The short answer
It depends on the covering. Built-up or torch-on felt typically gives 10 to 20 years, EPDM rubber 20 to 30 years or more, GRP fibreglass 25 to 40 years, profiled metal sheet 40 years or more with maintenance, and slate or clay tiles many decades. These are typical ranges, not promises, and poor fixing or neglect shortens every one.
Lifespans by covering
The figures below come from published trade and manufacturer sources. Where those sources disagree we give a spread, and every number assumes the roof was laid properly on a sound deck. Treat them as typical, because exposure, drainage and workmanship all move them.
| Covering | Typical life | What shortens it |
|---|---|---|
| Torch-on or built-up felt | 10 to 20 years, longer for good three-layer systems | Thin cap sheet, ponding water, poor edge detail |
| EPDM rubber | 20 to 30 years or more | Punctures, weak seams, trapped water |
| GRP fibreglass | 25 to 40 years | Movement in the deck, cracking at joints, UV on a thin top coat |
| Profiled metal sheet | 40 years or more, with maintenance | Coastal or industrial air, scratched coating, rusting fixings |
| Concrete tiles | 30 to 50 years | Moss, fading, failed underlay |
| Natural slate | 75 to 100 years or more | Rusting nails, soft battens |
A few of these ranges overlap with differing sources. Felt is the clearest case: one cost guide puts a good felt job at around 20 years and a poor one at under 10, and that gap is the real message.
Flat garage roofs
A garage added after the house is often given a flat or near-flat roof, and the covering there lives a harder life than one on a slope. Water has nowhere to run quickly, so any dip in the deck holds a puddle. A standing puddle ages felt and soft membranes faster and finds its way through the weakest seam.
A flat roof is not truly flat. BS 6229:2018 recommends a minimum fall of 1:80 for drainage, with a design target of 1:40 so building tolerances and deflection do not stop the water moving. A roof laid with no fall at all, or one that has since sagged, will fall short of its typical life whatever covering it wears.
Rubber and fibreglass suit a small garage roof because they go down in one piece with few joints. Felt is cheaper and easier to repair in patches, but each lap is a seam to watch. Whatever covering yours has, trouble tends to start at the edges and along the junction with the house wall.
Pitched garage roofs and sheet roofs
Where a garage has a pitched roof, the covering is usually tile, slate or sheeting, and the long-lived materials can outlast the timber under them. Natural slate is quoted at 75 to 100 years or more, clay plain tiles at 40 to 60 years in one guide (others disagree), and concrete interlocking tiles at 30 to 50 years. For slate in particular, the nails and battens tend to fail before the stone, much as they do on a house.
Profiled metal sheet is the common choice for a plain garage or outbuilding. One supplier quotes 15 to 25 years before first maintenance and over 40 years overall in typical conditions, with other sources saying 40 to 70 years or more than 50. The coating and the fixings are what decide it, and coastal or industrial air shortens it. If yours has a slope, the options are laid out in pitched garage roofs.
The old cement sheet roof is different. Its age is rarely known and its condition says more than its date. If it is cracked, crumbling or heavy with growth, treat it as at or past the end, and read our note on removing asbestos sheets yourself before anyone climbs up.
What shortens a garage roof's life
Four faults do most of the damage, whatever the covering. The first is water that stays: blocked gutters, a deck that dips, a missing drip edge. The second is poor detail at the edges and the abutment with the house. The third is movement, because a garage built on shallow footings or a deck that flexes cracks rigid coverings. The fourth is plain neglect, since a roof nobody has looked at for ten winters can carry a small fault until it becomes a big one.
Shade and overhanging trees add moss, leaf litter and damp. A garage used as a workshop or for storing damp items can also suffer condensation underneath, which rots timber from the inside while the covering still looks fine.
The way a roof is fitted matters as much as what is fitted. MyBuilder warns that slate fixed badly can fail inside ten years, however good the stone, and the same logic applies to sheets that are under-fixed or membranes laid over a damp deck. A good covering badly laid is a short-lived roof.
Judging what is left
You can judge a garage roof's remaining life from a few clues. Look for cracks, curling or blistering in the covering, staining on the ceiling or walls inside, daylight at the joints, sagging, and plants rooting in the gutters. Several together suggest the covering is close to its typical limit, even if no drip has appeared yet.
Once a roof is in its last third, it helps to plan rather than wait for the first leak. Budgeting early lets you compare quotes calmly and choose the covering that suits how the garage is used. Not sure whether to patch it or replace it? Our guide on repairing or replacing a garage roof gives the rules we use.
We look at garage roofs across Bath and the surrounding towns, and a survey from us costs nothing. We photograph the roof you have and give a written fixed price afterwards. Whatever we fit comes with a ten-year written workmanship guarantee. For the wider picture on materials and costs, start at garage roof replacement.
