How to build a pergola

Video by Wickes. This guide draws on the popular Wickes tutorial "How to Build a Pergola | Wickes", which walks through the full build in a clear, practical way. Their section on fixing the cross beams at height is worth watching carefully before you start — it is the bit most people underestimate.

1. Plan the size and position carefully

Before you order a single length of timber, measure the space and work out how the pergola will sit in relation to your house, fences, and any overhanging trees. Most back gardens can fit a 3 m × 3 m structure comfortably, but even a metre either way changes how enclosed it feels.

Check with your local council if the pergola sits close to a boundary or if your property is listed. Most domestic pergolas fall within permitted development, but it is better to confirm than to dismantle.

2. Choose and order the right timber

Pressure-treated softwood is the go-to choice for UK outdoor structures. It handles rain, frost, and general British weather far better than untreated timber, and it is widely available at builders’ merchants and large DIY sheds.

For a standard pergola, you want 100 mm × 100 mm posts, 150 mm × 50 mm beams, and 100 mm × 50 mm rafters. The exact quantities depend on your span and rafter spacing — typically 400 mm to 600 mm apart gives a good balance of shade and structure without looking heavy.

3. Mark out post positions and dig the holes

Use string lines and a builder’s square to mark out the post positions accurately. Getting this right at the start saves a lot of frustration later. Four posts for a square or rectangular pergola — measure the diagonals and make sure they match before you dig anything.

Post holes should be at least 450 mm deep, ideally 600 mm if your soil is soft or sandy. A borrowed or hired post-hole borer makes this much quicker than a spade.

4. Set posts in concrete

Mix a bag of post-fix concrete per hole — the fast-setting type that you pour dry and add water to is perfectly adequate for pergola posts. Stand each post plumb using a spirit level on two faces, brace it with temporary battens, and leave it for at least 24 hours before taking the braces off.

That said, if you have a solid existing concrete base or paving, post-base brackets bolted into the concrete are a cleaner solution and keep the timber away from moisture. Both methods work. Pick the one that suits what you have got.

5. Fix the main beams

The two main beams run across the tops of the posts, spanning the width. Offer them up to the post tops — you will need a second pair of hands here — and secure them with structural coach screws or joist hanger brackets. Notching the posts to accept the beams is neater and stronger than surface fixing alone.

Check the beams are level before you commit. A beam out by even 10 mm will make the rafters awkward to fit and the finished pergola will look off.

6. Lay the rafters

The rafters span between the two main beams and run front to back. Mark the rafter positions on both beams at equal intervals, and fix each rafter with a pair of structural screws or joist hangers. Most people cut a small decorative profile on the rafter tails — a simple chamfer or a curved cut makes a real difference to how the finished structure looks.

Mind you, do not let the finishing details distract you from checking each rafter is square and at the same height. A string line pulled across the tops helps spot any rogues before they are fixed.

7. Treat and finish the timber

Even pressure-treated timber benefits from a coat of exterior wood preservative or stain once the structure is built. Pay particular attention to any cut ends, which are the most vulnerable to moisture ingress. A fence or decking treatment in a colour you like works perfectly well.

Two coats, brush applied on a dry day, will protect the timber through several winters without needing much attention.

When to call a handyman

Call Richard if the ground is awkward, the timber is heavy, you are not confident working at height to fix the beams, or you simply want it done properly without the weekend spent wrestling with posts in the rain. A pergola is a straightforward build, but the groundwork and beam-lifting stages are where things go wrong if you rush them.