TEP ROOF OY · PROJECT PLANNING GUIDE
Structural deck and vapour control layer
The load-bearing structure, the substrate for the vapour control layer and the substrate for the waterproofing are different things. Establish their compatibility before selecting materials and installation methods.
The substrate affects installation
- On profiled metal decking, the vapour control layer needs the support specified in the design. Insulation and fixing arrangements depend on the deck profile and loads.
- Check the suitability and moisture condition of concrete and timber substrates before covering them. Determine the waterproofing fixing method and hot-work safety measures according to the substrate and site conditions.
The vapour control layer must be continuous
- The purpose of the vapour control layer is to limit harmful water vapour entering the roof build-up. Select the product according to the internal moisture load, roof construction and ventilation.
- Sealed joints, edges and penetrations are essential to the performance of the complete layer. A material name or the properties of an individual board alone do not demonstrate the airtightness of the whole roof.
Agree before work begins
- Record the substrate acceptance criteria, junction details, inspections and work sequence. Establish how the build-up will be protected during interruptions and who is responsible for temporary junctions.
- If the vapour control layer is also to serve as temporary weather protection, separately confirm the suitability of that specific product and the entire temporary build-up.
Use and design responsibility
TEP Roof Oy guide cards support project preparation and the definition of contract scope. They are not project-specific construction designs. The project structural designer is always responsible for checking the suitability of the solutions presented and adapting them to the project's structures, loads and requirements. Construction requires project-specific design and approval, together with the current manufacturer's instructions for the selected products.
Sources
An editorial compilation by TEP Roof Oy. The product- and system-specific source instructions must be checked for the selected solution.
- Kerabit: Bituminous vapour control membranes Checked 12.10.2026
- Saint-Gobain Finland Oy / ISOVER: Low-slope roofs: system guide 07/2026 Checked 12.10.2026
- BMI Suomi: Installing bituminous membranes on low-slope roofs Checked 12.10.2026
- Ministry of the Environment / Finlex: Moisture performance of buildings: Decree 782/2017 Checked 12.10.2026