How to build decking

Make sure that the timber you buy has been suitably pressure-tested and weatherproofed. If you cut the timber, you will need to treat the cut ends with wood preserver as well.

• Mark out the decking area using string lines tied to stakes driven into the soil.
• Clear the decking area of any vegetation.
• Place the concrete slabs at least every metre (3ft 3in) around the marked out area.
• Place a spirit level between slabs to check that they are level. If not, pack gravel underneath to level them.
• Lay a weed proof membrane over the area, cutting around the slabs with scissors.
• Spread gravel around the slabs on top of the membrane to level out the surface.

• Using 75mm x 50mm (3in x 2in) timber joists build a timber frame to go around the perimeter of the decking area. These will act as bearers for the decking boards. The joists are fixed together with countersunk 75mm (3in) screws suitable for outdoor use. Joists that need to be secured to a wall can be fixed using 100mm (4in) masonry bolts.
• Check that the joists are level and come together at the corners at right angles. If your decking is square or rectangular in shape measure the diagonals to check that the frame is perfectly square (the measurements should be the same).
• Cut and fix more joists inside the frame at 400mm (1ft 3in) intervals.
• Position the first decking board on the edge of the frame furthest from the house and screw it to the frame with a screw in each corner.
• Position the next board leaving an expansion gap of 5mm (1/5in) between the boards.
• Continue to lay boards in this way, maintaining the width of each expansion gap with wooden wedges.
• The last board will need to be cut and scribed to fit against the wall. Remember to treat the sawn edges with wood preserver.
• Finally, conceal the framework with fascia boards screwed to the outside of frame.

To construct a raised decking, you will need to secure the platform to posts in the ground. These can be fixed to concrete with post brackets, or concreted into the ground.

• Make a decking frame to cover the decking area (see above).
• Support the frame on blocks or bricks to achieve the desired height using a spirit level to check that it is level.
• Where the frame needs to be fixed to a wall, mark the fixing points along the frame. Drill pilot holes through the frame for frame-fixings.

• Position the 100mm x 100mm (4in x 4in) posts at regular intervals inside the frame.
• Mark around the posts with a trowel.
• Remove the frame and dig out the holes you have marked for the posts. The hole should have a depth and width of 300mm (12in). The holes should be deeper if the decking is being raised high above the ground.
• Check the position of the holes by putting the framework back in place.
• When satisfied that the holes are in the right position, pour hardcore into the bottom of the hole to a depth of 100mm (4in).
• Lay a weed proof membrane over the area, cutting around the post holes with scissors.
• Secure the membrane with a layer of gravel, spreading the gravel out evenly.
• Position the posts in the holes and check that they are vertically plumb with a spirit level.

• Insert frame fixings into the holes in the frame, tapping them in with a hammer, and fix the frame to the wall.
• Attach the posts to the frame. The most secure method of doing this is to drill a hole through both post and frame, and butt them together with a nut and bolt.
• Pour concrete or post mix into the hole around the post and leave it to set.
• Saw off any excess timber to make the posts flush with the frame.

• Position the first decking board on the edge of the frame furthest from the house.
• Screw it to the frame with a decking screw in each corner.
• Position the next board leaving an expansion gap of 3-10mm (1/8-1/3in) between the boards.
• Maintain the gap with wooden wedges as you fix the other boards to the frame.
• Continue to lay boards in this way. The last board will need to be cut and scribed to fit against the wall. Remember to treat cut edges with wood preserver.
• Conceal the framework with fascia boards screwed to the frame.

If you are intending to install steps in the decking, you will need to make an opening between the sections of balustrade. Your balustrade kit should contain newel posts, handrails, and balusters or spindles. A raised decking kit will come with stringers and tread boards as well. Ensure your kit contains enough newel posts to place one each side of the steps as well as in the corners.

• Cut a 20mm (4/5in) rebate from the base of each newel.
• Position a newel at the end of each section of balustrade.
• Rest the newel on the decking and drill two holes through the base of the newel into the decking frame.
• Insert nuts and bolts to secure the newel to the frame.
• Cut the hand and base rails to fit between the newel posts.
• Position the rails and check they are level.
• Fix the rails with screws to the newel posts.
• Measure the required distance between spindles. This should be less than 100mm (4in) and cut a batten to this measurement.
• Use this as a template to position the spindles.
• Fix the top and bottom of each spindle in place with galvanised wood screws.

If the steps are being placed on soil, level and weedproof the surface. You could use a paving slab or gravel to do this. If you are using a kit, simply fix the stringer to the frame and screw treads onto the supports.

• To make your own stringer, measure the height of the deck to determine the total height of the stringer.
• To calculate the number of steps, divide the height by 175mm (7in) which is the usual height for risers. Round up or down if necessary to make whole steps e.g. 670mm (26in) divided by 175mm (7in) = 3.8 which rounds up to 4 steps.
• Divide the total height by the number of steps to determine the height of each riser e.g. 670mm (26in) divided by 4 = 167.5mm (61/2in).
• To work out the position of the treads, subtract the riser height from the total height e.g. 670mm (26in) minus 167.5mm (61/2in).
• Mark out the position of the risers and treads on the stringer using a ruler.
• Check the depth of timber for the treads supplied - usually about 25mm (1in) thick.
• Below your marked lines, draw lines to represent the bottom of the treads - usually 25mm (1in) below. These lines will be your horizontal cutting lines.
• The tread width should be roughly twice the riser height but may vary depending on your kit.
• Transfer this measurement onto the stringer to mark the position of the front edge of the first tread.
• To work out the edges of the tread below subtract an overhang of 25mm (1in). The top step may not have an overhang as it connects with the decking.
• Then subtract the thickness of the risers. Transfer this measurement onto the stringer to give you the vertical cutting line.
• Continue in this way to calculate and mark out the position of the front edges of the treads.
• Draw a line connecting your horizontal tread markings.
• Draw a second line parallel to the first 285mm (11¼ in) below it.
• Complete the outline of the stringer by connecting up the parallel line with the top tread and bottom riser to make a whole shape.
• Check that the angles are 90° with a square.
• Cut out the stringer using a jigsaw and use it as a template for the second stringer.

• Fix the top of the stringers to the deck.
• If you wish to secure the bottom of the stringers, fix them to posts in the ground or use an angled bracket to fix onto concrete.
• Install riser boards (optional), securing them with nails or an angle bracket.
• Screw or bracket down the treads onto the stringers.