Step 1
Lay three upright posts for one side of your pergola on the ground. Cut two lengths of timber to 1.22m. Use them to mark the distance between the uprights, top and bottom.
Step 2
Lay a rafter in position, jutting 200mm from the edges of the outer posts. Then mark the outline of the post tops on the rafter. As the timbers may not be identical, it’s a good idea to number each upright and the rafter in pencil so you can match them up again. Repeat this process with the other side of the pergola.
Step 3
Cut out the housing with a saw, wood chisel and mallet. Make sure that it’s a neat, tight fit. Profile the ends of the rafters and crossbeams. Then measure 25mm down from the top and 75mm in from the outer edge. Draw a line between these points with a pencil and extend it square down the adjacent faces of the timber. Saw off the marked wedge – or you could design a decorative profile of your own.
Use post supports to put up a pergola on a concrete terrace or patio. Use a hammer-action drill and screw them firmly in place with expanding masonry bolts.
Step 4
Use the rafters as a guide to help you mark out the post holes. Square their ends and line them up exactly parallel using a 1.32m measure. This will give you the precise position for the centre of each post hole. Mark these with canes, then remove the timbers and dig the holes to a depth of 450mm.
Step 5
Fit the posts into the housings in the rafters. Then drill pilot holes and secure them with two 125mm galvanised nails.
Your pergola posts should fit tightly into the housing in the rafters, so you’ll need to tap them in with a wooden mallet. Hold an off-cut of timber between the mallet and rafter
Step 6
Use the 1.22m length of wood to space the uprights accurately and a try square to check they’re square to the rafter. After that, brace the structure with three lengths of timber.
Step 7
Raise one side of your pergola into the post holes and prop it up with temporary supports made from extra timber. Double-check the posts are vertical and in line with each other and that the rafter is level. Raise the other side of the pergola and use a spirit level to make sure both rafters are at the same height. You may have to adjust the depth of the holes when doing this. Finally, concrete the posts in (ensure you wear protective eyewear and gloves when working with the concrete) and leave them to set in place for 48 hours.
Step 8
Now add the cross bars and trellis. Start by resting three crossbeams across the rafters at the post positions and nail them into position. Nail the remaining four crossbeams in place, evenly spaced between the first three.
Step 9
Drill pilot holes and nail the first trellis panel into position using 65mm galvanised nails. Leave a gap between the bottom of the trellis and the soil to avoid rot. Finish the job by nailing the final three trellis panels into place.
