If your flat roof in Diss is showing cracks, damp patches or pooling water, understanding what's gone wrong - and why - is the first step to fixing it properly.
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Flat roofs on extensions, garages and bay windows do not fail overnight. The problems that cause a leak usually develop over months or years, and by the time water appears on your ceiling, the membrane or felt underneath has often been struggling for some time. Knowing what to look for - and what's causing it - helps you act before a repair turns into a full replacement.
At Thetford Roofers, we survey flat roofs across Diss and the surrounding area, advise on what's actually wrong, and carry out replacements using systems that suit the roof and the budget. This page focuses on the warning signs homeowners most often miss, and the underlying causes behind them.
A flat roof is never truly flat. It should have a slight fall - typically at least 1 in 80, and ideally 1 in 40 - to direct rainwater towards an outlet or drip edge. When water sits in a pool for more than 48 hours after rain, something has gone wrong with the falls or the drainage.
Standing water is worth addressing early because it accelerates every other failure. It adds weight the deck may not be designed to carry, softens old felt, and forces water into any crack or joint that would otherwise shed it. A roof that ponds regularly will fail years sooner than one that drains cleanly.
Common reasons for ponding include: a deck that has sagged or deflected under load, an outlet that is blocked with debris, or a roof that was never laid with sufficient fall in the first place. Each has a different fix, which is why a proper inspection matters before any work begins.
You do not need to get on the roof to spot most early warning signs. From the ground or an upstairs window, look for:
Inside the property, damp staining on a ceiling below a flat roof, or a ceiling that feels soft to the touch, suggests water has already been getting in for some time. The entry point is rarely directly above the stain - water travels along joists before it drops.
Traditional mineral felt expands and contracts with temperature. Over many years, this movement causes the material to fatigue. Splits tend to appear first along the edges of the roof and at any point where two sheets overlap, because those are the areas under the most stress.
UV exposure degrades the top surface of felt, making it brittle. A roof that looked serviceable three years ago can deteriorate quickly once the surface mineralisation breaks down. When you press a finger firmly into old felt and the surface cracks rather than flexes, that felt is near the end of its life.
EPDM rubber membranes are significantly more resistant to this kind of degradation. A properly installed EPDM system stays flexible across a much wider temperature range, which is why it has largely replaced traditional torch-on felt on new installations.
The perimeter of a flat roof is where failures are most concentrated. At the edges, felt or membrane must be turned up and secured, or turned down over a drip edge. If this upstand is too short, too thin, or was never bonded properly, it will lift in wind or peel back over time, leaving a direct path for water.
Where a flat roof meets a wall - on a rear extension or bay window, for example - there is almost always lead or aluminium flashing. This flashing is dressed into a mortar joint in the brickwork. When the mortar fails, the flashing drops away from the wall and water runs straight down behind it. Repointing the mortar joint and re-dressing the flashing is a straightforward repair, but it is frequently overlooked until a significant leak develops.
Outlets - the drain points built into the roof surface - are another concentration point. Debris collects around them, the seal between the outlet and the membrane degrades, and if the outlet is cast iron or pressed steel it may have rusted through entirely. Checking and clearing outlets is something any homeowner can do safely from a ladder at the roof edge, and doing it twice a year reduces the risk of ponding significantly.
The membrane or felt sits on a deck, usually timber boards, plywood or oriented strand board (OSB). When water gets through the surface covering, even slowly, it saturates the deck. Wet timber rots, loses structural strength, and eventually becomes spongy underfoot or visibly deflected.
A roof that bounces or gives when walked on has deck damage. At that point, a surface-only repair will not hold for long - the deck needs to come up and the rotten sections need replacing before a new covering goes on. Skipping this step is the most common reason a newly recovered roof develops problems within a few years.
Before any flat roofing work is priced, ask the contractor what they found when they inspected the deck, and what condition they expect it to be in when the old covering is stripped. Any honest roofer will tell you they cannot fully assess deck condition until the old felt is off, but they can give you a view based on what they can see and feel.
Traditional three-layer mineral felt has a typical lifespan of 10 to 15 years, though roofs in exposed positions or with drainage problems can fail sooner. Torch-on felt, which is a single thick sheet applied with a gas torch, generally lasts 15 to 20 years when properly installed. EPDM rubber membranes are rated by manufacturers for 20 to 30 years and beyond, though the actual lifespan depends on how well the system was detailed and bonded at the edges.
If your roof is more than 15 years old and has not been inspected recently, a survey is sensible before any significant damp patches or internal damage appear. Catching a failing roof early usually costs less than dealing with the secondary damage - rotted deck, wet insulation, or damaged ceilings - that follows a prolonged leak.
Thetford Roofers covers Diss and the surrounding area. If you are unsure whether we cover your location, call us and we will confirm.
If you have spotted any of the warning signs above, call Thetford Roofers to book a flat roof survey in Diss. We will inspect the surface, falls, edges and any flashings, tell you honestly what we find, and advise on whether a repair or a full replacement makes more sense for your roof.
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Call any time. Calls are answered day and night and passed straight to our roofers.
