Spray foam in a garage roof

A garage turned into a workshop, gym or home office needs warmth, and the roof is the biggest loss. Spray foam looks like a quick way to seal a corrugated or felted roof, with no boards to cut and no loft to give up. Some installers also use it to disguise a tired covering, which is the situation the Energy Saving Trust cautions about: spraying over a defective roof without mending it first is not something it recommends.

The roof may be pitched with tiles or felt, flat with a felt, EPDM or GRP membrane, or made of lightweight sheets. Each fails in its own way once foam coats the underside, and each calls for a slightly different inspection.

Plenty of older garages were roofed in asbestos cement sheeting, the grey corrugated panels that sit on purlins. HSE advice for anything built or refitted before the year 2000 is to presume asbestos is in the structure until proven otherwise. Foam sprayed beneath such sheets can disguise them completely, and cutting or scraping it away may disturb the sheet above.

In HSE terms, taking away asbestos cement is non-licensed work as long as it is lifted carefully rather than smashed. Once sheets are badly damaged or broken up, it turns into notifiable non-licensed work with added duties, and a householder's asbestos waste travels under a consignment note. Please never scrape foam from a garage roof you suspect is cement sheeting. Leave it undisturbed and have the material identified first. Our survey will tell you plainly if the sheets look like asbestos cement.

The same caution applies to soffits and boards around the eaves of an older garage. Some old boards contain asbestos too, and they can look just like modern ones, so a sample or a specialist opinion is safer than a guess.

An unheated garage swings between cold and damp air. Warm moist air from a car, a drying rack or a damp floor condenses on whatever is coldest, and with foam sealing the underside of a roof, that moisture can sit against felt, boards or timber. RICS says badly installed insulation can lead to dampness, including uncontrolled condensation.

For a store, nobody lives under the roof, so the cost of getting it wrong is lower than in a house. Still, a rotten deck must be replaced, and a garage that holds tools, bikes or a vehicle is no use with a sagging ceiling. Our notes on how spray foam is removed explain how foam is lifted from timber without damaging it.

Garage roofs can be treated differently from house roofs, and the answer turns on the size of the building, whether it is joined to the house and how the space is used, from storage to a studio. For a house, the Planning Portal says re-covering normally needs no building control application when under 25 per cent of the building envelope and under 50 per cent of the roof is affected. For a garage, ask the council or your building control body before you start.

Our page on spray foam removal and Building Regulations sets out the questions to ask. Should a job prove notifiable, we handle that notification and talk you through any consent first.

Planning is a separate matter. Swapping one covering for the same type seldom needs planning permission, yet a garage in a conservation area or tied to a listed house can be treated differently, and a call to the council's planning team beforehand is worth making.

MyBuilder's garage roof replacement guide, updated on 21 August 2026, gives a single flat garage roof at £700 to £1,000, a double flat roof at £900 to £1,400 and a pitched garage roof at £2,500 to £4,500. Foam removal at MyBuilder's £20 to £50 per square metre comes on top, along with disposal and any scaffold. These are national guides, and your garage may sit either side of them.

For a small flat roof, taking the foam off and re-covering the whole roof as one job is usually the sensible route. A pitched garage may need only its timbers checked. A written quote after the survey gives the figure for your building, so check whether it includes VAT.

A garage roof offers three realistic routes. Keep the foam, if the structure beneath is dry and the use is light. Strip it and put fresh insulation in, if you want a warm room. Or strip it and replace the whole covering, which is the cleanest result and often the least wasteful when the roof is old anyway. The right choice depends on what the survey shows, not on which option looks lowest on the day.

Think about use. A parked car needs little more than a dry roof. A workshop with a heater needs insulation, ventilation and a vapour plan. A room used by someone every day, such as a gym or an office, should be treated more like a house extension, with proper design from the start.

If the foam is in the house itself, a separate question arises, covered in whether the house will be colder after removal, and the timing of the work is covered by removing spray foam in winter.

For the garage, we inspect the roof from above and below, take pictures, and follow up with a quote on paper. Choose us and the work carries a decade of cover on workmanship, set out in writing, while the debris goes with us. Begin at spray foam insulation removal.