MIDA Standard PVS3 bitumen underlay — 3 mm, 15 m² roll

A bitumen underlay is an important part of a multi-layer roof waterproofing system. It sits beneath the top layer and helps create a durable, continuous waterproofing build-up. Although usually hidden once the work is complete, it affects the performance of the entire covering. At SteelProfil, we help match the underlay to the substrate, the remaining layers and the installation method so that the purchase suits the particular roof, not just a general product name.

Bitumen underlays come with different reinforcements, thicknesses and mechanical properties. Polyester fleece and glass-based carriers behave differently under tension and dimensional changes. SBS modification of the bitumen can improve flexibility. Selection should follow the roof system requirements. A suitable underlay works with the cap sheet, while carefully formed laps help maintain continuous protection against water.

This group includes products designed for different fixing methods, including self-adhesive and torch-applied membranes. The method can therefore be matched to the working conditions and the substrate’s sensitivity to heat. A self-adhesive variant can be useful where the system calls for reduced use of an open flame. Whatever the technology, the substrate requires proper preparation. Adhesion and joint durability depend on material compatibility, surface cleanliness and installation conditions.

Bitumen underlays are used on roofs of homes, garages, warehouses, workshops and outbuildings. They can form part of a new build-up or a planned refurbishment. In some solutions, suitable bituminous membranes are also used for other damp-proofing applications where the product documentation confirms this. However, an application should not automatically be extended to every product with a similar name. The manufacturer’s stated intended use is decisive.

A multi-layer covering should be considered as a complete assembly. A bitumen underlay is generally not intended to remain permanently exposed as the final roof layer. It needs a compatible cap sheet, suitable detailing and connections to flashings. Where thermal insulation boards form part of the build-up, check compatibility of their facing and the fixing method. This selection process helps the installer and avoids a false saving on an unsuitable underlay.

Planning the purchase together with the cap sheet simplifies logistics and reduces the risk of missing materials during roof work.

At SteelProfil, we offer bitumen underlays and help select the remaining roofing materials. We confirm availability of specific products when you enquire, and our broad assortment also includes first- and second-grade materials available from stock. Numerous promotions and attractive prices help match the purchase to the work budget. Tell us which substrate will receive the waterproofing and which top layer is specified in the design. We will prepare an offer covering the required quantity, membrane use and planned completion date.