Diss Roofers installs and repairs flat roofs on extensions, garages and outbuildings for homeowners in Long Stratton and the surrounding villages.
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A flat roof is not truly flat. It is laid to a slight fall, typically around 1:40 to 1:80, so rainwater drains towards outlets rather than pooling. Getting that fall right from the start is the single most important factor in whether a flat roof performs well over its lifetime. Poor drainage causes standing water, and standing water causes every kind of trouble: membrane degradation, timber deck rot, leaks into the room below.
Flat roofs are common on single-storey extensions, kitchen and bathroom additions, garages, outbuildings and flat-roofed dormer sections. Each situation is slightly different in terms of the deck construction, the insulation requirements and the membrane system best suited to it. A good installation takes all of that into account before a single sheet is cut.
Three systems account for most residential flat roofing work in the UK today: built-up felt, EPDM rubber and modern torch-on felt. Each has real advantages and real limitations.
Built-up felt uses multiple layers of bitumen-based felt bonded together with hot bitumen or cold adhesive. It is the system most people associate with older flat roofs and, when correctly installed with at least three layers, it performs reliably. The limitation is that older single or double-layer felt installations were not built to last, which is why so many pre-1990 flat roofs leak. A built-up felt system installed to current standards typically performs for 15-20 years before it needs attention.
EPDM rubber is a single-ply membrane made from synthetic rubber. It is highly flexible, handles temperature changes without cracking, and can be laid in large sheets with very few seams. Fewer seams means fewer potential failure points. EPDM is particularly well suited to roofs with unusual shapes or penetrations such as roof lights, pipes and vents. A correctly installed EPDM membrane can last 25-30 years or more before replacement is needed.
Torch-on felt (also called modified bitumen or SBS felt) is a heavy-duty felt system applied with a gas torch. It bonds directly to the deck and, when installed as a two-layer system, gives a tough and durable finish. Torch-on is a common choice for straightforward flat roof replacements where cost is a consideration alongside longevity.
This is where most homeowners in Long Stratton get caught out, not by the roofing itself but by choosing the wrong person to do it. A flat roof that leaks within three years of being installed is almost always a workmanship problem, not a materials problem. The materials available today are genuinely good. The question is whether the person installing them knows exactly what they are doing.
Here is a set of plain, practical questions to ask any contractor before you agree to the work. A contractor who cannot answer these clearly, or who seems irritated by them, is telling you something important.
Before any membrane goes down, the structural deck underneath must be sound. Older flat roofs use timber joists and boarding, or a layer of chipboard. A common problem is that moisture from a leaking roof has rotted sections of the deck from the inside. If a contractor proposes to lay a new membrane straight over an old, potentially soft deck without checking it thoroughly, the new roof will not perform. Ask specifically: "Will you inspect and probe the deck before stripping? What happens if you find rot?" You want a clear answer about what rot replacement costs and who makes the call.
The deck should also be rigid enough for the system being installed. EPDM can tolerate minor deflection in a deck better than a rigid torch-on felt can, but neither should be laid over a deck that moves noticeably underfoot. Any decent contractor will tell you this unprompted.
If the existing roof structure gives you a fall of nearly zero, the membrane alone will not solve the problem. Some contractors use tapered insulation boards to create fall where the structure cannot provide it. Others will tell you the existing pitch is fine when it is not. Ask: "What is the existing fall, and is it adequate? If not, how will you address it?" Tapered insulation adds cost but it is sometimes the right answer.
Any flat roof on a habitable space, meaning a room you actually use, is subject to Part L of the Building Regulations, which sets minimum thermal performance standards. If you are replacing a flat roof on a kitchen extension or a living room, the new roof must meet current U-value requirements. The relevant U-value for a flat roof is currently 0.18 W/m2K or better. This almost always means adding or upgrading insulation at the same time as the membrane.
Ask the contractor whether the job requires building regulations approval, whether they will handle the application, and what insulation specification they are proposing. A contractor who says building regulations do not apply to a re-roof of a habitable space without giving a specific reason why they do not is worth questioning further.
Outlets, gutters and downpipes are not an afterthought. Ask where the water is going and how. On an extension, you may be draining into a guttered edge, or through an internal outlet. Internal outlets need attention because blockages cause water to back up across the whole roof surface. Ask whether the contractor will inspect and clear outlets as part of the job, and whether the falls direct water reliably towards them rather than away from them.
Flat roofing quotes vary enormously because the scope of work varies enormously. A quote that strips the old roof, replaces the deck where needed, installs tapered insulation, applies a full EPDM system, dresses all upstands and trims, and takes away all waste is a different proposition to a quote that lays a new layer of felt over an old one and leaves the skip hire to you. Both might look similar on a price sheet if you do not know what to ask.
Typical flat roofing costs in the UK currently run from around £70 to £120 per square metre for a torch-on felt system, £90 to £130 per square metre for EPDM rubber, and £80 to £120 per square metre for a built-up felt system. These figures cover materials and labour on a standard residential job. Deck replacement, new roof lights, insulation upgrades and complex drainage arrangements will add to the total. A small single garage roof of around 15-20 square metres might cost £1,200 to £2,500 in total. A large kitchen extension roof of 30-40 square metres might range from £3,000 to £6,000 depending on the system and any additional work required.
Ask the contractor to break the quote into its component parts: strip and dispose of old materials, deck inspection and any replacement, insulation, membrane system, edge trims and flashings, drainage work. If they cannot or will not do this, you cannot compare quotes fairly.
The edge of a flat roof is where failures most often begin. Where the membrane meets a wall, a parapet, a dormer cheek or a roof light frame, it must be dressed up and sealed against the adjoining surface. These upstands should be a minimum of 150mm high. Where there is a step flashing or a lead or aluminium trim, it must be properly fixed and sealed. Ask to see examples of how the contractor handles these details. Photographs on a phone are fine. A contractor who dismisses the question has probably cut corners on these details before.
A flat roof on a garage is not the same as a flat roof on a two-storey extension. Ask whether the contractor has done jobs similar to yours and whether you can speak to those customers or see the work. Homeowners in Long Stratton and nearby villages like Diss should be within easy reach for any genuinely local contractor. If references are not forthcoming, that is worth noting.
Old felt, insulation and roofing boards need to be disposed of properly. Fly-tipped roofing waste is a criminal offence and the liability can fall on the homeowner as well as the contractor. Ask specifically whether skip hire or licensed waste disposal is included in the price, and ask for the name of the waste carrier if you want to check. This is not an unreasonable question and any contractor who has been in business properly for any length of time will have a straightforward answer.
When the work is complete, you should be able to see a clean, uniform membrane surface with no bubbles, ridges or obvious repair patches. All upstands should be dressed neatly and secured. Edge trims should be fixed at regular intervals and run true. Any roof lights or penetrations should have neat collars or flashings that bed tight against the frame. The drainage outlets should be clear and water should visibly track towards them when you pour water onto the surface, not sit in hollows.
The falls are harder to check by eye but you can ask for a simple test after a rain shower. If standing water persists more than 48 hours after the last rain, you have a drainage problem that needs addressing before you sign anything off.
Flat roofs benefit from an inspection every one to two years. This is straightforward and does not need to be expensive. The inspection should check for any membrane splits or blistering, check that upstands and flashings are still tight, and make sure all outlets and gutters are clear. Catching a small blister or a lifting flashing early costs far less than dealing with the water damage caused by leaving it.
Moss and debris accumulate on flat roofs more readily than on pitched ones because they drain more slowly. Keeping the surface clear of leaf litter and checking that outlets are not blocked is something most homeowners can do safely from a ladder at gutter level, though anything that involves walking on the membrane itself is best left to a roofer who knows how to do it without causing damage.
If you have a flat roof on an extension, garage or outbuilding in Long Stratton that is leaking, blistering or approaching the end of its life, call us for a roof survey. We will tell you honestly whether it needs a repair or a full replacement, explain which system suits your situation, and give you a clear breakdown of what the work involves and what it will cost.
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Call any time. Calls are answered day and night and passed straight to our roofers.
