Roof anatomy
Roof anatomy
Rotate, zoom, explode the layers and cut the section. Click a layer — function, errors, product.
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Schematic, not a construction drawingRoof build-up
Roof build-up
Illustrative schematic, not a construction drawing.
What it does
Collects water at low points. The emergency overflow works when the primary outlet is blocked.
Why it matters
Standing water loads the structure and ages details faster. Falls around outlets are formed in the insulation.
Common errors
- Outlet not at the low point
- No emergency overflow
- No sump formed around the outlet
Data and sources
- Sump around the outlet formed over ~500 mm by cutting ~40 mm from the top insulation layer (company practice)stogrenta.lt (2017) — company installation practice texts
What it does
Fixes the membrane through the insulation into the deck. Number and spacing follow the wind uplift calculation per roof zone.
Why it matters
Wind suction peaks at corners and edges — that is where most fasteners are needed.
Common errors
- Uniform spacing across the whole roof
- Non-system washers
- Fixing into too thin a substrate
Data and sources
- Protan SE 1.2: design capacity 627–912 N per fastener, depending on fastening system and substrate (tested in 0.75 mm steel and 18 mm plywood)SINTEF Technical Approval TG 2010 — Protan SE, T, SE-L and EX roofing membranes
What it does
Single-ply PVC waterproofing. Seams are hot-air welded — no open flame.
Why it matters
The membrane takes wind, UV, temperature and standing water. Watertightness is decided at seams and details, not in the field.
Common errors
- Seams not probed / peel-tested
- Laps too narrow
- Non-system detail components
- Membrane laid parallel to deck ribs in standard overlap fixing
Data and sources
- Laps: ≥ 120 mm side, ≥ 80 mm end; finished weld 20–40 mm wideNSAI Agrément Certificate 06/0262 — Protan SE and EX Roof Waterproofing Systems
- On steel decks the membrane runs at 90° to the profile (in the Secret-Fix system — along it)NSAI Agrément Certificate 06/0262 — Protan SE and EX Roof Waterproofing Systems
- Seams checked with a metal probe; peel tests every 200 m of machine weldingNSAI Agrément Certificate 06/0262 — Protan SE and EX Roof Waterproofing Systems
- SINTEF recommends a minimum fall of 1:40 (Norwegian recommendation)SINTEF Technical Approval TG 2010 — Protan SE, T, SE-L and EX roofing membranes
Protan PVC roofing membranes · Parapet · Roof outlet · Expansion joint · Rooflight upstand · Wall abutment · Pipe penetration · Cable penetration
What it does
Separates the PVC membrane from polystyrene or old bitumen and prevents plasticiser migration.
Why it matters
Without it PVC on EPS/XPS or bitumen loses flexibility. On EPS this layer (glass fleece ≥ 120 g/m²) is also part of the BROOF(t2) classified build-up.
Common errors
- Omitted on EPS
- Omitted on old bitumen or rigid PVC
Data and sources
- Protan SE needs a separate migration barrier/levelling layer on polystyrene and in re-roofingSINTEF Technical Approval TG 2010 — Protan SE, T, SE-L and EX roofing membranes
- BROOF(t2) on EPS: Protan SE 1.6–2.4 mm + glass fleece ≥ 120 g/m²SINTEF Technical Approval TG 2010 — Protan SE, T, SE-L and EX roofing membranes
What it does
Main thermal layer: polyisocyanurate core faced on both sides with multilayer aluminium foil.
Why it matters
Low conductivity reaches the same thermal resistance with a thinner layer — less load, shorter fasteners, lower upstands.
Common errors
- Boards not butted tightly — thermal bridges
- Joints not staggered between layers
- Combustible insulation not replaced with non-combustible at penetrations and upstands where the fire strategy requires it
Data and sources
- λD = 0.022 W/(m·K), thickness 20–250 mm, core density 30 kg/m³termPIR® AL insulation boards — technical card (GOR-STAL)
- Compressive strength at 10 % deformation: ≥ 150 kPa (30–139 mm), ≥ 140 kPa (140–250 mm)termPIR® AL insulation boards — technical card (GOR-STAL)
- Edges: FIT (square), LAP (rebated), TAG (tongue and groove)termPIR® AL insulation boards — technical card (GOR-STAL)
termPIR AL — foil-faced PIR insulation boards · Parapet · Roof outlet · Pipe penetration
What it does
Keeps moisture from heated rooms out of the insulation so it does not condense under the membrane.
Why it matters
Condensation under a membrane often looks like a leak although the membrane is intact. The VCL must be continuous and turned up at walls, shafts and penetrations to the top of the insulation.
Common errors
- Laps not sealed
- VCL interrupted at parapets or penetrations
- VCL between two insulation layers with the inner layer too thick
Data and sources
- Where the VCL sits between two insulation layers, the inner layer is at least 3× thinner than the outer (company rule — verify by condensation calculation)stogrenta.lt (2017) — company installation practice texts
What it does
Carries the whole roof build-up, snow and wind loads and transfers them to the steel frame.
Why it matters
Deck deflection and fixing decide whether the insulation and membrane work without stress. Profile geometry, span, load, deflection limit and coating must be stated in the design.
Common errors
- Deck from another manufacturer used without recalculated loads
- Deck not fixed at every support
- Side laps stitched at more than 300–400 mm
Data and sources
- Protan NSAI certificate: galvanised steel deck, minimum nominal thickness 0.7 mmNSAI Agrément Certificate 06/0262 — Protan SE and EX Roof Waterproofing Systems
- Side laps stitched every 300–400 mm (company practice)stogrenta.lt (2017) — company installation practice texts