Building a pergola

Summary: Learn how to build a pergola, erect the uprights and fit the bearers and crossbeams.

A pergola is a timber structure used as a decorative garden feature designed to bear climbing plants. Before you purchase tools or materials for the pergola, make sure you are completely sure of the location, size and design of the structure.

There are two ways of anchoring the pergola uprights in the ground; metal post spikes which are driven into the ground with a sledgehammer; or concrete footings. The method you use will depend on the size and weight of the structure you are building and the type of ground you are building it on. Firm ground is suitable for the metal post spikes, but if your garden has light soil then it is advisable to anchor the uprights in concrete. When using metal post spikes use an off cut of timber to protect the top when driving them in to the ground.

This project looks at how to build a pergola that requires the uprights to be concreted into the ground.

Materials

You can buy pergola kits from most garden centres in a variety of styles. However, if you wish to make your own, you should use softwood timber treated with preservative. To build a basic pergola structure measuring 4m (13ft) L x 2.2 m (7ft) W x 2m (6ft 6in) H you will need:

6 posts 2.7m x 100mm x 100mm or (9ft x 4in x 4in)
2 bearers 4m x 100mm x 100mm (13ft x 4in x 4in)
5 cross-beams 2.2m x 100mm x 100mm or (7ft x 4in x 4in)

Marking out

  • Mark out the position of the uprights using wooden pegs. The uprights should be 1.5m (5ft) apart. Use a string between the two end uprights to ensure all three uprights are in line.
  • You will end up with 6 wooden pegs in the ground.

Erecting the uprights

  • Remove the pegs one at a time and dig the holes, which should be about 600mm (2ft) deep and 300mm (1ft) square.
  • A layer of gravel about 100mm (4in) deep in the bottom of each hole will prevent the bottom of the posts rotting and improve the drainage.
  • Mix the concrete: 1 part cement: 2 parts sand: 3 parts aggregate. The mix should be fairly dry, as it will support the post better than a wet mix.
  • Hold the upright in the hole while a helper shovels the concrete into the hole. Use a spirit level to check the post is vertical. Use a wooden stake to compact the concrete around the base of the posts and remove any air bubbles.
  • Concrete the end posts in first so you can run a string between them to ensure the centre is in line.
  • Before erecting the centre upright, tap a nail into the top of the end posts and run a string between them. Hold a spirit level against the line to check that the tops of the posts are level. If not you can lift a post slightly, compacting the concrete around it.  The string line will also act as a guideline for the top of the centre post.
  • It is a good idea to support the posts with temporary braces while the concrete sets, particularly in exposed locations.
  • The posts should be left for 2 to 3 days for the concrete to set.
Fix the two remaining crossbeams to the bearers using 80mm screws.

Fitting the bearers and crossbeams

  • Place the horizontal bearer along the top of the posts with an equal overhang at both ends. Use a spirit level to check that it is horizontal.
  • Mark the positions of the three posts on the bearer and the midway points between them.
  • Cut out five halving joints along the bearer using a mallet and chisel at the marked points. Cut them 100mm (4in) wide and 50mm (2in) deep. Do the same on the other bearer.
  • Now cut corresponding halving joints in the 5 crossbeams, allowing for an equal overhang of about 150mm (6in) at either end.
  • Put the bearers in position. The three crossbeams that join them to the posts are then fitted on top. Drill through the three pieces of timber and fix them in securely with either 200mm (8in) coach screws.
  • Fix the two remaining crossbeams to the bearers using 80mm  (3 ¼ in) screws.

Finishing

  • Having finished constructing the pergola, you can paint or stain it with your preferred finish. Some finishes can be poisonous to plants, so make sure you check before application.
  • Fixing screw-in vine eyes and wire to the pergola will assist plant growth on the structure.

Tools needed

  • Builder’s square
  • Spade
  • Spirit level
  • Spanners OR adjustable spanner

Materials needed

  • Builder’s square
  • Spade
  • Spirit level
  • Spanners OR adjustable spanner

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