Diss Roofers installs and repairs flat roofs on extensions, garages and outbuildings in Attleborough, using felt and EPDM rubber systems built to last.
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A flat roof done well is a practical, cost-effective covering for a single-storey extension, detached garage or outbuilding. Done badly, it becomes a recurring source of leaks, damp and costly internal damage. The difference almost always comes down to the quality of the installation and the choice of system - not luck.
On this page we walk you through exactly what a flat roofing job looks like from start to finish: every stage, what good work looks like at each one, and what to watch for if you are getting quotes from anyone.
We install two main flat roofing systems: torch-on felt (also called built-up felt or mineral felt) and EPDM rubber. Each suits different situations.
Both systems need a sound, level deck beneath them. The deck is the structural base - usually OSB boarding or marine plywood - and its condition matters as much as the membrane on top of it.
Understanding what a roofer should actually do on a flat roofing job helps you judge whether you are getting a proper service. Here is exactly what the work involves, in order.
Before any quote is given, the roof needs to be looked at properly. For a new installation on an extension or outbuilding under construction, this means checking the deck framing, the falls (the slight slope built into a flat roof to drain water away), and any upstands or abutments - the points where the roof meets a wall.
For a repair or replacement on an existing flat roof, the assessment is more involved. The membrane is checked for cracking, blistering, pooling water and open seams. The roofer should also check beneath the surface where possible, because a membrane that looks worn on top may be hiding a deck that has started to rot. A deck that has absorbed moisture will feel soft underfoot. This is critical information, because relaying a new membrane over a rotten deck wastes everyone's money.
Falls are worth understanding. Building Regulations require flat roofs to have a minimum fall of 1:80, meaning the surface drops at least 1 cm for every 80 cm of run. In practice, a fall of 1:40 is much better because it gets water moving to the outlet before it sits and stresses the membrane. If a roof was originally built without adequate falls, the only lasting fix is to rebuild the deck with tapered insulation or repositioned joists.
On a replacement job, the old membrane and insulation come off before anything new goes down. Layering new felt over old felt is poor practice: you cannot inspect the deck, you add weight to the structure, and any moisture trapped between layers will accelerate decay. A roofer who suggests simply overlaying should explain exactly why that is appropriate for your specific situation - it is occasionally justified on very large roofs where access is limited, but it is not a shortcut to take on domestic extensions and garages.
Once the old material is stripped, the deck boards are inspected individually. Any boards that are soft, crumbling or showing signs of wet rot are cut out and replaced with new OSB or marine-grade ply. This is not an optional extra - it is part of doing the job properly.
All stripped material is bagged and taken away. Old felt and insulation cannot go into a standard skip without separation, and a professional roofer will arrange removal as part of the work.
Once the deck is sound, it needs to be clean, dry and properly conditioned before any membrane goes down. For torch-on felt, a priming coat of bitumen primer is applied to the deck surface. This improves adhesion and helps seal the deck itself against moisture. The primer needs time to dry - rushing this step causes bonding failures later.
For EPDM installation, the deck is swept and checked for any protruding fixings that could puncture the membrane. Insulation boards are often added at this stage too, laid onto the deck before the membrane. Insulation beneath the membrane (called warm roof construction) is now the standard approach because it keeps the deck warm, preventing the condensation that degrades cold-roof decks from the inside.
For torch-on felt, the installation happens in layers. A base layer is fixed mechanically to the deck, then a second - and often a third - layer of felt is torched over it, each one bonded fully to the one beneath. The torch heats the underside of the felt until the bitumen flows slightly, creating a continuous bond. The top layer is finished with a mineral surface, usually grey or green chippings bonded into the bitumen, which provides UV protection.
For EPDM, the membrane is cut to the shape of the roof on the ground, then positioned and either fully adhered to the deck using a contact adhesive or mechanically fixed. Seams, where two pieces of membrane meet, are bonded with seam tape and a lap sealant. Getting seams right is the single most important part of the installation: a seam that peels back even slightly will let water in.
At every penetration through the membrane - a soil pipe, a rooflight kerb, a drainage outlet - the membrane needs to be sealed with a proprietary collar or flashing detail. These details are where shortcuts show up fastest.
Where the flat roof meets a wall, the membrane needs to turn up and terminate. This vertical section is called an upstand, and it must extend at least 150mm up the wall to prevent wind-driven rain from getting behind it. The top of the upstand is covered by a flashing - typically lead or aluminium - which is chased into the mortar joint above and sealed.
Lead flashings are the standard choice for most domestic work in the UK. Lead is soft enough to bed tightly to irregular masonry, and it will outlast most roofing membranes when correctly dressed and secured. A flashing that has simply been pushed into a joint and mastic-sealed at the top is not finished: it needs to be pointed with mortar to be watertight long-term.
Box gutters and internal outlets on flat roofs also need careful detailing. An outlet that is not properly integrated into the membrane will leak at the joint every time heavy rain hits it.
Water has to go somewhere. On a simple garage roof it may run off at the eaves into a standard fascia gutter. On an extension that abuts the house, drainage often needs to go through the membrane at an internal outlet and down a pipe. The outlet fitting is bonded into the membrane with a sleeve - this is a critical joint and needs to be done in the same material as the membrane wherever possible.
Blocked drainage is the most common cause of flat roof failure that is not down to the membrane itself. Leaves and moss build up around outlets and prevent water from getting away. Checking and clearing outlets once a year, particularly in autumn, is the single most useful thing a homeowner can do to extend the life of a flat roof.
Once the membrane, flashings and drainage details are complete, the whole roof should be walked and checked before scaffolding or access equipment comes down. Look for any areas where the membrane has not fully bonded, any upstands that are short, any seam edges that are lifting, and any outlets that have not been properly sealed.
On an EPDM installation, seams can be tested by running a finger along the edge: a properly bonded seam feels solid and does not flex away from the surface. On a torch-on felt job, the mineral surface should be consistent across the whole area with no bare bitumen visible.
Ask the roofer to walk you through what they have done at this stage. Any professional should be happy to explain the flashings, show you where the outlet is and confirm what fall the roof has been built to.
A flat roofing job generates a fair amount of waste: old felt, insulation offcuts, packaging and chippings. All of this should leave with the roofer. The surrounding area - paths, borders, gutters on adjacent roofs - should be cleared of debris before the job is called finished.
At handover, it is reasonable to ask what maintenance the roof needs, how to identify early signs of trouble, and what to do if you notice water ingress. A short conversation at this point can prevent a small problem from becoming a large one three years later.
Not every flat roof problem needs a full replacement. Small areas of cracking, a lifted seam or a failed flashing can all be repaired if the underlying deck is sound and the membrane is in good overall condition. Patching works best when the damage is limited and the rest of the roof has several years of life left in it.
Replacement makes more sense when the roof is approaching the end of its expected lifespan, when the deck has significant rot, when there are multiple failure points across the surface, or when pooling water has caused repeated leaks that patches have not resolved. A roofer who recommends full replacement on a two-year-old roof with a single leak is not being straight with you - equally, one who keeps patching a 25-year-old felt roof that pools badly is not giving you value.
The most important maintenance tasks on a flat roof are simple:
Catching a problem early is far cheaper than leaving it. A split seam that is repaired promptly costs a fraction of the rotten deck repair that follows if water gets underneath and is left for a season.
If you have a flat roof on an extension, garage or outbuilding in Attleborough that needs replacing, repairing or inspecting, get it looked at by a roofer before committing to any work. We will give you a straightforward assessment of what the roof needs and what it will cost.
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Call any time. Calls are answered day and night and passed straight to our roofers.
