How to Build a Backyard Pergola: Simple DIY Woodworking Project

How to Build your Own Pergola?

Constructing A Pergola / November 4, 2019

A pergola is basically an open roof, set on posts or columns. They are great for encouraging trailing plants such as wisteria or honeysuckle to spread up and over them and providing welcome shade in a sunny patch.

Pergolas can be placed at the entrance to your garden, over a pathway, against a wall to shade a seating area or are ideal for framing an ornament.

How to build a pergola

You can buy pergolas in kit form, but they're quite easy to build from scratch using treated softwood. Make sure you paint the cut ends of the timbers and the feet of the posts with wood preservative before you start.

  1. Top tip - Hard surfaces

    Post supports let you put up a pergola or another garden structure on your concrete terrace or patio. Use a hammer-action drill and screw them firmly in place with expanding masonry bolts.

    Step 1

    Lay the three upright posts for one side of your pergola on the ground. Cut two lengths of timber to 1.22m and use them to mark the correct 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.

    Step 5

    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. Then saw off the marked wedge - or if you prefer, you could design a decorative profile of your own.

    Step 6

    Use the rafters as a guide to help you mark out the post holes. Square their ends with a length of timber and line them up exactly parallel using a 1.32m measure. This'll 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 7

    Fit the posts into the housings in the rafters. Then drill pilot holes and secure them with two 125mm galvanised nails.

    Top tip - Tight fit

    Your pergola posts should fit tightly into the housing in the rafters, so you'll need to tap them in with a wooden mallet. To avoid bruising the wood, hold an off-cut of timber between the mallet and rafter.

    Step 8

    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 9

    Raise one side of your pergola into the post holes and prop it up with temporary supports. Double-check the posts are vertical and in line with each other and that the rafter is level.

    Step 10

    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 and leave them to set for 48 hours.

How to fit the cross bars and trellis for a pergola

Trellis is optional on a pergola, but it'll help your plants to climb.

  1. Start by resting three crossbeams across the rafters at the post positions and nail them into position. Then nail the remaining four crossbeams in place, evenly spaced between the first three.

    Drill pilot holes and nail the first trellis panel into position using 65mm galvanised nails. Remember to leave a gap between the bottom of the trellis and the soil to avoid rot.