If your flat roof in Norwich is showing damp patches, blistering felt or pooling water, getting the right diagnosis early is the difference between a straightforward repair and a full replacement.
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Flat roofs are not inherently short-lived. The old felt systems fitted to extensions and garages from the 1970s through to the early 2000s have a typical lifespan of around 10 to 15 years. Many are now well past that, and they show it. Understanding what you are seeing when something looks wrong saves you from either ignoring a problem until it becomes serious, or paying for a full replacement when a targeted repair would have done the job.
A small amount of water sitting on a flat roof after rain is normal if it drains within 24 to 48 hours. When water sits for longer, the roof either lacks sufficient fall or the drainage outlet is blocked. Flat roofs are specified with a minimum fall of 1:80, roughly 12mm of drop per metre, to encourage run-off. If the deck has sagged or the original fall was too shallow, water will pond repeatedly. Over time, ponding accelerates the breakdown of felt membranes and can work its way into laps and seams. If your roof drains slowly but completely, clearing the outlet and monitoring it may be enough. If water is sitting for days, the deck or fall needs a proper look.
Blisters in a felt roof form when moisture trapped between layers of felt turns to vapour on a warm day and pushes the surface up. They are a sign that the membrane has already been compromised somewhere - either the felt was laid over damp substrate, or water has tracked in through a split or lap failure. Small blisters that are stable and intact are not an emergency, but they should be noted and monitored. A blister that has burst, or one sitting over a felt lap, is a live leak risk. The underlying cause - the moisture pathway - needs to be found, not just the blister patched over.
Felt and older modified bitumen membranes become brittle as they age. UV exposure dries out the surface, the material loses flexibility, and it cracks under thermal movement - the expansion and contraction the roof goes through between a cold winter night and a warm summer afternoon. Cracks at seams, around upstands, or at the point where the roof meets a parapet wall are the highest-risk areas because water tracks in and sits on the deck rather than running off. If you can see daylight-coloured hairline splits on the surface, the membrane is near the end of its serviceable life.
A damp patch on the ceiling directly below a flat roof is an obvious sign. Less obvious is a stain that appears on an internal wall near where the flat roof adjoins the main house - water can track horizontally along the roof deck before it finds a way through. Damp is sometimes mistaken for condensation, particularly in kitchens and bathrooms that vent into a cold roof space. A roofer can usually distinguish between the two by checking the deck from above and feeling the insulation if access allows. Never assume ceiling damp is condensation without having the roof checked first.
The flashing is the lead, mortar or code strip that seals the junction between the flat roof covering and whatever it meets - a wall, a chimney stack, a skylight frame. This is one of the most common points of failure on any flat roof. Mortar flashings crack and drop out. Lead flashings can lift if they were not bonded or chased in correctly. A flashing failure lets water track straight down the wall behind the roof covering, often appearing as a damp patch well away from the actual gap. If your flat roof is otherwise in reasonable condition but you have internal damp, check the flashings first.
Several factors speed up the deterioration of flat roofing beyond normal wear:
A repair is appropriate when the membrane is structurally sound across most of its area and the failure is localised - a cracked lap, a lifted flashing, a split around a pipe collar. A replacement is the right call when the felt has lost flexibility across the whole surface, when the deck beneath is soft or rotten, or when the roof has already had multiple patch repairs and is simply at the end of its life. Patching a tired old felt roof repeatedly costs more over five years than a single properly installed modern system.
Modern flat roofing membranes - EPDM rubber in particular - perform substantially better than the felt systems they replace. EPDM is a single-ply rubber membrane that stays flexible in cold weather, does not crack under UV exposure, and when correctly installed and detailed handles thermal movement without splitting. Typical costs for a flat roof installation or full replacement in Norfolk run from around £70 to £120 per square metre depending on the system, the condition of the existing deck and the complexity of the detailing - though every job is different and figures should be treated as a starting point rather than a firm figure until the roof has been seen in person.
Whoever you speak to about a flat roof in Norwich, ask them to confirm what they found on the deck - whether it is sound, whether insulation needs replacing, and whether the drainage fall is adequate. A price that does not include deck replacement may look attractive but will leave you with a new membrane over a rotten base. Ask what system they are installing and what the manufacturer states about its expected service life. Ask whether new outlets and flashings are included or priced separately.
If you are in Norwich and have concerns about a flat roof on an extension, garage, dormer, or outbuilding, call us for a flat roof survey. We cover Norwich from our base in nearby Wymondham and can assess whether you need a repair or a full replacement.
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Call any time. Calls are answered day and night and passed straight to our roofers.
