Flat roofs and EPDM in Bury St Edmunds, Ely and Thetford

How flat roofs and epdm works

The reason EPDM took over from felt is joints. A felt roof is built from overlapping sheets, and every lap is a future leak. An EPDM roof on a domestic extension is normally one sheet with no joints at all in the field of the roof, which removes the commonest failure point entirely.

Almost every flat roof we replace fails at the edge or the upstand rather than in the middle. A mortar fillet where the roof meets the wall will crack, and once it does the water goes behind the covering. Aluminium trims and a properly dressed upstand cost a little more and are the difference between fifteen years and thirty.

The deck matters as much as the membrane. If the old boards are soft, laying a new membrane over them just hides the problem and you will feel it underfoot within a year. We lift and check the deck as standard and price the replacement boards openly, so nobody is surprised halfway through.

Falls matter more on a flat roof than most people expect. A flat roof is not actually flat; it needs a fall to the outlet, usually built up with firrings on the joists. If the fall is wrong the water sits, and standing water finds every weakness there is. Where the existing falls are wrong we correct them rather than lay a new membrane over the problem.

The other thing that decides how long a flat roof lasts is what happens at the outlet. A poorly formed outlet, or one that is higher than the deck around it, will hold water no matter how good the membrane is. We form the outlet properly and test that the roof drains before we leave it.

What the job includes

• Strip the old felt or asphalt back and take away the waste
• Inspect the joists and firrings, and replace the deck where it is soft
• New OSB3 deck laid and fixed
• EPDM membrane bonded down in a single sheet with no field joints
• Aluminium drip trims and edge detail, not a mortar fillet
• Upstands dressed into the wall and flashed in properly
• Outlets and guttering connected and tested

Signs you need it looking at

• Blisters, bubbles or splits in the existing felt
• Water sitting on the roof for days after rain
• The deck feels soft or springy underfoot
• Staining on the ceiling of the room below
• The felt has pulled away at the edge or the upstand