Cambridge Roofers installs and repairs flat roofs for homeowners in Cottenham, and we want every roof we fit to still be performing well a decade from now - which means knowing how to look after it.
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A flat roof installed correctly with a good-quality EPDM rubber or torch-on felt system should give you many years of trouble-free performance. The ones that fail early almost always do so for the same reasons: debris blocks the drainage, a minor fault is left unchecked until water has worked through the deck, or someone goes up on the roof without knowing what they are doing and damages the membrane. Most of that is preventable.
This page covers the aftercare and maintenance steps that keep a flat roof in good condition and avoid the expense of an early repair or replacement. The same principles apply whether you have a new installation on a Cottenham extension or a roof that has been there for several years.
The two systems we fit on residential properties are EPDM rubber membrane and torch-on felt. EPDM is a single-ply rubber sheet bonded or mechanically fixed to the deck. It is flexible, tolerates frost and UV exposure, and a correctly installed EPDM roof can last 25 years or more. Torch-on felt is a multi-layer bitumen system, heat-welded during installation. Both are proven systems - which one suits your property depends on the roof's size, shape, access, and what already exists.
Maintenance requirements differ slightly between the two, but the core tasks are the same: keep the surface clear, keep the drainage clear, and inspect the edges and flashings at least once a year.
The single most important maintenance task on a flat roof is keeping the outlet or outlets clear. Because a flat roof has almost no gradient, even a small amount of leaf debris or silt can block an outlet and cause water to pond. Ponding water adds weight to the structure and finds any weakness in the membrane or its detailing. On a domestic extension or garage roof, the outlet is usually a simple internal drain or an external scupper at the edge. Check it two or three times a year, particularly in autumn when leaf fall is at its heaviest.
If you have trees overhanging or close to your roof, this becomes more important. Moss and algae also accumulate around outlets over time and can slow drainage without fully blocking it. A bucket of water poured onto the roof surface will quickly show you whether the outlet is flowing freely.
Leaves, twigs, and general debris sitting on a flat roof hold moisture against the membrane. Over time, that sustained dampness can degrade the surface of a felt roof and encourage moss growth that eventually lifts the membrane at its edges. On an EPDM roof, debris is less of a chemical threat but can still obscure developing problems during your inspections.
Clearing the surface once or twice a year - ideally in late autumn after the leaves have fallen and again in spring - takes 20 minutes and is one of the most cost-effective maintenance habits you can have. Use a soft brush rather than a pressure washer; high-pressure water can lift the edges of the membrane or force water under flashings.
The edges of a flat roof - where the membrane meets the fascia board, turns up against a wall, or wraps around a parapet - are where problems begin. The membrane in the middle of the roof rarely fails. Water gets in at the junctions. A simple annual inspection from a safe position, or from a ladder at the edge, should check the following.
Catching a failed flashing early is a modest repair cost. Leaving it for another winter means water has worked into the deck and the repair becomes a much larger job.
Moss on a flat roof is more than cosmetic. Its roots work under the surface of felt systems and can lift the edges of EPDM membrane where it is bonded at the perimeter. A biocidal treatment applied to a clean, dry surface kills moss and inhibits regrowth. Products are available at builders' merchants and are safe for use on both felt and rubber membranes. Apply according to the manufacturer's instructions and do not wash the residue into water butts or garden ponds.
On a felt roof, heavy moss growth can also hold moisture and accelerate the drying out of the bitumen surface. If the surface feels brittle or is showing fine crazing when the moss is cleared, that is a sign the felt system is reaching the end of its life and a replacement survey is worth arranging.
A full EPDM flat roof installation in this area typically costs between £70 and £120 per square metre, depending on deck condition, access, and the complexity of the edging and flashings. A standard garage roof of around 15 square metres might be in the range of £1,200 to £2,000. A larger extension roof of 40 square metres could be £3,000 to £5,000 or more. These figures assume the deck is in reasonable condition; significant deck replacement adds cost.
Targeted repairs - a failed flashing, a single membrane split - are a different scale entirely, typically a few hundred pounds. The point of good aftercare is to keep problems at that scale rather than letting them develop into a full replacement job prematurely.
There is no benefit to waiting if you see any of the following: a damp patch on the ceiling below the roof, visible standing water that has not cleared within 48 hours of rain, a section of the edge trim or flashing that has clearly lifted, or any soft or springy area when you walk across the roof surface. These are signs that water is already in a place it should not be, and time is working against you.
A flat roof that has been leaking for weeks or months will have wet deck boards beneath the membrane. Wet timber swells, moves, and rots - and when it does, the repair cost rises sharply because the deck itself needs replacing before any new membrane can go on.
For anyone considering a new flat roof in Cottenham, the process starts with stripping back the existing covering to inspect the deck. Any damaged boards are replaced. The fall is checked and corrected if needed - a minimum 1:80 gradient is required for reliable drainage. Edge trim is fitted, the membrane is laid and bonded, and the upstands and flashings are detailed. The finished roof is inspected and cleared before we leave. On a typical garage roof, the work takes one to two days.
Whether you want a new flat roof installed, an existing one repaired, or simply an honest assessment of what condition yours is in, call Cambridge Roofers to arrange a survey. We cover Cottenham and the surrounding Cambridge area and will give you a clear picture before any work is agreed.
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Call any time. Calls are answered day and night and passed straight to our roofers.
