Here is the short answer. If your garage roof is under ten years old and the leak comes from one identifiable fault, a repair is usually the sensible fix. If leaks are appearing in several places, the sheets or felt are visibly perished, or the roof is asbestos cement, replacement is almost always the better spend.
That one rule settles most cases. A £120 patch on a sound three-year-old felt roof is money well spent, but the same patch on a twenty-year-old roof that leaks again every winter is dead money, and on an asbestos cement roof it is not a safe option at all.
This guide shows you how to diagnose the leak by roof type, what repairs genuinely cost, and how to run the numbers so you only pay for the roof once.
First, Work Out Where the Water Is Getting In
Different roof types fail in different ways, and the fault pattern tells you most of what you need to know. Start with a dry-day look from a ladder, then check the underside for staining and drips.
- Felt flat roofs: look for blisters, splits at the edges and water that ponds after rain. Felt lasts roughly 10 to 15 years, so the age of the covering matters as much as the visible fault.
- Concrete and asbestos cement sheets: the usual culprits are cracked sheets, failed overlaps between sheets, rusted fixings and broken ridge caps letting water in at the apex.
- Steel sheets: leaks nearly always start at rusted fixings and perished washers, or as cut-edge corrosion creeping along the sheet ends of older roofs.
- Every roof type: blocked gutters make rainwater back up under the sheet laps. Clear them before you blame the roof itself.
If the garage went up before 2000 and has grey corrugated sheets, treat it as asbestos cement until proven otherwise. Our guide on how to tell if your garage roof is asbestos walks through the checks.
When a Repair Is the Right Call
Repair makes sense when the roof is young, the damage is isolated and the material is safe to work on. Typical honest repair jobs look like this:
- Patching a blister or split on a felt roof: £80 to £250.
- Swapping a handful of rusted fixings and washers on a steel roof, or replacing the odd damaged steel sheet: a quick, low-cost job.
- Clearing gutters and resealing a lap: maintenance rather than roofing, and often the whole cure.
On those terms a repair buys years of service for modest money. The catch is that repairs only stay cheap while they stay rare, which is where the maths below comes in.
Why Asbestos Cement Changes the Answer Completely
Asbestos cement cannot be patch-repaired safely. The sheets must never be drilled, cut or abraded, because that releases fibres, so the standard fixes for a cracked sheet or failed lap are simply off the table.
Swapping a single sheet rarely works either. Matching profiles are obsolete, disturbing forty-year-old fixings tends to crack the neighbouring sheets, and any work on the material carries legal asbestos handling duties.
Never power-wash or wire-brush an asbestos cement roof to tidy it up, and leave the moss alone. If an asbestos roof is leaking, the realistic answer is professional asbestos roof removal and a new roof. Our teams are UKATA trained and we are an Environment Agency registered waste carrier (CBDU516703), so the sheets are removed and disposed of legally.
Not sure which side of the line your roof falls on? Send a couple of photos through our free quote form and we will tell you honestly whether a repair is worth doing, with a free fixed price for replacement if it is not.
The Repair or Replace Maths
Two thresholds settle the numbers. If a repair would cost more than roughly 30 to 40 per cent of a replacement, or the roof is past two thirds of its expected life, replacement wins.
Watch the running-cost trap too. A £150 patch every year on a roof that would cost £1,200 to replace is dead money: within five winters you have spent more than half a new roof and still own the old one.
| Situation | Repair or replace | Why |
|---|---|---|
| One split or blister on felt under 10 years old | Repair | A £80 to £250 patch restores full service |
| Felt over 15 years old, ponding or multiple leaks | Replace | The felt is at end of life; patches will chase leaks |
| A few rusted fixings on an otherwise sound steel roof | Repair | New fixings and washers are quick and cheap |
| Cut-edge corrosion spreading along old steel sheets | Replace | Corrosion keeps advancing; the sheets are spent |
| Any leaking asbestos cement roof | Replace | No safe patch exists and single sheets rarely match |
| Water backing up from blocked gutters | Repair | Clear the gutters first; the roof may be fine |
Check the Hidden Damage Before You Decide
A leak rarely stops at the sheet. Press a screwdriver into the timber purlins near the wet patch: soft, dark or crumbling wood means the structure has been wet for months, and a patch on top will not save it.
Count what the water has already cost you as well. Rusting tools, mouldy boxes and a swollen side-door frame are part of the true price of leaving the leak, and they belong in your sums.
If the walls or base are failing along with the roof, a rebuild can beat a re-roof. In that case garage demolition and a fresh start is sometimes the cheaper long-term route, and we can price both options side by side.
What a Replacement Actually Gets You
A new roof ends the leak rather than postponing it. Our garage roof replacement service fits steel box-profile sheets backed by a 10-year workmanship guarantee, with the sheets themselves warrantied for up to 30 years.
Typical prices run from £950 to £1,800 for a new steel roof on a single garage, or £1,500 to £3,000 for a full asbestos strip and replacement package. Most jobs are finished in a single day.
You also get a garage you can actually use: dry storage, a roof your insurer will not argue about, and a tidier asset when you come to sell the house.
Free Assessment Across London and the South East
The Garage Roof Company is based in Chessington, Surrey and covers Greater London, Surrey, Kent, Sussex, Hampshire and Berkshire. We hold a 5.0 rating from more than 210 Google reviews.
Quotes are free and fixed, there is no deposit*, and you pay on completion. Call 0203 468 1242 and we will tell you straight whether your roof needs a £150 patch or a new roof altogether.
