Diss Roofers carries out flat roof repairs and full replacements for homeowners in Dickleburgh and the surrounding area.
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Flat roofs are used on extensions, garages, outbuildings and dormer sections. They are not genuinely flat but pitched very slightly, typically a fall of around 1:40 to 1:80, so rainwater tracks towards outlets rather than pooling across the surface. When that fall is correct and the membrane is sound, a flat roof performs well for many years with minimal attention. When either the fall or the membrane fails, water gets in quickly.
Most of the flat roof work done on homes today involves either repairing a section that has begun to fail or replacing an entire roof that has reached the end of its useful life. Deciding which option is right is not always straightforward, and the answer matters because choosing a repair when a replacement is needed wastes money, while replacing when a repair would have done the job wastes more. This page works through how to make that decision sensibly.
Built-up felt is the traditional system, used widely from the 1950s onwards. It uses multiple layers of bitumen felt bonded together. Older single and double-layer felt installations from before the 1990s were never designed to be long-lasting, and they are the source of most of the flat roof problems homeowners deal with today. A correctly installed modern built-up felt system, using three layers and high-quality materials, performs reliably for 15-20 years.
EPDM rubber is a single-ply synthetic rubber membrane. It is highly flexible, resistant to temperature extremes, and can be installed in large sheets that minimise the number of seams. Seams are where water finds its way in, so fewer seams means fewer risk points. EPDM suits roofs with roof lights, pipes and awkward shapes particularly well. A properly installed EPDM roof can last 25-30 years or longer before replacement is needed.
Torch-on modified bitumen felt is a heavy-duty felt applied with a gas torch. It bonds firmly to the deck and, laid as a two-layer system, gives a durable and cost-effective finish for straightforward replacement jobs. It is widely used for domestic flat roofing across the UK.
This is the central decision for anyone with a flat roof that is causing problems. Both answers can be right, depending on the condition of the existing roof. The wrong answer in either direction costs you money unnecessarily. Here is how to think through it.
A flat roof repair makes sense when the problem is localised and the rest of the membrane is still in good condition. Common problems that can be repaired rather than replaced include:
In each of these cases, the failure is at a specific point and the membrane elsewhere is performing. A targeted repair stops the water ingress without the cost and disruption of a full replacement.
A repair also makes financial sense when a roof is relatively new. If a felt roof is only five or six years old and has developed a single blister or a flashing problem, that is a workmanship or material defect at one location, not a sign that the whole roof needs to come off. Repair it properly and it should serve its full expected lifespan.
Typical repair costs for a residential flat roof in the UK range from around £150 to £600 for a straightforward localised repair, depending on the size of the affected area, the access required and the system involved. Flashing repairs and re-dressing can sit in a similar range. These are not small amounts, but they are substantially less than a full replacement.
A flat roof needs replacing rather than repairing when the underlying problem is widespread rather than localised. Signs that point towards replacement include:
The key principle is this: a repair fixes a point failure. It cannot fix a membrane that has reached the end of its material life. Patching a roof in five different places in the course of two years is a sign that the membrane as a whole is failing, not that you have been unlucky with five separate incidents. At that point, a repair is money spent on borrowed time.
When a flat roof is stripped back for replacement, the condition of the deck underneath often decides the final cost. Timber decks, whether joists and boarding or chipboard sheets, rot when water reaches them repeatedly. A deck that looked solid from below can be found to be soft or structurally compromised once the membrane comes off.
A common problem is that moisture sits between an old membrane and the deck for months or years before it finds its way through to the ceiling below. By the time the homeowner notices a leak, the deck may already have significant rot. Replacing sections of deck is standard practice and necessary work; it is not something a contractor should try to avoid or disguise. If you are getting quotes for a flat roof replacement, ask each contractor what happens if they find rot and how that additional cost is handled.
If your flat roof covers a habitable space, a full replacement triggers the requirement to meet current thermal performance standards under Part L of the Building Regulations. The relevant U-value for a flat roof is 0.18 W/m2K. Many older flat roofs, particularly those from the 1980s and 1990s, do not come close to this.
This is relevant to the repair-versus-replace decision because a repair does not trigger the same regulations. If your roof is borderline, the requirement to upgrade insulation during a replacement adds cost. In some situations, homeowners choose to repair rather than replace partly to avoid that additional expenditure, which is a legitimate choice if the existing membrane genuinely warrants repair. The key is making the decision honestly rather than choosing repair simply because the regulations are inconvenient.
Tapered insulation boards can be used during a replacement to improve both the thermal performance and the drainage fall simultaneously. This adds cost but may be the right solution where the existing structure gives insufficient fall.
A proper flat roof repair is not just applying a patch of mineral felt over a blister with a torch. Done correctly, it involves cutting out the damaged section, checking the deck underneath for any moisture damage or softness, replacing the deck if needed, applying compatible materials in layers that match the existing system, and sealing the edges of the repair so water cannot track underneath.
If the repair is at a flashing or upstand, the old flashing material must be removed, the wall surface prepared, and the new flashing properly dressed and fixed. A bead of sealant over a cracked flashing is a temporary measure, not a repair.
A full flat roof replacement typically involves stripping the entire existing membrane and disposing of the waste, probing and inspecting the deck and replacing any rotten sections, laying insulation to achieve the required thermal performance, installing the new membrane system with all upstands dressed correctly to at least 150mm, fitting edge trims and any new drainage outlets required, and checking falls once the work is complete.
Typical replacement costs for a residential flat roof in the UK currently range from around £70 to £130 per square metre depending on the system chosen and the condition of the existing deck. A standard garage roof of around 15-20 square metres might cost £1,200 to £2,500 in total. A larger extension roof of 30-40 square metres could run from £3,000 to £6,000. Deck replacement, new roof lights and complex drainage work will add to these figures. Get a breakdown of the costs in the quote so you know what each element is contributing.
Whether you repair or replace a flat roof, routine maintenance extends its life significantly. An inspection once or twice a year, ideally in autumn before leaf fall blocks outlets and in spring after frost, allows small problems to be caught early. The inspection should look for blisters, splits, any lifting at flashings or upstands, and any debris or moss that is blocking drainage.
Keeping gutters and outlets clear is the single most effective maintenance task a homeowner can carry out themselves. Standing water accelerates every kind of membrane deterioration. A roof that drains freely after rain will outperform a structurally identical roof where water sits for days at a time.
Moss and algae are more common on flat roofs than on pitched ones because the surface stays wet for longer. Moss can be carefully removed with a soft brush and treated with a biocide wash. Avoid power washing a flat roof membrane as the pressure can lift edges and damage the surface.
When you receive quotes, check what is actually included. A repair quote should tell you the area being addressed, the materials being used, whether any deck work is included, and how the new material integrates with the existing membrane. A replacement quote should list strip and disposal, deck inspection and any replacement allowance, insulation specification, membrane system, edge trims and flashings, and drainage arrangements.
If a quote is a single line saying "flat roof repair" with a price, ask for more detail before you agree to anything. Not because contractors are dishonest, but because you need to know what you are buying before you can judge whether it is priced fairly or whether two quotes are actually covering the same scope of work.
If you have a flat roof on a garage, extension or outbuilding in Dickleburgh that is leaking or showing signs of wear, getting a proper inspection is the right first step. We serve Dickleburgh and the surrounding area including nearby Diss. We will assess the condition of the existing roof honestly, explain what the options are and what each will cost, and let you make the decision with the full picture in front of you. Call us to arrange a roof survey.
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Call any time. Calls are answered day and night and passed straight to our roofers.
