The short answer
No. Foam sprayed on the underside of the tiles can slow the drip into the loft, but the fault above it is still there and the water simply goes somewhere you cannot see. The Energy Saving Trust does not recommend using foam on a leaking roof before the leak itself is cured. The leak should be repaired from outside, and the foam judged separately.
Why some firms offer foam as a leak repair
A leaking roof is stressful, and a quick offer to seal it from the loft sounds sensible. Foam goes on fast, fills gaps and sets, and the stain on the ceiling stops growing for a while. The sales pitch usually adds energy savings as a bonus, so one visit appears to solve two problems at once.
The trouble lies in what the foam is stuck to. A leak starts at the covering: a cracked or slipped tile, lead flashing that has failed, a tired valley, a broken ridge bedding. Foam underneath leaves every one of those untouched. Rain still enters at the same spot, and the foam only decides where it ends up. The owner is left with a roof that looks quiet and a defect that has simply gone out of sight.
What the Energy Saving Trust says
The Energy Saving Trust, on its roof and loft page revised in May 2026, describes firms that offer to deal with a damaged or leaking roof by foaming the underside before any repair, and states plainly that it does not advise this route. The same page adds a warning about rot: roof timbers can decay when water gets in or condensation builds up, and open-cell foam carries a much lower risk than the closed-cell kind.
That matters here because a rafter covered in foam cannot be seen or probed. If water keeps arriving from above, the timber behind the foam stays damp, and the foam masks the warning signs: stains, soft patches, a musty smell. Our guide to inspecting timbers under spray foam explains how we check them.
How a hidden leak shows itself later
Water that gets through the tiles and meets foam does not stop. It runs down the face of the foam, along a batten, or through any join between sprayed areas, and then appears at a wall plate, a ceiling edge or a chimney breast. A stain on the ceiling may appear far from the spot where water really enters, which makes the original fault harder to find than it was before anyone sprayed.
Meanwhile the tiles above sit on wet battens. Over a few seasons battens soften and nails lose their grip, so tiles that were only slightly slipped begin to move. Ceiling stains, peeling paint and a damp smell near the eaves are the usual signs. If you notice any of them in a house that has had foam applied, treat it as a reason for a survey, and do not add more foam to the problem.
Repairing the leak properly
A proper repair starts at the covering. Outside first, we examine the covering; then up in the loft we take photographs and follow the water back to where it starts. The cause is often small: a few cracked tiles, a lifted verge, flashing that has lifted away from a chimney. Many of those are repairs and not replacements, and we prefer to mend only what is actually broken.
Where foam covers the underside, a small area may need cutting back so the timber and underlay can be checked. After that the foam is a separate question. Some owners keep the insulation once the roof is dry and sound. Others decide to take it out, and our page on partial spray foam removal explains what a limited removal can and cannot achieve. When the covering itself is beyond repair, spray foam and a new roof sets out the next step.
If a surveyor has already raised it
Foam added to a leaking roof often comes to light during a sale. A surveyor notes it, the buyer's lender asks questions, and the owner has to explain a repair they may not have fully understood at the time. RICS advises talking to your mortgage provider and insurer, and says foam is something a valuer may weigh. A November 2024 press report said some lenders turned these homes down, while others assessed each case individually.
If that is your position, our page on what to do when a surveyor flags spray foam walks through the steps. A roof survey with photographs is often the most useful paper to hand to a buyer or lender, because it shows the actual condition and not a guess. The rest of the service is set out on our spray foam insulation removal page.
What it costs to put right
MyBuilder's roof repair guide, updated in August 2026, gives national bands of £100 to £300 for minor repairs, £500 to £1,000 for moderate ones and £2,500 or more for major ones. Its separate guide to removing foam quotes £20 to £50 per square metre, with an assessment at £100 to £200 and scaffolding at £500 to £1,500. Treat each as a general national guide and nothing more.
Your own figure depends on how much roof is foamed, how high the eaves stand and whether the covering must be lifted. Following the survey you get the quote in writing, with photos of your own roof attached. At the finish we clear up and cart the waste away, and you hold a 10-year workmanship guarantee in writing. Bring any paperwork from the foam installer to the survey as well, since it helps us see what was sprayed and when. To start, ring 01793 626096, message us on WhatsApp, or use the enquiry form.