Planning, process & cost
Pergola construction explained, from footings to roof
A pergola looks simple. The parts you cannot see decide how long it stands straight.
A timber pergola is built from four layers: footings that anchor the posts, the posts themselves, main beams that span between them, and rafters or slats across the top. Get the footings and the post to beam joints right and the structure stays square for years. Most pergolas are completed in a few days once the design is agreed, and they can be left open, planted, or covered with a roof for year round use.
Footings and posts
Posts are either set into concrete, bolted onto post shoes fixed to a slab, or mounted on ground screws. Keeping end grain out of standing water is what stops the base of a post rotting, so shoes or a well drained setting are worth the extra care.
Post size depends on height and span. Too slender and the whole frame sways in wind once climbers add weight.
Beams and joints
Main beams run between posts, usually notched over them or bolted either side. Diagonal knee braces at the corners stop the frame racking. This is the part where a carpenter's joinery shows: tight joints and good bracing are the difference between a pergola that feels solid and one that creaks.
Rafters, slats and roof options
The top can be finished in several ways, each giving a different amount of shade and shelter.
- Open rafters: classic look, dappled shade, ideal for climbing plants.
- Close slats: more shade, still lets rain through.
- Clear roof sheets: shelter from rain while keeping light.
- Solid roof: effectively an outdoor room, with guttering needed.
Attached or freestanding
A pergola fixed to the house uses a wall plate on one side and posts on the other. It needs sound masonry and care around damp proof courses and windows. A freestanding pergola has four or more posts and can sit anywhere, over a patio, a hot tub or at the end of the garden.
Timber and finish
Pressure treated softwood is the common choice and can be stained or painted. Hardwoods such as oak cost more but weather to a silver grey and need less upkeep. Whatever the timber, cut ends should be treated on site.
Sizing a pergola properly
Size a pergola to the way you use the space. A dining table with chairs pulled out needs more room than people expect, and posts in the wrong place end up in the way of every chair. Head height matters too, especially if climbers will hang down from the rafters. Marking the post positions on the ground with canes before anything is ordered is a simple way to check it feels right.
Maintenance over the years
Check fixings and joints once a year, keep climbers tied in so they do not lever joints apart, and re-coat the timber as the finish weathers.
Questions we're asked about this
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