Short answer
A warm flat roof has six parts: the structural deck, a vapour control layer, thermal insulation, a separation layer where needed, the waterproofing membrane with its fixing, and drainage. Each layer is chosen for the others.
1. Structural deck
Profiled steel, concrete or OSB / plywood. It carries the loads and is the fixing substrate for the membrane.
Protan NSAI certificate: galvanised steel deck min. 0.7 mm; plywood / OSB 3 min. 18 mm with screws penetrating ≥ 15 mm beyond the underside; in concrete, fasteners anchor in solid concrete.
2. Vapour control layer
Keeps indoor moisture out of the insulation. It must be continuous and turned up at walls, shafts and penetrations to the top of the insulation.
3. Insulation
PIR boards (termPIR AL, λD 0.022 W/(m·K)) or mineral wool, often combined — non-combustible wool at upstands and penetrations. Thickness follows the required U-value.
4. Separation layer
Needed where a PVC membrane goes over polystyrene or old bitumen (SINTEF TG 2010).
5. Membrane and fixing
Protan SE is mechanically fastened in the laps, with fastener density calculated for wind uplift in each roof zone. Ballasted roofs use Protan G held down by ballast.
6. Drainage
Falls, outlets at the low points and an emergency overflow.
Explore every layer in the 3D roof anatomy or configure your roof in the Roof System Studio.