Flat roofing
Flat roofs, EPDM and GRP
EPDM in one sheet, GRP laid wet, or single-ply welded at the laps, over a firring that actually moves the water to an outlet.
How it works
A flat roof is not flat. BS 6229 wants a finished fall of 1:80, which means designing 1:40 so that deflection and workmanship do not eat it. Most of the flat roof failures we are called to are ponding, not membrane defects. Firrings are what give a level deck its fall; leaving them out saves money once and costs it every winter after.
On EPDM the sheet comes in one piece for most domestic roofs, so there are no field laps to fail at all: the risk moves to the upstands and the outlet, which is where we spend the time. On single-ply we weld the laps with hot air and probe every one with a hook before we come off the roof.
Water still standing 48 hours after rain is a fall problem, not a membrane problem. No system guarantee covers ponding.
- Systems
- EPDM 1.2 mm, GRP 450 g, single-ply 1.5 mm
- Fixing
- Fully adhered or mechanically fastened
- Laps
- Hot-air welded and probed, or one-piece EPDM
- Fall
- Designed 1:40 for a finished 1:80, BS 6229
- Insulation
- PIR to the U-value in Part L
- Guarantee
- 20 years on the membrane, 10 years on our work
