Establish first whether the existing sheet is asbestos cement, which is common on garages built before the 1990s and must not be broken or drilled. After that it is a small flat roof: the deck condition, the falls and the edge details decide the work, and EPDM or GRP will both outlast the felt they replace.
- Corrugated cement sheet on an older garage may contain asbestos. Do not cut, drill or break it.
- The deck is usually what has failed, not just the covering.
- A garage roof is small, so the edge details are most of the job.
- A detached garage roof is normally exempt from Building Regulations; one attached to the house may not be.
Asbestos: check before anything else
This comes first because it changes who does the work and what it costs, and because getting it wrong has consequences that no saving justifies.
Garages built from roughly the 1950s to the 1980s very commonly have corrugated cement sheet roofs, and cement sheet of that period frequently contains asbestos. It is also found in flat garage roofs as a board beneath a felt covering, and in soffits and rainwater goods on the same buildings.
Asbestos cement in good condition is not dangerous while it is left alone. The fibres are bound in the cement. The risk comes from breaking, cutting, drilling, sanding or power-washing it, all of which release fibres.
You cannot identify it by looking. Asbestos and non-asbestos cement sheet look alike. Age is the best indicator, and the only certainty is a sample test, which is inexpensive.
It is not automatically a licensed job. Asbestos cement is usually lower-risk than some other asbestos materials, and removing intact sheets whole is often non-licensed work — but it still has to be done correctly, kept wet, not broken, double-bagged, and taken to a site licensed to receive it. It does not go in a skip or at the tip.
Get it tested first. If a contractor offers to rip an old cement sheet roof off without raising the question at all, that tells you something about how the rest of the job will be done.
Where the sheet is sound and the problem is elsewhere, leaving it in place and overboarding is sometimes an option worth discussing. Removal is not always the only answer.
What is usually wrong
| What you see | Usual cause | What it needs |
|---|---|---|
| Felt cracked and brittle all over | Age and UV; felt is the shortest-lived | Recover; check deck first |
| Sagging between joists | Deck has absorbed water | Replace the deck |
| Water standing after rain | No fall, or the deck has dropped | Firrings or tapered insulation |
| Leak at the house wall | Flashing stuck on rather than chased | Chase and dress a proper flashing |
| Leak at the edge | No drip; water tracks back underneath | New edge trim with a drip |
| Green growth and silt | Standing water and no maintenance | Clear; correct the fall |
| Corrugated sheet cracked | Age, impact, or walked on | Test for asbestos before touching |
| Daylight at the eaves | Rotten fascia or wall plate | Timber repair before covering |
On a garage the deck is more often the real failure than on a house roof, because garages are rarely inspected and a leak can run for years before anyone minds about a damp patch over a car.
Choosing a covering
For a small flat roof the realistic options are the same three used on any flat roof, and the differences matter less at this size than the detailing does. They are compared in full separately; the garage-specific points are these.
EPDM rubber suits garages well. A single sheet usually covers the whole roof with no joins at all on a typical garage, which removes the commonest failure point. It is forgiving of slight movement in a lightweight structure, and it goes down without heat.
GRP fibreglass gives a hard, seamless finish that takes foot traffic, which matters if the roof gets walked on. It is less tolerant of movement, and a lightweight garage structure moves more than a house does, so the deck has to be rigid and well fixed.
Torch-on felt is the cheapest and the shortest-lived, and it involves a naked flame on a timber structure. On a garage attached to a house, that is worth a thought.
Pitched options. Where the garage has a shallow pitched roof rather than a flat one, corrugated sheet, box profile or tiles may be appropriate, and replacing like with like is usually simplest.
For most domestic garages, EPDM on a sound deck is the sensible default: no joints, no flame, long life, and modest cost.
Regulations, boundaries and the neighbour
- A detached garage roof replacement is normally exempt from Building Regulations, being a repair to a small detached building. Replacing more than half the roof covering on a building that is not exempt can bring thermal upgrade requirements into play.
- A garage attached to the house, or one that has been converted into a habitable room, is a different case — it is part of the dwelling, and insulation and structural requirements apply.
- Garages on the boundary are extremely common, and the eaves or the roof edge often sits right at or over the line. Working on it may mean access from the neighbour's side, which needs their agreement.
- Where rainwater currently discharges onto a neighbour's land, a roof replacement is the moment to fix it rather than entrench it.
- Party wall considerations arise where the garage is built off a shared wall or where the work affects it.
- Asbestos disposal has its own requirements, and the waste transfer documentation is worth keeping.
- Listed buildings and conservation areas can control even outbuilding works, so check if either applies.
The access question is the one most often overlooked. A garage tight against a boundary fence can be awkward to strip and re-cover, and the neighbour finding out when the scaffold arrives is a poor start.
Worth doing at the same time
- Guttering and the downpipe. The roof is off and access is already there. Replacing tired guttering now costs a fraction of returning for it.
- Where the water goes. Many garage downpipes discharge straight onto the ground beside the wall, or onto a neighbour's land. Connecting to a gully or a soakaway solves a damp problem at the base of the wall.
- Insulation, if the garage is or might become a workshop, gym or office. Doing it as a warm deck during the re-cover is far cheaper than later.
- Power and lighting, if a supply is going in — the ceiling is open.
- The fascia and wall plate, which are frequently rotten where the roof has been leaking and are only accessible now.
- A roof light, if the garage is dark and you use it.
- Raising the edge detail, where the existing roof has always run water down the wall.
What it costs
These are the roofing figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Minor roof repair | from £150–£400 | Slipped or broken tiles, usually one day |
| Flat roof (EPDM / GRP) | £80–£120 per m² | Warm or cold deck |
| Full re-roof (typical semi) | £5,000–£9,000 | Strip, membrane, batten, re-tile |
| Chimney repointing / flashing | £300–£900 | Access dependent |
A garage sits at the lower end of the flat roofing figure because the area is small, but the fixed costs do not scale down — access, strip-out, disposal and the edge details are much the same whatever the size. Asbestos testing and licensed disposal are separate and are not included in any of the above.
We establish whether the existing sheet needs testing before anyone touches it, then check the deck rather than quoting from the ground.
Frequently asked questions
Does my garage roof contain asbestos?
Possibly, if it is corrugated cement sheet on a garage built between roughly the 1950s and 1980s. Asbestos and non-asbestos cement sheet look identical, so the only certainty is an inexpensive sample test. Do not cut, drill, break or power-wash it in the meantime — intact, it is not releasing fibres.
Can I remove an asbestos garage roof myself?
Asbestos cement is often non-licensed work, but it still has to be removed intact and kept wet, not broken, double-bagged and taken to a site licensed to receive it. It cannot go in a skip or to the tip. Given the disposal requirements, most people are better off having it done.
What is the best covering for a garage roof?
EPDM rubber for most domestic garages: a single sheet usually covers the whole roof with no joins, it tolerates the movement of a lightweight structure, and it goes down without a naked flame. GRP suits a roof that gets walked on. Felt is cheapest and shortest-lived.
Do I need building regulations for a garage roof?
A detached garage roof replacement is normally exempt, being a repair to a small detached building. A garage attached to the house, or one converted into a habitable room, is part of the dwelling and insulation and structural requirements apply.
Why does my garage roof sag?
The deck has absorbed water and lost strength, usually after a leak has run unnoticed for a long time — garages are rarely inspected and a damp patch over a car gets ignored. Re-covering over a soft deck reproduces the dip and ponds, so the deck needs replacing.
Should I replace the guttering at the same time?
Usually yes. Access is already there and the roof edge is open, so it costs a fraction of returning for it later. It is also the moment to deal with a downpipe discharging onto the ground beside the wall or onto a neighbour's land, which is a common cause of damp at the base.
Test first, then look at the deck
Two checks before any quote on an older garage: whether the sheet needs testing, and what condition the deck is actually in.