A stain on the garage ceiling, a drip onto the workbench, a corner of felt flapping in the wind: each of these raises the same question. Is it worth mending, or is the roof finished? The honest answer depends on what is wrong and where. A single split at an edge on a sound roof is a repair, and a spongy deck under a worn covering is not. This guide lays out how we tell the difference when we survey a garage roof, so you can apply the same tests, spot a quote that recommends too much or too little, and make the call with the facts in front of you.
The first question: what is under the covering?
The covering is what you see, but the deck and frame beneath it decide whether a repair can last. On a flat garage roof the deck is boards, usually plywood or OSB or older tongue-and-groove, laid over joists. On a pitched roof it may be battens on rafters, or boards under a felt. A repair needs something firm to bond to. If the deck is dry and sound, a patch will hold. If it is wet, soft or crumbling, the patch is stuck to a surface that is failing, and the leak will return in a different place.
You can sometimes tell from inside. Look up at the ceiling or the underside of the deck with a torch. Dark staining, flaking timber, fungal growth or white salt marks show a deck that has been wet for some time. Press gently with a screwdriver on a stained board: if it sinks in, the timber has gone. From above, a roof that feels spongy or bouncy underfoot is giving the same message. Our answer on rotten garage roof joists explains how to read the signs and what it takes to put them right.
Signs that point to repair
A repair is the right answer when the fault is local and the rest of the roof is healthy. These situations usually qualify:
- A single split, puncture or tear in a membrane or felt, with the surrounding covering flat, sound and well bonded.
- A failed sealant joint or loose flashing where the roof meets a house wall.
- A lifted edge trim, a damaged drip edge or a blocked outlet.
- A slipped or cracked tile or slate on a pitched roof, with the battens and underlay intact.
- A loose or missing fixing on a sheet roof, where the sheet itself is undamaged.
- A recent leak with a clear cause that can be seen, reached and fixed.
In those cases a repair is likely to cost a small fraction of a new roof, and it can return a roof to service for years. The condition is that the rest of the roof can carry on. Repairing one corner of a covering that is brittle everywhere is spending money to postpone a decision.
Signs that point to replacement
Replacement is the right answer when the damage is widespread or the structure is compromised. Look for these:
- A soft, spongy or visibly rotten deck, or joists with dark, crumbling ends.
- A covering that is cracked, blistered or worn across its whole surface, not just in one place.
- Repeated leaks in different places, each fixed and followed by another.
- A roof that holds standing water because it has sagged, with no fall to the outlet.
- Corrugated sheets that are cracked, mossy and brittle, with fixings that have rusted through.
- A pitched roof with many slipped tiles, perished battens or an underlay in tatters.
Any one of these is a warning, and several together are a verdict. The covering has a limited life, and a garage roof that has reached the end of it will cost more in patches than it saves. Our guide to garage roof options shows what you can put on instead.
Why the material matters
The same fault means different things on different coverings. A split in felt can be cut out and patched in an afternoon, while a split in an old EPDM sheet might point to a roof that has shrunk and is under strain. A cracked corrugated sheet is awkward: asbestos cement cannot be patched and must not be broken up, so even a small crack may mean that the roof has to be dealt with under the asbestos rules. Our guide on asbestos garage roof removal explains what that involves, and the answer on why a garage roof leaks goes through the common causes.
Roof sheets made of bitumen-impregnated board or thin metal sag, rust or lose their coating as they age. Felt blisters and splits. A GRP roof cracks where the deck moves. A tiled roof depends on the battens and underlay, which may be far more worn than the tiles above them. The repair question is always whether the material is still capable of doing its job.
What a repair involves on each type of roof
Knowing what a proper repair looks like helps you judge whether a quote is realistic.
Felt
A split or blister is cut out, the area is dried and cleaned, and a patch of new felt is bonded or torched over it, extending well beyond the damage and lapped so water runs over, not under, the edges. Lifted laps are re-bonded. A thin coat of bitumen paint on a failing felt is a stopgap, not a repair.
EPDM and GRP
EPDM is repaired with a patch of the same rubber, bonded with the correct adhesive or tape after cleaning and priming. GRP is repaired by grinding back the damaged area, laying new matting and resin, and refinishing the topcoat. Both depend on the area being clean and dry, which is why a repair done in the rain rarely lasts.
Sheets and tiles
Metal and fibre-free sheets can have individual sheets replaced, fixings renewed and sealing washers refitted. Tiles and slates are re-seated or swapped, and any damaged underlay or batten is replaced alongside. Asbestos cement sheets are different: they should not be cut, drilled or disturbed, so any work on them is planned under the asbestos rules.
Temporary measures while you decide
If water is coming in now, limit the damage first. Move stored items away from the drip and cover what cannot move. Put a bucket under the leak and, if the ceiling is bulging with water, make a small hole at its lowest point to let it drain safely into the bucket. Keep clear of any electrics that are wet. A tarpaulin pinned over a pitched roof, or a temporary patch on a flat one, can hold a leak until the weather allows a proper repair, though going on a wet roof is dangerous and is best left to someone equipped. If the leak is serious, ring us: emergency calls go to the front of the queue, and stopping the water comes before any longer-term plan. Keep a record of what you did and when, with dated photographs of the damage, since the same record helps with any insurance claim and tells a roofer how fast the problem is developing.
The cost of waiting
Putting off a necessary replacement is not free. Water that gets into a garage roof soaks the timbers, rusts fixings and damages what is stored below. A deck that could have been saved by an earlier re-cover has to be replaced, adding to the bill. Condensation and leaks together create mould and rot, and a leak above a shared wall can affect the house. Meanwhile each patch has a cost, and several patches in a year can add up to a substantial part of a replacement. The sensible approach is to price both routes and compare them honestly.
For a view of what replacement might cost, see our garage roof replacement cost guide. Published cost guides give wide ranges. Your fixed quote follows the survey.
Overlay: a third option
Between a repair and a full strip sits the overlay, a new covering laid over the old one. It saves the cost of removal and disposal, and it can be a reasonable choice when the old covering is firmly fixed, the deck is dry and no moisture is trapped. It is not suitable if the deck is wet, if the old roof is sagging, or if the extra weight is a concern. Asbestos cement sheets can sometimes be overlaid, but only on a frame strong enough and with no other asbestos materials present. The overlay decision is a technical one, and a survey is the only way to settle it.
Questions to ask before deciding
When you have a quote for a repair or a replacement, a few questions test whether it is sound. Ask what is wrong with the roof and where, and ask to see photographs. Ask what the deck and frame are like and how that was checked. Ask how long a repair should last and what would cause it to fail. Ask what a replacement would involve if the repair does not hold. A contractor who cannot answer these is guessing. A contractor who recommends replacement but cannot show you a rotten deck, or one who recommends a patch on a roof that is plainly finished, deserves a second opinion.
What our survey covers
On a garage roof we look at the covering, the deck or sheets, the frame, the edges, the gutters and the connection to the house. Where there is a way in, we look from below. We take photographs of faults, and of sound areas for comparison. If the roof is corrugated and old, we raise the question of asbestos and arrange a sample where needed. Then we explain what we found in plain terms, say whether the answer is a repair, an overlay or a replacement, and put the price in writing.
Where a patch will do the job we price a patch, and a roof with time in hand is told as much. If it is finished, we say that too, and show you why. A replacement carries a written guarantee for ten years on our workmanship. Call 01256 213956 to book a visit, or read about our garage roof replacement in Basingstoke service.
