Roof underlay sheet MIDA Standard PVS3 — 15 m² at 3 mm

Efficient installation of a bituminous roof starts with a layer on which the following work can proceed consistently. The underlay provides the base for multilayer waterproofing and contributes to protecting the roof against water. Different fixing methods help match it to the structure and materials beneath.

An underlay is intended to work beneath the cap sheet. It allows the strip layout to be established and provides a continuous base for the remaining covering. In a multilayer build-up, joints can be arranged so successive layers complement one another. This gives a clear sequence of work across the roof. The material can be used over large areas and in strips around details. Its role is hidden when the work is finished, but matters to the performance of the completed covering. Repeated strips make progress easier to check across successive areas. The large surface receives the same base, including around locations requiring extra attention.

Depending on the product, an underlay may be torch-applied, mechanically fixed or bonded using a self-adhesive layer. This variety makes it possible to design a solution for timber, concrete or suitable thermal insulation. A self-adhesive version helps reduce flame use when installing this layer, which can matter to the work sequence. The method follows the system and the particular substrate. The installation approach can therefore suit the construction without changing the basic function of the bituminous underlay.

The internal carrier gives the membrane its mechanical properties and helps it retain its form during installation. Polyester-reinforced versions combine this role with the flexibility of an appropriately modified bituminous compound. This is useful when shaping the material around edges and transitions between planes. The chosen product can provide a strong base for the next layer, including when refurbishing an old covering. Different membrane types allow the package to be matched to the expected roof movement and connections between individual sections. The underlay’s sheet form allows measured pieces to be carried and fitted without building the entire barrier from a compound applied directly to the substrate.

The underlay can be cut into strips at a parapet, equipment base or another feature projecting above the roof. Its flexible form helps establish continuous waterproofing before the final layer is installed. Details therefore become part of the complete build-up rather than an unrelated addition to a finished roof area. During modernisation, the material allows the arrangement to be adapted to new dimensions and height changes. The underlay requires its specified cap layer so that each part performs the task suited to its construction.

At SteelProfil, we offer underlays and materials for the complete roofing system at competitive prices. Stock availability, numerous promotions and first- and second-grade products in our range make selection easier. Explore the underlay options and prepare a sound base for the next stage of roof construction or refurbishment.