The short answer
A properly fixed heavy-duty tarpaulin can keep a roof dry for a few weeks, and sometimes a few months in mild weather, but it is not a long-term roof. Sunlight breaks the fabric down, wind wears at the edges and fixings, and moisture can collect underneath. Aim to have the permanent repair done as soon as the weather and materials allow, and check the sheet after every storm.
Why there is no single answer
How long a tarpaulin lasts depends on its quality, how it is fixed, which way the roof faces and what the weather does. A cheap blue sheet from a hardware shop can split in a few weeks of sun and wind. A heavy woven sheet with reinforced edges, wrapped round battens and screwed through into the rafters, can last much longer. Fixing matters as much as the material, because most failures are caused by wind getting under the edge and working the sheet loose, not by the fabric rotting.
What wears a tarpaulin out
Several forces act on a sheet at once.
- Sunlight. Ultraviolet breaks down the plastic coating and makes the fabric brittle and chalky.
- Wind. Flapping at corners and edges frays the weave and pulls on the fixings. A single loose corner can spread into a tear.
- Sharp edges. Broken tiles, nail points and ridge edges cut through the cover where it rubs.
- Water pooling. A sag that holds water adds weight and stretches the fabric.
- Frost. Cold stiffens the plastic and makes it crack at folds.
The problems under the sheet
A tarpaulin keeps rain out, but it also keeps air out. If the roof underneath is still wet, or warm air from the house rises into the loft, moisture can collect on the underside and be trapped. Left for weeks, that can feed mould in the insulation and timbers. Our guide on whether a roof leak can cause mould explains how fast it can start. Loft ventilation at the eaves and ridge, which the tarpaulin may be covering, can also be blocked, so condensation builds up in the roof space.
How to check and extend its life
Look at the sheet from the ground after every windy night or storm, using binoculars if needed. Check the corners and edges for fraying or lift, and check for pools of water. If a corner is working loose, ask your roofer to refix it rather than climbing up yourself. Inside, look at the ceilings and the loft for any new stains. A tarpaulin that is sagging, torn or lifting should be dealt with promptly, since it can come off in a gust and land on someone or something.
Where a tarpaulin has to stay for longer because of a wait for materials, the roofer can renew the fixings, add a second sheet or replace worn areas. That is a stopgap that needs watching, not a plan.
Flat roofs, pitched roofs and conservatories
The type of roof changes the picture. On a pitched tiled roof, a sheet can be pegged over the ridge and held down on both slopes, which makes it more secure. On a flat roof, a cover tends to pond and flap, and water that collects on it adds weight, so a flat roof usually needs a patch rather than a sheet. Over a conservatory or an outbuilding, a tarpaulin is awkward, because the frame was never meant to carry battens, and the cover can cut into sealed units.
Exposure matters as well, and so does the slope direction, since the side facing the prevailing south-westerly wind takes the worst of it. A sheet on a sheltered terraced roof lasts longer than one on an exposed gable on the edge of a field, where the wind gets under every fold. If you can see daylight at an edge, or hear flapping at night, the cover is already failing and the roofer should be told.
Why the permanent repair should not wait
Every week under a tarp, the original damage stays as it is. Lost tiles leave battens and felt exposed. Cracked flashings are still cracked. The longer a roof stays open, the more risk there is of water finding a way in at the edges of the cover, and of wet insulation and rotting timbers. An insurer may also expect the repair to be done within a reasonable time, so tell them what is happening. Our guide to temporary roof repairs and tarpaulins covers the wider picture.
What we do
When we fit a temporary cover, we fix it for the weather the forecast promises and tell you plainly how long we expect it to hold. Then we survey the damage, photograph it and price the permanent repair in writing, at a fixed price, so you can plan around materials and the weather. If you have a tarpaulin already in place from someone else and want it checked, we can look at it and tell you what we see. See our emergency and general roof repairs page for how we work.
Every roof is different. A free survey with photos settles it for yours.
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