Define the area being priced first
Does the price cover the entire roof, the area beneath the modules or a PV field with additional perimeter strips? This distinction alone changes the material quantity. Quotations become comparable when they use the same plan and scope.
Also record whether the membrane will be renewed and whether an existing PV system needs partial removal. An inexpensive board beneath new waterproofing may make sense on a new building, but on an intact existing roof it would trigger a very different level of intervention.
Two layers initially double the material requirement
Calculation assumption: one mineral layer costs €20 to €25/m² net. A second layer at the same price brings the material cost alone to €40 to €50/m² net. Across 1,000 m², that would mean €20,000 to €25,000 for one layer and €40,000 to €50,000 for two.
This range is an illustrative calculation assumption, not a verified manufacturer quotation or a VlamShield selling price. Cutting, waste, transport, fixing, waterproofing and labour are not yet included. The construction actually required determines how many layers are priced.
| Option | Material per m² | Material for 1,000 m² |
|---|---|---|
| One layer | €20–25 | €20,000–25,000 |
| Two layers | €40–50 | €40,000–50,000 |
| Additional cost of second layer | €20–25 | €20,000–25,000 |
Two layers do not always mean two directly beneath the membrane
In the published Efectis assembly using BarrierSheet, one mineral layer sits above the PIR insulation and another beneath it. This arrangement has a different installation sequence from two layers laid directly on top of each other. It does not establish a universal two-layer requirement for all projects. [1]
Request the specific build-up drawing. Only then can the layer count, required area per layer, fixing and additional work steps be established. The analysis of thin composite boards also explains the thermal side of the comparison.
Include labour, weather and repairability
For boards, include transport to the roof, cutting, laying, joints and fixing. For a mineral compound, add substrate preparation, mixing, application, thickness checks and curing. Weather allowances and interruptions can form a substantial share of the cost.
Consider later work too: how will a membrane seam be repaired? Will modules or larger areas need to be lifted? Is a connection accessible? A solution with a higher purchase price may be economically attractive if it simplifies installation or future interventions.
Compare the best alternative against the same task
A thicker board is not equivalent simply because it is thicker. A thinner layer is not more economical simply because it weighs less. Compare the required protective function, the full construction and the supporting evidence.
For an initial enquiry, provide the area, existing roof assembly, proposed PV layout, preferred layer position and a time window. These details allow DEK, SHEET, WEER and VLOEI to be compared meaningfully as different approaches.
At an assumed €20–25/m², a second equally priced layer over 1,000 m² adds €20,000–25,000 excluding VAT. Installation, fixing and waterproofing are additional.
Sources and technical documents
- Efectis · Klassifizierungsbericht 2025-R000982, BROOF(t1)www.allshield.com