things that need to be considered before you start to design your decking area:

1. Are there any services underneath the area to be decked? You don’t want to obstruct drain covers for example so you might need to build access into your design.
2. What are you likely to put on the decking? The foundations and supports will need to be very different if it is only people and tables that will be on the decking versus a hot tub for example.
3. Is the area to be decked level? Sloping areas can be decked but you will have to consider more supports if a part of the decking is to be raised off the ground.
4. Do you want the decking to be totally in sunlight or in the shade or a bit of both? You might need to build in some artificial shade if you do want a shaded area.
5. How big will the decked area be? You will need to factor in more supports and noggins if the area is bigger to ensure it is stable.
6. Does planning permission apply? You will need to check with the local planning team to be 100% but as a guide planning permission might apply if:
   • The deck is within 20m of a highway,
   • The deck platform is more than 300mm from the ground,
   • Any part of the deck exceeds 3m in height,
   • The deck could affect the privacy of neighbours,
   • The deck is to be attached to a listed building.
   • The decking along with all other extensions and outbuildings takes up more than 50% of the available garden area,

Once you have identified and dealt with the practicalities you can go ahead and start designing your fabulous new deck. Here are some best practice points to consider:

1. Always use structural treated timber for the decking. You do not want it unable to support the weight or rot too soon.
2. Ensure the Postcrete used for the support posts is piled slightly high and then sloped away from the supports to stop water accumulation.
3. Use specific screws and fixings for decking. These are specifically designed to be strong enough and weatherproof for your decking project.
4. Ideally raise the decking slightly off the ground to protect it from the wet, but at the least lay it on a self-draining gravel surface rather than on bare earth or grass.
5. Treat all cut edges with wood edge sealant.
6. When installing noggins, make sure they are staggered to allow you to screw them in.
7. Use the right sized structural timber:
   • Frame timber should be at least 150mm x 50mm.
   • Joists should be 100mm x 100mm.
8. Ensure you have the right spacing for the frame:
   • Structural support posts should be no more than 1800mm apart and around 1200mm apart for raised decks.
   • If you are putting heavy weights onto the deck supports should be even closer, around 600m apart to ensure the deck is strong enough.
   • Joists should be spaced at 400mm centres for the best support.
   • Noggins between joists, staggered in the centre of the joist.
   • Balustrades to be at least 90cm in height if the decking is up to 60cm from the ground and 120cm if the deck is higher than 60cm from the ground.

Once you have taken all this into account the best thing to do is measure the area you want and draw your design to scale marking down all the support posts, joists and noggins. Using this diagram, you will be able to accurately calculate the amount of wood you need for the subframe and you will also be able to calculate the number and length of decking boards you need.

Building Your Decking Area

For flat surfaces you will need to either build directly on to slabs or dig in some support posts to hold the decking slightly proud of the surface and therefore away from sitting water. You can build directly onto the surface but, if it is a grass area it is best to remove the grass, put down weed membrane and lay gravel to help drainage.

For raised decks, support posts should be buried to at least 600mm and cemented in with Postcrete to hold them in place. Make sure the posts are straight and level before cementing them in place.

The first thing to do is layout your frame and make sure it is square. The simplest way to do this is measure diagonally from corner to corner. The two diagonals should have the same measurement. If they don’t then the frame is not square. Once you have a square frame, screw the frame components together by first drilling a pilot hole and then screwing in the coach screws.

For a flat, ground level deck, cut blocks of the 100mm x 100mm support timber and place these in the corners. It is easier to cut them a little too long, so you have extra timber to allow you to level the frame. You can cut off the excess when your frame is level. Secure the frame onto the supports using coach screws. The procedure for a raised deck is the same, but you will need to dig a hole and cement the support post in place.

Once you have the frame in place, you can then start adding the joists and further support posts as required. Once all the joists and supports are in place, it is time to add the noggins to create the completed structure.

When putting the decking boards on, make sure that there is a 5mm gap between the boards for expansion. Use a simple spacer to do this. You can cut a piece of decking board for this.

Once you have put all the decking boards on, it is time to add the trim boards to the outside and then you are finished. Here is a great guide for building a basic low-level deck. Decking really is easy to build and if you are a relatively good DIYer it shouldn’t really tax you to your limits. With a little hard work and some upfront thinking and design, you will soon have a lovely area to enjoy entertaining this summer.