Details
The details that keep the water out.
A flat roof rarely leaks in the middle. It leaks at a wall, an edge, a pipe or an outlet. These are the details we build, drawn in section, with the measurements we work to.
- EPDM membrane
- QuickSeam tape and flashings
- Sealants
- Metal parts and fixings
Lap seam
Where two sheets meet. The joint is made with QuickSeam Splice Tape, cold, without flame or hot air.
- Overlap at least 100 mm.
- Tape 76 mm wide. 5–15 mm of tape must show past the edge of the upper sheet.
- Both surfaces cleaned and primed with QuickPrime and a QuickScrubber until an even dark grey, then left to flash off (usually under 10 minutes).
- Pressed down with a silicone hand roller along the full length.
- Where two rolls of tape meet: 25 mm overlap and a FormFlash patch on top.
Upstand at a wall
The membrane turns up the wall and is held at both ends: at the base and at the top.
- Membrane bonded at least 150 mm above the finished roof.
- Fixed at the base with a perimeter strip, fixings no more than 300 mm apart and within 30 mm of the corner.
- At the top: a termination bar with fixings no more than 200 mm apart, Water Block behind it and sealant along the top.
- The bar is cut at every corner, with a gap of at least 5 mm.
Roof edge
Where the roof stops at a metal edge trim.
- Trim fixed no more than 100 mm apart.
- QuickSeam Flashing, 127 mm wide, runs over the trim flange and at least 50 mm onto the membrane.
- QuickSeam Flashing is only used on straight runs, never stretched round three-dimensional corners.
Pipe through the roof
Round pipes get a moulded EPDM pipe flashing, so there is no cutting and patching on site.
- Pipe Flashing fits pipes from Ø 25 to 152 mm. Smaller conduits from Ø 13 to 64 mm get a Conduit Flashing.
- Stainless clamp at the top, Lap Sealant around the flange edge.
- Odd shapes and groups of pipes get a Penetration Pocket filled with Pourable Sealer.
Roof drain
The outlet is where all the water goes, so it is sealed twice: under and over the membrane.
- Water Block in a continuous bead on the drain flange.
- Membrane runs about 20 mm into the bowl.
- Clamping ring bolted down over the membrane.
T-joint
Where three sheets meet, the step in the seam is covered with a patch.
- FormFlash patch about 150 mm across, 75 mm each way from the joint.
- Lap Sealant on the cut edge of the patch.
Fixing in the seam
One of the mechanical options: a batten fixed down inside the lap.
- Overlap at least 200 mm.
- Wide tape: 152 mm.
- The number and spacing of fixings come from the wind load calculation.
Walkway pads
Rubber pads where people walk: to plant, to vents, to solar panels.
- Pads 762 × 762 mm.
- Gaps of 25–150 mm between pads so water can drain.
- If a pad would sit on a seam, a cover strip goes on first, running at least 150 mm past the pad.
See the whole build

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