Tembok Carpenter & Building Services
Flat roof repair and replacement
A flat roof that leaks or holds water is rarely fixed by patching the visible spot alone. The deck, falls, edges and outlets all play a part, so the right repair depends on finding why water is getting in or sitting on the surface.
Tracing a flat roof leak
Water on a ceiling can appear some distance from where it enters the roof, because it travels along the deck or joists before dripping. Common sources are failed joints in the covering, cracked flashings where the roof meets a wall, split upstands and blocked outlets. A careful inspection looks at these details as well as the open surface. Photographs taken during rain, and a note of when the leak appears, help narrow the cause before any covering is lifted.
A local repair can be sensible when the rest of the covering is sound and the deck beneath is dry. If the boards are soft, the felt is blistered across a wide area or there have been several repairs already, replacement is usually the better value. Ask what is under the covering before agreeing a repair, because a wet deck left in place will continue to cause problems under a new surface.
Ponding and the falls on a flat roof
Most flat roofs are built with a slight fall so water drains to a gutter or outlet. Ponding happens when that fall is too shallow, the deck has sagged or an outlet is set too high. Small, shallow puddles that dry within a day or two are not unusual, but standing water that remains for longer puts strain on joints and adds weight. To fix flat roof ponding properly, the fall needs correcting, often with tapered insulation or firrings under a new deck, rather than adding another layer on top.
Outlets and gutters should be checked at the same time. Leaves, moss and debris can block the route even on a well-built roof. Where a flat roof sits below a pitched roof, the volume of water arriving from above needs a suitable outlet and gutter size. Correcting drainage is often part of a replacement scope, so it is worth asking how the proposed design will move water away from the surface.
EPDM, warm roofs and replacement
EPDM is a synthetic rubber membrane laid in a single sheet where possible, which reduces the number of joints. How long an EPDM roof lasts depends on the quality of installation, the deck beneath, the detailing at edges and penetrations, and how well the roof is maintained. Whether EPDM can be laid over existing felt depends on the condition of that felt and the deck; often the old layers are stripped so the deck can be inspected and repaired. Our guide to laying EPDM over felt covers this question in more detail.
Replacement is a good time to consider a warm flat roof, where rigid insulation sits above the deck and the waterproof layer goes on top. This keeps the structure warm and reduces the risk of condensation within the roof. It raises the roof level slightly, so edges, upstands and any adjoining windows or doors need checking. Tembok offers a free site visit to look at the roof, the ceiling below and the drainage, followed by a written quote for the repair or replacement.
Flat Roofing — frequently asked
Can you lay EPDM over felt?
Sometimes, if the felt is flat, well bonded and the deck beneath is dry and sound. Often the felt is removed so the deck can be inspected and any damaged boards replaced before the membrane goes down.
How long does an EPDM roof last?
It depends on installation quality, the deck, the edge and outlet detailing, exposure and maintenance. Ask the installer about the specific membrane and any manufacturer guidance on expected life.
How do I fix ponding on a flat roof?
Clear outlets first. If water still stands, the fall needs correcting, usually with tapered insulation or firrings beneath a new covering. Adding coatings on top does not change the drainage.
What is a warm flat roof?
It is a build-up where insulation sits above the deck with the waterproof membrane on top, keeping the structure on the warm side and reducing condensation risk.
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