Planning & preparation
- This guide outlines the method for installing a single level composite deck with a timber frame and horizontal deck board positioning. Bear in mind that other decking designs will require different techniques and joist spacing.
- Follow all installation guidelines in order for warranties to be valid.
- Before you begin construction, it is vital that you are aware of all building requirements and restrictions; check with your local planning office if you are unsure.
- When choosing the location of your deck, consider elements such as wind, shade and privacy.
- Start by planning your deck to scale on paper and try and be as accurate as possible. Remember to factor all necessary expansion gaps into your plans.
- Bear in mind when planning your deck that the length of the Wickes range of composite decking boards is 1.8 or 2.4 metres.
- The width of the Wickes range of composite decking board is 140mm. Ideally, plan the width of your deck to include only whole deck boards, as you want to avoid cutting a deck board lengthways if possible.
- Ensure the fall of your deck frame is 1:100 and running away from the house as this will aid water run-off.
- If you are going to build your decking next to a house, make sure it’s 150mm below the damp proof course and that you don’t cover any air bricks.
- It’s best that your boards arrive on site at least 72 hours before installation, to allow for the composite to acclimatise. When the boards arrive, lay them on a ground sheet and keep them covered.
Do it right
- If you are building a timber base frame, make sure that your timber is structurally treated.
- Ensure you leave a 40mm gap beneath fascia boards to allow for proper ventilation.
- Treat all cut ends of timber and drill holes with two coats of preservative.
- When drilling, it’s best to mark out pilot holes as this will help to make your fixings as accurate as possible. Ensure that you use screws specifically designed for the job and that all screws are secure but not over tightened.
- Whilst it is possible to build a composite deck on your own, it’s much easier with a spare pair of hands, so ask a friend if they can help out.
- If you need to cut a deck board to accommodate an obstacle, or you need to trim any overhanging deck boards in order to make a straight edge, mark a chalk guideline and then carefully cut along the line with a jigsaw.
- For information on ‘How to Build a Raised Deck’ see our video and online guide.
- For information on adding a wall plate, or further detail on joining joists, see our ‘How to Lay Decking’ online guide or video.
- Be sure to firmly secure timber and composite boards and take care when sawing or drilling.
- When drilling, wear safety goggles.
- Wear protective gloves when handling timber or applying wood preserver.
- Be sure to follow manufacturer’s instructions for drying and safety when using wood preserver.
- Wear safety goggles and a dust mask when using a jigsaw.
- Offcuts of treated timber or composite decking should never be burned, but need to be disposed of safely – your local recycling centre should be able to advise.
- Bear in mind that joists and composite products can be heavy, so take care or ask for assistance when moving them.
- Use a high-pressure hose to keep your deck looking clean and tidy. Keep the nozzle at least 300mm away from the boards when cleaning.
- Keep your decking clean and dry and remove anything that could cause stains, such as grease or oil, as soon as possible.
- Do not sand your composite deck boards.
Here are some examples of different decking designs. Remember to ensure the correct joist spacing dependant on the design you choose:
Preparing the area
An existing patio or concrete base can be used as a solid foundation for your composite decking. Start by measuring and marking out the decking area using pegs and a string line or chalk.
If laying the deck over lawn, mark out the area then dig out to a depth of 50mm. Cover the ground with landscaping fabric and add gravel. For soft ground, place paving stones in each corner, and halfway along where each joist will be.
Assembling the frame
If the deck you have planned is longer than your decking joists then you will need to extend them by joining sections together. See our section on ‘Extending joists’ before continuing.
Put your joists into position with any extended joists at the end where there will be least through traffic. If sides of your frame are hard to access, put the joist nearly into position but with enough room to be able to secure the screws. You can ask a friend for help to move the frame into its final position once the sections are secure.
To join the frame at each corner, first check that the corners are square using a carpenters square. Then, mark and drill pilot holes before using two 150mm timber drive screws at each end. Countersink the screws if you are adding a fascia.
Once the frame is secure, ensure that it is at the required level and place risers, paving slabs or treated offcuts of timber at 500mm intervals if needs be.
Assembling the inner frame
The positioning of your internal joists will be dependant on the decking design you have chosen. We are laying our arched boards horizontally so our joists need to be spaced every 300mm.
Measure and mark out the positioning of your joists onto the frame, making sure you never exceed the recommended spacing. Once you know how many internal joists you need, measure and cut accordingly. See our online guide or video for detailed instructions on extending internal joists.
Using a set square, extend your marker down onto the external face and mark two pilot holes, one 40mm from the top and one 40mm from the bottom. Drill the pilot holes using a 6mm wood drill bit. Drill countersink holes if you are adding a fascia.
Secure a joist in your workbench and attach joist hangers to both ends using 30mm external grade screws. Line the joist up with your spacer mark, ensuring it is flush with the exterior frame.
Line the joist up with your spacer mark, ensuring it is flush with the exterior frame and secure with 100mm timber drive screws.
If you have to secure the joist onto an unexposed side of the frame, drill a skewed pilot hole at a 45 degree angle then fix with a 100mm screw.
Once all the internal joists are in place, add the final 30mm screws to each joist hanger.
Measure out and prepare enough noggings so that the distance between them never exceeds 1200mm. Stagger the noggings to avoid having to skew screws.
Put the nogging into position and mark its centre point onto both joists it will join to. Then, mark and drill pilot holes 40mm from the top and 40mm from the bottom on both joists.
Secure the noggings with 100mm timber drive screws.
Laying your deck boards
Now it’s time to start laying your composite boards. If you have no overhang or you have a fixed deck, begin by fitting starter clips along the outside edge of the frame and secure with the provided screws and drill bit.
Or, if you are working with an overhang, as we are, put your first board into position, ensuring the overhang does not exceed 25mm. If you are adding a fascia, place an offcut of board under the overhang to ensure it will be flush to the fascia.
Measuring in 30mm from the edge of the board, pre-drill all fixing points using a 4mm drill bit. Secure to the joist below with composite decking screws.
With the first board in position, slide the hidden fastener clip into place so it sits within the groove of the deck board and is directly in the centre of the joist below. These fasteners secure the boards and ensure a consistent 6mm expansion gap.
Tighten the clip until it is 75% secure. Repeat this down the length of the board so there is a fastener clip at every joist.
Put the next board into position so that the fastener clips sit within the groove. Be sure not to push or force the board. Repeat the above process so there is a fastener clip at every joist.
Once the second board is 75% secure, finish tightening the screws in your first row, but be careful not to over tighten. Repeat the process of securing the previous row once the next board is in position. Then, secure the final board in the same method as you did the first.
If you are adding a fascia, start by measuring in 40mm from each end and creating two guide marks, one at 40mm from the top and one at 40mm from the bottom. Use a chalk line to connect the marks. Using the chalk line as a guide, mark at 300mm intervals down the length of the board.
Drill your pilot holes then put the fascia into position, ensuring a 40mm ventilation gap between the bottom of the fascia and the ground. Place packers underneath the fascia or ask someone to hold it level until it is secure.
Secure the fascia in place with 63mm colour coded composite decking screws.
Start by measuring and cutting the sections you need to reach the required length.
Measure and cut a 600mm section and mark at 300mm to show where the centre point is. Place the three sections into your workbench or saw horse and secure with clamps, making sure the 300mm mark lines up with the join of the joists.
Measure 75mm from each side of the join and mark the wood. Then measure 150mm from each side of the join and again, mark the wood. From each of the four marks, use a set square to draw a straight vertical line.
Mark two evenly spaced pilot holes onto each of the lines you have drawn. Drill pilot holes using a 6mm wood drill bit. Secure with 100mm timber drive screws. Countersink the screws if you are adding fascia boards later.
When extending the internal joists, repeat the same joining process as the outer frame, but with the addition of an extra 600mm section on the opposite side to sandwich the joist in place. Offset the bolts slightly so they don’t come into contact.
If you need two deck boards to meet end to end this will create a “butt” joint. All butt joints must sit on doubled up support joists that have a drainage gap of 10-25mm between them. Secure with four fastening clips, two at each end of the board, being sure to leave the recommended expansion gap between boards. Try and get the fastening clips as close to the edge of the boards as possible, as this will help the edges of the boards to look even.