If you have a flat roof on your extension, garage or outbuilding in Elmswell and it is giving you trouble, here is exactly what the job looks like from the moment we arrive to the moment we leave.
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A flat roof is not truly flat. It is laid to a very slight fall, typically around 1 in 80, so rainwater drains towards an outlet rather than pooling on the surface. When that fall is lost, or when the surface covering fails, water sits still on the deck and works its way in. That is the root cause of the vast majority of flat roof problems.
Three main systems are used on residential flat roofs: built-up felt (layers of bitumen felt bonded together), EPDM rubber (a single-ply synthetic rubber membrane), and torch-on felt (a reinforced bitumen membrane applied with heat). Each has its place depending on the roof area, budget and what is already there. A good flat roofing job starts by matching the system to the situation, not fitting the cheapest option available.
Before any work is quoted or priced, the roof needs a proper inspection. That means getting up on it, not just looking from the ground. From ground level you can see obvious splits or lifted edges, but you cannot see where the deck boards are soft, where the falls have gone wrong, or whether the existing felt has been overlaid so many times that the whole system is sitting proud of the upstands.
During an inspection, a few key things are checked: the condition of the decking underneath, the state of any upstands and abutments where the roof meets a wall, the outlets and any rainwater goods, and whether any previous repairs have been done properly or just patched over. A flat roof that has had repeated temporary patches often has underlying deck damage that only becomes clear when you strip it back.
If you are in Elmswell and having a flat roof inspected, ask specifically whether the inspector got on to the roof surface and checked the deck for softness underfoot. A quote based only on a ground-level look is not a reliable quote.
Once work starts, the first task is removing the existing covering. On a garage or extension roof, this often reveals the true condition of the timber deck. OSB and plywood both absorb moisture over time, particularly around outlets and at the edges. Soft or delaminated boards must be replaced before any new membrane goes down, because a new covering laid over a failing deck will fail too, usually within a few years.
Flat roofs on older extensions sometimes have multiple layers of felt laid on top of each other. Building regulations generally allow no more than two layers before a full strip is required, partly because of the added weight and partly because trapping the layers seals in moisture. If you are quoted for a straightforward overlay on a roof that already has two or more layers, that is worth questioning.
Any defective firring pieces, the tapered battens that create the fall, are also replaced at this stage. If the original roof was built without adequate falls, now is the time to correct that. Adding firring correctly is a small additional cost compared to the long-term consequence of a dead-flat roof.
With the old covering stripped and any damaged decking replaced, the surface needs to be clean, dry and secure. Any exposed nail heads are punched down. Joins between deck boards are checked. If there are gaps or movement between boards, these are addressed before any membrane goes on, because movement in the deck will eventually stress and split whatever is on top of it.
For EPDM rubber installations, the deck is cleaned and a bonding adhesive is applied. For torch-on felt, the surface may receive an underlay first, depending on the system being used. For built-up felt, a base layer is mechanically fixed or bonded before the cap sheet goes on. Each method has its own preparation requirements, and skipping or rushing any of them is where problems start.
EPDM rubber is supplied in large sheets and is bonded to the deck in sections, with joins made using factory-specified tape and bonding agent. Done correctly, the join is as strong as the sheet itself. The membrane is turned up at all edges and bonded to the upstands, then trimmed to a neat finish. EPDM is a material that has been widely used in the UK for decades. It handles roof movement well and does not become brittle in cold weather the way older felt products can.
Torch-on felt is applied in strips using a gas torch to heat the underside of the membrane as it is rolled out. The heat creates a bond between the felt and the surface beneath. Cap sheet layers include a mineral finish that protects against UV. The overlaps between strips are critical: they need to be fully fused with no voids, because any cold join is a potential entry point for water.
Built-up felt systems use multiple layers, each bonded to the one below. They have been the standard approach for decades and, installed properly on a sound deck, perform well. The main limitation is that felt becomes more brittle as it ages, so the surface layer eventually cracks under thermal movement. An old built-up felt roof showing surface cracking is not necessarily at the end of its life if the bond to the deck is still sound and the cracks are shallow, but it does need attention.
The details are where flat roofs fail most often. An upstand is where the roof covering turns up against a wall, parapet or other vertical surface. It needs to be taken up to a minimum height, typically 150mm above the finished roof level, and sealed or counter-flashed into the brickwork above. If it is not taken up high enough, or if the lead flashing above it has failed, water will track behind the membrane and into the wall or ceiling below.
Drip edges, also called metal trim or edge trim, are fixed at the perimeter of the roof where it overhangs a fascia or wall. These direct water cleanly off the roof surface and into the gutter. If they are missing or poorly fitted, water runs back under the edge and rots the fascia and deck.
Outlets and downpipes are checked and cleared. If the outlet collar is not properly bonded into the membrane, that joint will eventually let water in. On a garage roof with a single outlet, blockage is also a risk, so leaf guards are worth considering where trees are nearby.
A properly finished flat roof looks tidy. The membrane lies flat without bubbles or wrinkles. Edge trims are straight and firmly fixed. Upstands are neatly turned and dressed. Lead or aluminium flashings are properly pointed into the brickwork above. The outlet is clear.
At the end of the job, all off-cuts, old felt and broken deck boards should be removed from site. Old felt goes to a skip or licensed waste facility and is not left for you to deal with. The area around the roof, gutters included, should be left clear.
Before leaving, the completed roof should be walked and checked. Any bubbles in a freshly laid EPDM or torch-on sheet, any loose edge trim, any suspect joins should be found and addressed at this point, not discovered by the next downpour.
This is the question most homeowners face. A repair makes sense when the deck is sound, the existing covering is largely intact and the failure is limited to a specific area, such as a split at a join or a lifted upstand. A targeted repair on a roof in otherwise good condition can add years of life for a relatively small cost.
Replacement is the right call when the deck has widespread moisture damage, when the covering is cracked and lifting across the whole surface, or when the roof has already been repaired multiple times in the same areas. Repeated patches on a flat roof are a sign that the covering has reached the end of its serviceable life. At that point, another patch is spending money on something that will need doing again within a year or two.
As a rough guide, EPDM rubber membranes typically last 20 years or more when installed correctly. Torch-on felt cap sheets typically last 15-20 years depending on the quality of the product and the exposure of the roof. Standard built-up felt has a shorter lifespan, often 10-15 years before the surface layer shows significant deterioration. These are typical industry figures, not promises for any specific job.
Flat roofing costs in the UK currently range from around £70 to £120 per square metre for a straightforward replacement, depending on the system chosen and the condition of the existing deck. EPDM tends to sit in the middle to upper end of that range due to material costs, but its longevity means it often represents better value over time. Torch-on felt is generally at the lower to middle end. Built-up felt can be cheaper still for a simple garage roof.
Deck replacement adds cost. A new 18mm OSB deck over a typical garage roof area of around 20-30 square metres adds several hundred pounds to the overall price, depending on how much board needs replacing. Upstand repairs, new lead flashings and new guttering are all priced separately if they form part of the job.
A repair to a localised area, such as a single failed join or a lifted upstand, might cost from £150 to £400 depending on access and the extent of work needed. Any quote that does not specify what is and is not included is worth querying before you agree to it.
Whether you are in Elmswell or a neighbouring village, the same questions apply when getting a flat roofing quote. Did the person quoting physically get on the roof? What system are they proposing and why? Will the deck be inspected before the new covering goes down? What happens to the waste? Who is responsible for any damage found once stripping starts?
A roofer who can answer these questions clearly and specifically is more likely to do the job properly than one who gives vague answers or a quote without getting on the roof first.
We carry out flat roofing work in Elmswell and the surrounding area, including jobs in nearby Diss and other villages across this part of Suffolk and south Norfolk. If you have a flat roof on a garage, extension, porch or outbuilding that needs attention, call us to arrange a proper roof inspection and a straightforward quote for the work.
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Call any time. Calls are answered day and night and passed straight to our roofers.
