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Planning a new flat roof for an extension, garage or dormer means resolving the whole build-up before the visible covering. Compare structure, insulation, rooflights, drainage and wall junctions early to reduce the risk of water entry, heat loss and unworkable details.
An extension, dormer, garage and plant roof can need very different construction even when the roof areas are similar. The first questions concern structure, internal use, rooflights, walls, doors, outlets and whether anyone needs maintenance access. A waterproof roof is not automatically suitable as a terrace or balcony; any occupied use needs its own structural, safety and surface design.
A new flat roof normally combines supporting structure, deck, vapour control where required, insulation and waterproofing. The order and compatibility of these layers affect condensation, heat loss, movement and the finished height. Responsibility for structural, thermal, fire and drainage design should be clear before work reaches the roof, particularly where several designers or trades meet.
Rain needs a deliberate route off the roof. Roof shape, low points, outlet positions, gutters and any required overflow arrangement should work around rooflights, parapets and changes of level. Poorly placed outlets or restricted falls can leave standing water even beneath a new covering. Outlet pieces must also suit the selected waterproofing and remain accessible for cleaning.
Wall abutments, rooflight kerbs, pipes, edge trims, parapets and door thresholds interrupt the main roof surface. Insulation and falls consume height at these points, so late decisions can leave too little space for a reliable upstand. Each junction should show how water is turned away and which trade creates the surface that receives the waterproofing.
GRP, felt, EPDM and single ply behave differently around movement, corners, long runs and penetrations. They also use different decks, jointing methods and accessories. Weather during installation, roof access and later maintenance can affect practicality. The choice should follow the building and complete build-up rather than a product name selected before the roof details are known.
Useful handover information can show the final roof build-up, product references, outlet positions, concealed-stage photographs, approved changes and care restrictions. Keeping this with the property papers makes later maintenance and repairs easier because the covering and layers do not need to be guessed. For an early discussion, drawings, intended use and project stage are more useful than a preferred brand.
Before choosing flat roof installation, note the visible defect, when it appears, nearby junctions and any safe indoor signs. If the cause remains unclear, request a roof inspection that distinguishes a local repair from a wider issue; do not climb onto the roof to investigate.
Compare flat roof options Compare new-roof, repair and replacement choices.
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What a flat roof survey can tell you Understand roof shape, access and existing junctions.
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Roof survey checklist See the main questions for a roof inspection.
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Tell us about a flat roof problem Tell us about the building and project stage.
/contact/Roof use, structure, insulation, drainage, edges, rooflights, access and project-specific design requirements come first.
No. Occupied use needs suitable structural, guard, access, surface and waterproofing design.
Insulation, falls and waterproofing upstands use vertical space, so late coordination can leave an unworkable junction.
Keep the final build-up, product references, outlet map, concealed-stage photographs, approved changes and care guidance.