Key points
- Check a flat roof twice a year, in late autumn and spring, and after big storms.
- Do every check from a window, the ground or a ladder at the eaves if it is safe; never climb onto the roof.
- Keeping outlets and gutters clear prevents more flat roof problems than anything else.
- Never walk on, pressure wash or sealant-patch a flat roof; a reflective coating on sound felt is maintenance, not a repair.
How often should a flat roof be checked?
Twice a year is the usual advice: once in late autumn after the leaves have fallen, and once in spring after the winter weather. It is also worth a look after a big storm or long, heavy rain.
The autumn check matters most, because blocked outlets and gutters are the commonest cause of water backing up over a roof's details in winter. Roofs under trees, near the coast or on exposed sites may need checking more often, and commercial roofs and blocks of flats are often put on a planned inspection by a roofer, typically once or twice a year.
How can you check a flat roof safely?
From a window that overlooks the roof, from the ground, or from a ladder at the eaves only if it is safe to do so. Do not climb onto the roof. Flat roofs should be treated as fragile until a competent person confirms otherwise, and many older garage and extension decks will not take a person's weight between the joists.
If you use a ladder to look along the gutter or edge, keep it on firm, level ground, tie it or have someone foot it, keep three points of contact, and never step off it onto the roof. If the only view means leaning out or working at height without protection, leave it to a roofer.
A clear view from an upstairs window or the ground is often enough to spot the things that matter. Jot down what you saw and the date, so you have something to compare against next time.
What should you look for on each check?
Look for anything that stops water draining, and anything that has moved, split or worn since last time. A simple checklist:
| Look at | What to look for | Usually means |
|---|---|---|
| Outlets and gutters | Leaves, moss, silt, plants growing | Clearing needed before winter |
| Surface after rain | Water still there two days later | Drainage or falls problem |
| Felt surface | Bare black patches where chippings have gone | Ageing; may suit a reflective coating |
| Membrane | Blisters, cracks, crazing, split laps | Repair or survey needed |
| Walls and upstands | Lifted flashings, cracked pointing or render | Water may be getting behind |
| Edges | Loose, split or missing drip trims | Wind and rain getting under the edge |
| Inside | Stains, damp or mould on the ceiling below | Leak or condensation |
Anything in the last four rows is worth a roofer's inspection.
How do you keep outlets and gutters clear?
Clear them before winter and again in spring, and more often under trees. Gutters along the edge of a garage or extension roof can usually be cleared from a ladder at the eaves, if it is safe, scooping out debris without reaching over or onto the roof.
Outlets in the middle of a roof, or at a parapet, can only be reached by going onto it, so ask a roofer. A wire or plastic leaf guard over an outlet, checked at each visit, cuts down blockages. Leaf guards on gutters help too, but they still need clearing.
A blocked outlet does more than leave a puddle: water can rise above the height of laps and upstands, which are not designed to be under water. Our edges, outlets and drainage page covers outlets that keep blocking or are in the wrong place.
What should be done about moss and debris?
Have it removed gently and regularly, before it builds up. Moss holds water against the surface, its roots work into laps and cracks, and loose clumps wash into outlets. Leaves and twigs do the same.
A roofer will normally remove moss by hand or with a soft brush, sweep debris clear and, where the system allows, apply a moss treatment that is compatible with the membrane. Some treatments and household chemicals can harm bitumen, EPDM or single-ply, so check with the roofer or the system's manufacturer before anything is applied. Cutting back overhanging branches reduces both leaf fall and shade, which helps the roof dry out.
What happens when a felt roof loses its chippings?
The bitumen underneath is left exposed to sunlight, one of the main things that ages felt. Mineral chippings or a mineral-surfaced cap sheet protect the bitumen from UV and reflect some heat; once they wash or wear away, the exposed felt becomes brittle and cracks sooner.
Loose chippings also collect in gutters and outlets, so a roof shedding chippings needs its drainage checking more often.
On a felt roof that is otherwise sound and dry, a solar reflective coating applied by a roofer can restore that protection and reduce surface temperature. It needs to be a product compatible with bitumen, on a clean, dry, sound surface. It is maintenance, not a repair: it will not seal a split lap or fix a wet deck. Where the felt is widely cracked or blistered, the overlay or strip guide and repair or replace guide are the next read.
What should you never do to a flat roof?
Do not walk on it, pressure wash it or patch it with sealant. Each is common, and each causes damage.
- Walking on it. Apart from the risk of falling or going through a fragile deck, foot traffic punctures membranes, crushes insulation and dislodges chippings. Even roofers use crawl boards or walkways on roofs not designed for traffic.
- Pressure washing. A jet can strip chippings, lift laps, force water under the membrane and erode the surface of felt, coatings and EPDM. Leave cleaning to a soft brush and low-pressure water.
- Sealant or bitumen paint patches. A tube of sealant over a crack rarely bonds properly, can trap water and makes a proper repair harder. Incompatible products can also void a guarantee; see the flat roof guarantees guide.
- Fixing things through it. Satellite dishes, aerials and solar brackets screwed through the membrane are a common source of leaks. Ask a roofer to form a proper detail.
- Using it as a terrace. Furniture and pots need a roof designed for them.
How does maintenance differ between EPDM, GRP and felt?
The routine is the same for all of them, keeping drainage clear and checking details, but each system has its own weak points to watch.
- EPDM: check edge trims, seams and the bond at upstands; avoid solvents and oil-based products, which can affect rubber.
- GRP: look for hairline cracks at joints between boards, trims and corners, and wear on the top coat.
- Torch-on felt: watch for lost chippings, blisters and split laps, especially at the edges.
- Liquid-applied roofs: check for thin or worn areas and follow the manufacturer's recoat guidance.
Good maintenance is one of the reasons roofs reach the upper end of their expected life; the lifespan guide gives ranges by system.
How much does flat roof maintenance cost?
An inspection visit by a roofer is a guide £150–£300, and routine clearing and checks usually cost far less than the repairs they prevent. Clearing outlets and checking details is often done during that visit, with any small repairs found quoted in writing before they are done. Typical small repairs, including VAT:
| Work | Guide price |
|---|---|
| Patch repair to the membrane | £150–£500 |
| Outlet repair | £120–£350 |
| Upstand or flashing repair | £250–£650 |
These are guide prices; the fixed price follows a look at the roof. For blocks and HMOs or commercial roofs, ask about planned inspections. Book through contact or see the cost guide.
More questions
Can I clean my flat roof with a pressure washer?
No. A pressure washer can strip chippings, lift laps and force water under the membrane. Moss and dirt should be removed gently by a roofer with a soft brush.
Is it safe to stand on my garage roof to clear it?
Do not assume so. Treat every flat roof as fragile until a competent person confirms otherwise, and clear gutters from a ladder at the eaves only if that is safe, leaving the roof itself to a roofer.
Does a reflective coating make an old felt roof last longer?
On a sound, dry felt roof that has lost its chippings, a compatible solar reflective coating can slow ageing by shielding the bitumen from sunlight. It will not fix cracks, split laps or a wet deck.
Do I need to maintain an EPDM or GRP roof?
Yes. They need less attention than felt, but outlets, gutters, edges and upstands still need checking twice a year, and debris still needs clearing.