TEP ROOF OY · MATERIAL AND INSTALLATION GUIDE
Vapour control in a profiled metal deck roof
Profiled metal decking alone does not determine the vapour control layer. First establish the surface on which it will be installed and the loads and exposure it will face during construction and use.
Identify the layers
- A rigid mineral wool board or building board intended to support the vapour control layer can be installed above the profiled deck. This support layer is distinct from the main thermal insulation and waterproofing substrate above the vapour control layer.
- Identify the structural deck, immediate substrate for the vapour control layer, vapour control layer, thermal insulation and roof covering separately on the drawing. Selecting only mineral wool and metal decking leaves the support layer and junction details unresolved.
Three options to compare
- A bituminous vapour control membrane, such as a BH1-class product, is a reasonable option to compare where sealing around fixing penetrations and durability during construction are priorities. For a membrane with welded laps, determine jointing and hot-work conditions according to the substrate used.
- A reinforced aluminium-laminated plastic film provides high water vapour resistance and taped joints. A separate option is a self-adhesive bitumen-aluminium vapour control layer approved by its manufacturer for direct application to profiled metal. Support longitudinal joints on profile crowns and transverse joints on product-specific support strips; priming follows the system instructions.
How to narrow down the options
- Start with the internal moisture load, roof ventilation and loads during construction. Ordinary PE film cannot replace a reinforced film on the basis of its material name alone. Confirm the product class, puncture resistance and approved installation method for this particular substrate.
- A product fixed directly to the metal deck is a specific system solution: its instructions do not demonstrate that all films or membranes are suitable for the same installation. Compare support layers, primers, jointing accessories and penetration components in quotations so that the scopes match.
Prepare for installation
- Provide the deck profile details, a roof section and a penetration layout. State in the request for a quotation whether the support layer, perimeter connections and interfaces with other trades are included in the roofing contract. Agree who checks the substrate before covering.
- Discuss the installation season, roof traffic and the sequence of protection work. If the vapour control layer is also required to provide temporary waterproofing, request a separate product and drainage plan. A vapour control product class alone is not a site weather protection plan.
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.
- Kattoliitto ry: Toimivat katot 2025 (Functional Roofs): vapour control layer substrate, installation and application classes, pp. 20-26 Checked 19.10.2026
- Kerabit Oy: Bituminous vapour control membranes: solid substrates and bituminous options Checked 19.10.2026
- Oy Sika Finland Ab: Sarnavap-5000 E SA: self-adhesive vapour control layer, Finnish product data sheet, 05/2020 Checked 19.10.2026
- BMI Suomi Oy: Products for low-slope roofs: bituminous and reinforced aluminium-laminated vapour control layers, p. 8 Checked 19.10.2026