Can your pergola take a roof?
An open pergola only has to hold itself up. Once it's sheeted, wind pushes up under the roof and tries to lift it, and the posts, beams and their fixings have to resist that. Timber pergolas that have been out in the weather for years often have rot at the post bases or where beams sit on posts.
A builder or roofer will look at post size and spacing, the footings, the beam spans and how the whole thing ties to the house. Sometimes it's a matter of adding rafters and stronger fixings. Sometimes it's cheaper to keep the posts and replace everything above them.
Getting water off a flat pergola
Many pergolas are built dead flat. A roof needs a fall so rain runs to a gutter, and how much depends on the sheeting. Laserlite says its polycarbonate needs at least 5 degrees (88 mm of rise per metre), and BlueScope puts corrugated steel at a typical 5 degrees too, while concealed-fix steel can go much flatter. The usual fix is packing the rafters to create a slope, or raising one beam.
Then the water needs somewhere to go: a gutter on the low side and a downpipe to a drain. If the pergola attaches to the house, the join at the fascia or wall needs flashing, or water will run down the wall behind it.
Which roofing suits a pergola?
| Option | Good for | Watch for | |
|---|---|---|---|
| Polycarbonate sheets | Keeping light on the area and in the house | Clear sheets let heat through, and cheap grades yellow and go brittle | |
| Steel sheeting | Full shade and a long-lasting cover | Heat radiating down, and rain noise without insulation | |
| Insulated panels | Cool, quiet shade with a finished ceiling | Weight, so the frame may need upgrading | |
| Opening louvre roof | Choosing sun or shade on the day | Price, motor upkeep, and water at the blade edges in driving rain |
What you can check, and what to leave to a builder or roofer
You can
- Push a screwdriver into the base of each timber post from the ground to feel for soft, rotten wood
- Lay a long spirit level along the top beams to see whether there's any fall at all
- Ask your council whether roofing the pergola changes its approval status
Leave to a roofer
- Assessing whether the frame can take sheeting and wind
- Adding rafters, packing for fall, and stronger fixings
- Sheeting, flashing to the house, gutters and downpipes
- Replacing the frame above the posts if that's the better spend
What we'd do
We'd ask whoever quotes to price two options: roofing the existing frame with any upgrades it needs, and replacing the frame above the posts. On an old timber pergola the second one is often closer in price than people expect, and you end up with a structure built for a roof. For the sheeting itself, opal or tinted polycarbonate is a good middle ground if the area sits outside a living room.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.