What Is Garage Roof Replacement?
Garage roof replacement means taking off a worn-out garage roof and fitting a new one: usually a fresh timber deck or new sheeting, a waterproof membrane, edge trims and a way to get the water off into a gutter. In London the typical candidates are the single-storey garages beside interwar and post-war semis in outer boroughs, the prefabricated concrete garages at the end of gardens, and the rows of lock-up garages behind terraces and estates.
Many of those garages were built with corrugated asbestos cement sheet roofs, often between the 1950s and 1980s. Others have a felt roof on chipboard that has been patched for decades. Because garages are rarely heated or watched closely, leaks tend to go unnoticed until the deck has rotted or the sheets have cracked, which is why full replacement is more common here than repair.
Signs Your Garage Roof Needs Replacing
- Daylight visible through the roof, or water running down the inside walls onto stored belongings
- A sagging roof with water pooling in the dip, or a deck that flexes underfoot
- Felt that is cracked, crazed, bubbled or held down with patches of different ages
- Grey corrugated sheets that are brittle, mossy or cracked, which may contain asbestos
- Rust on metal sheets or fixings, with holes forming around the bolts
- Plans to convert the garage into a gym, office or workshop, which needs a warm, dry roof
- A roof that has been patched several times in recent years with no lasting result
Garage Roof Options Explained
- EPDM rubber membrane. A single sheet of rubber over a new OSB deck, with no seams on most single garages. It is quick to lay and needs no heat.
- GRP fibreglass. A laminated resin roof that can be walked on and neatly finished with trims. It needs dry weather and a good installer.
- Torch-on felt. A modern multi-layer reinforced felt system, much more durable than old shed-type felt, but it uses a naked flame, which some neighbours and insurers prefer to avoid close to houses.
- Box-profile or insulated sheeting. Steel or composite panels on prefabricated concrete garages and lock-ups. Anti-condensation lining stops drips inside.
- Asbestos removal and re-roof. Where the old roof is asbestos cement, the sheets are removed and disposed of as asbestos waste before the new roof goes on. Some contractors do this themselves; others bring in a specialist.
What to Include When Asking for a Quote
Give the garage's approximate outside length and width and say whether it is single or double, attached to the house, detached in the garden, or one of a row of lock-ups. Describe the current roof: felt on boards, corrugated grey sheets, plastic or metal sheets. If you suspect asbestos, say so up front; if you have an asbestos survey or test result, mention it. That decides whether the removal needs specialist handling, which is often the biggest variable in the price.
Explain how the garage will be used afterwards. Storage only needs a watertight roof, while a home office, gym or conversion needs insulation, possibly a warm roof build-up, and a check on whether the walls and lintels can support it. Mention access too: a garage reached only through the house or down a narrow side passage means more labour to carry materials in and waste out.
A clear quote specifies the membrane or sheet, the deck thickness, whether joists will be replaced or just checked, how the rainwater will be taken off, and what edge trims are being used. For asbestos roofs it should state who removes the sheets, how they will be wrapped and taken away, and that you will receive a waste consignment note.
How Much Does Garage Roof Replacement Cost?
| Job size | Typical cost |
|---|---|
| Single garage, strip felt and re-cover in EPDM or torch-on felt | £1,200 – £2,200 |
| Single garage with asbestos cement sheets removed and new roof fitted | £1,800 – £3,200 |
| Double garage, new joists, GRP or insulated warm roof | £3,000 – £5,000+ |
These are indicative ranges, not quotations. Asbestos testing, disposal fees, replacement joists, new gutters and access through the house all move the price. Rows of lock-up garages are usually priced per unit with a discount for several at once.
The Garage Roof Replacement Process: What to Expect
- Survey. The roofer measures the garage, checks the joists and walls and identifies the existing roof material, arranging a sample test if asbestos is suspected.
- Clearance. You clear the garage or move valuable items away from the work area; the roofer protects anything left.
- Strip. The old covering is removed. Asbestos cement sheets are taken off whole where possible, wrapped and removed as hazardous waste.
- Structure and deck. Rotten joists are replaced, firrings are added to give a proper fall, and a new deck is fixed.
- Covering and edges. The membrane or sheets are laid, trims and gutters are fitted and the site is cleared.
Planning Permission and Building Regulations
Replacing a garage roof with a similar roof does not normally need planning permission. Raising the height, changing a flat roof to a pitched one or converting the garage to living space may need consent, depending on the property and whether it sits in a conservation area. Check with your borough before changing the roof's shape.
Some small detached garages are exempt from Building Regulations, subject to conditions including size, use, construction and proximity to boundaries. Do not assume that storage use alone makes a garage exempt; check the proposed work with building control. Carefully controlled removal of intact asbestos-cement sheets may be non-licensed work, but the material, condition and method determine training, notification and licensing requirements. Arrange competent assessment and authorised waste disposal. The HSE asbestos guidance explains the rules.
How to Choose a Garage Roof Contractor
- Will you confirm whether my roof contains asbestos before quoting a final price?
- Who removes and disposes of asbestos sheets, and will I receive a consignment note?
- Which membrane or sheet system do you recommend for my garage, and why?
- Will you replace or strengthen the joists if they are undersized or rotten?
- How will you give the new roof a proper fall to the gutter?
- What guarantee do you offer on the materials and on your workmanship?
Frequently Asked Questions
How do I know if my garage roof contains asbestos?
Corrugated grey cement sheets on garages built before 2000 often contain asbestos, but you cannot tell by looking. A sample analysed by an accredited laboratory, or an asbestos survey, gives a definite answer.
Can I overlay my old garage roof instead of replacing it?
Sometimes a sound felt roof can be overlaid, but overlaying asbestos sheets or a rotten deck only hides the problem. Most contractors prefer to strip back so the deck and joists can be checked.
How long does a new garage roof last?
The system specification, installation, drainage and maintenance all affect service life. Compare the manufacturer warranty with the separate workmanship guarantee and ask what inspections or maintenance are needed to keep either valid.
Can I insulate my garage roof at the same time?
Yes. A warm roof build-up with insulation boards above the deck is the usual choice if the garage will be used as a room. It raises the roof height slightly, so check edges, flashings and any planning restrictions.