Thetford Roofers surveys, repairs, and replaces flat roofs for homeowners in Brandon, working on extensions, garages, and bay windows with felt and EPDM systems.
Flat roofs on domestic extensions and garages have a reputation for causing problems, but most failures come down to a short list of known causes. Understanding what those causes are makes it easier to spot trouble early, ask the right questions when a roofer visits, and make a confident decision about repair versus replacement. If your flat roof in Brandon is showing warning signs, a proper survey is the right place to start.
We cover Brandon and the surrounding area, including Thetford, Mundford, Elveden, Barnham, Kilverstone, Croxton, Brettenham, and East Wretham. Call us to arrange a survey and we will give you a clear picture of what is happening on your roof before any work is agreed.
A flat roof inspection covers three key areas: the falls and drainage outlets, the perimeter edges, and the junctions where the roof meets a vertical wall. Each one is a recognised failure point, and a thorough survey looks at all three rather than just the area where a leak has appeared.
Falls and outlets. A flat roof needs a slight slope - typically a minimum of 1:80 - to carry water to the outlet. Where the fall has settled out of level, or where the outlet is blocked by debris, water sits on the surface. Standing water weakens felt membranes over time and puts sustained load on the roof deck.
Perimeter edges. The edge of a flat roof is where the membrane terminates. On a felt roof, a timber fascia and metal drip edge finish the detail. When the timber rots or the trim lifts, water tracks back under the felt and into the structure. On EPDM roofs, the edge is bonded and fixed, but it still needs checking where it meets adjacent structure.
Wall upstands and flashings. Where the roof meets a wall, the membrane is dressed up the face of the wall and covered by a flashing. This is one of the most common leak points on any flat roof. When the mortar holding the flashing fails or the lead lifts, water enters at the junction and tracks across the deck before appearing inside - often some distance from the actual entry point.
For domestic flat roofs, the two most practical systems are built-up bitumen felt and EPDM rubber membrane. Both perform well when properly installed. The right choice depends on the size and shape of the roof, the complexity of any detailing, and what is happening to the existing deck.
Built-up felt uses multiple layers of bitumen-impregnated felt, usually torch-bonded, over an insulated deck. A three-layer system with a mineral-finish cap sheet is the accepted standard for domestic work. Typical installed cost runs from around £40-£60 per square metre, varying with access, deck condition, and edge detailing.
EPDM is a single-ply rubber membrane bonded directly to the deck. It handles movement in the structure well and is a reliable choice for roofs with rooflights, multiple upstands, or a complex shape. Installed, EPDM typically costs £60-£90 per square metre. Both figures are general market ranges - an accurate price depends on the actual dimensions and condition of your roof.
Before any new membrane goes on, the deck must be sound and dry. Laying new waterproofing over a wet or rotten deck shortens the life of the new roof and can trap moisture that causes further decay from below.
Most flat roof failures give warning before they become serious. Catching a problem at the early stage usually means a repair rather than a full replacement, and it always means less damage to the structure and the rooms below. Here are the signs to watch for and what each one typically means.
This is the sign most homeowners notice first. A damp patch directly below a flat roof almost always means water is getting through somewhere above - but the wet area on the ceiling is not always directly below the entry point. Water follows the fall of the deck and travels along joists before dripping through, so the source of the leak may be a metre or more away from where the damage appears. A roofer needs to trace the water path from above, not just patch the area above the stain.
Fresh staining after rain confirms an active leak. Old brown staining that is dry may mean a previous repair was done but the underlying problem was not fully resolved, or that a repair has failed again.
Blisters form when moisture or air is trapped between the layers of a built-up felt roof. They appear as raised bubbles in the surface, sometimes several centimetres across. A blister that is intact is not immediately letting water in, but it is a sign that the felt layers are delaminating and that the membrane is under stress. Once a blister splits - usually from foot traffic, thermal movement, or frost - it becomes an open crack that lets water straight through.
Multiple blisters across a roof surface indicate a more general failure of the felt system rather than an isolated spot repair, and often point towards replacement being more practical than patching.
Felt becomes brittle with age. Thermal cycling - the expansion and contraction of the deck and membrane through hot summers and cold winters - eventually causes cracks to open, particularly at joints, around upstands, and along the perimeter edge. A single crack can be repaired, but widespread cracking is a sign that the felt has reached the end of its useful life.
Splits are also caused by structural movement. If the deck below has softened or deflected, the membrane above is asked to stretch beyond what it can accommodate, and it splits. In that case, the deck itself needs attention before a new membrane will stay intact.
Some temporary ponding in very heavy rain is normal. Water that is still sitting on the roof two days after rain stopped is not. Persistent standing water accelerates the breakdown of any membrane and adds weight to the deck. It also indicates that either the fall has failed - sometimes because the deck has deflected at the centre - or that the drainage outlet is restricted.
On EPDM roofs, standing water is less immediately destructive than on felt, but it still puts load on the deck and encourages moss and algae growth that can eventually compromise the membrane adhesion at the edges.
Flashings at wall junctions are often the first thing to fail on an ageing flat roof. Lead flashings can lift as the lead expands and contracts, eventually pulling out of the mortar joint that holds them. Aluminium or fibrous flashings degrade faster than lead and may crack rather than lift. In either case, a gap between the flashing and the wall is an open invitation for water.
This is a common point of failure on the back of extensions, where the roof meets the rear wall of the original house. Repointing the mortar joint above the flashing is not enough if the flashing itself has pulled away - it needs to be re-dressed and secured before the mortar goes back.
If you can access the roof surface safely (without walking on a surface that may not support you), a soft or springy feel underfoot indicates that the deck below has taken on moisture and the timber is no longer structurally sound. Wet decks look fine from above but compress under load. This kind of damage does not repair itself - the affected sections of deck need to be cut out and replaced before a new membrane is worth installing.
On older properties, the deck may be built from the original flat-roof boarding with no rigid insulation. These roofs often have poor thermal performance as well as structural issues, and replacement is a sensible opportunity to bring the insulation up to a reasonable standard at the same time.
Moss on a flat roof is a warning sign rather than a direct cause of failure, but it deserves attention. Moss holds moisture against the surface, which accelerates felt degradation. Roots from moss and other vegetation can also work their way into splits in the membrane, widening them. If moss is growing on your flat roof, clear it with a biocide rather than by scraping, and check the surface carefully for any underlying damage it may have been concealing.
A repair makes sense when the damage is genuinely localised - a single split, a lifted flashing, a blocked outlet. If the rest of the membrane is sound and the deck is dry, a targeted repair done properly can extend the roof's life by several years.
Replacement is the right choice when the felt is delaminating across a wide area, when multiple blisters have opened or are likely to, when the deck is wet in more than one place, or when a roof has already had several patches that have not held. At that point, further repairs become more expensive cumulatively than a single replacement, and the result is more reliable.
Flat roofs in this part of the country typically last 15-25 years depending on the system, the installation quality, and how well the drainage has been maintained. An EPDM roof installed on a sound deck, with properly finished upstands and a clear outlet, can reach the top end of that range without major intervention.
If you have spotted any of the warning signs above on your flat roof in Brandon, call Thetford Roofers to arrange a survey. We will look at the falls, the edges, and the junctions properly and give you a straight answer on whether a repair or a replacement is the right course of action. The sooner a problem is assessed, the more options you have.
No obligation · We usually respond within 2 hours
Storm damage, active leak, damaged ridge - we aim to be on-site within 24 hours.
