Technonicol underlay Primaglas G200S4 — thickness 4.2 mm; roll 10 m²

The lower roof layer remains hidden, but contributes to protecting the whole roof. An underlay provides a prepared base for the following layers and helps maintain continuous waterproofing. In a garage, flat-roofed house or commercial building, it is an important part of the solution that supports comfortable use of the interior.

A membrane roll allows material to be laid efficiently across a large area. Individual strips are joined into a continuous layer according to the chosen system, before the covering is completed above. This division of functions helps prepare a watertight enclosure. The underlay works with the cap sheet to form a solution intended for long-term roof use, including at changes of direction and edges. Each layer has a clearly defined protective function within this build-up.

The reinforcement inside the sheet gives it specific mechanical properties. Depending on the version, it can support dimensional stability or provide the strength needed in the chosen system. SBS modification additionally increases the flexibility of the relevant products. This allows the underlay to be matched to the substrate and behaviour of the complete roof assembly. In practice, the client can choose an underlay suited to a rigid surface, upstand details and the required compatibility with the upper covering layer.

At parapets and transitions to vertical surfaces, the ability to shape the material is useful. The underlay can follow the detail, establishing continuity for the layers above. In a new building, this helps organise the most demanding areas from the outset. On a simple roof area, the benefit is a regular arrangement of strips; at a chimney or upstand, it is the ability to adapt the sheet to a change in the direction of the protected surface.

Different fixing methods broaden the range of applications. Depending on the product and system, membranes may be torch-applied, mechanically fixed or self-adhesive. A self-adhesive version can be especially useful where the installation method calls for reduced use of an open flame near the substrate. Choosing such a solution combines practical installation with the properties of the subsequent layers and prepares the roof according to its actual construction.

During modernisation, an underlay can become part of a new build-up after suitable preparation of the existing covering. It helps prepare the surface before the cap sheet is laid and connect it with the designed details. Its role is practical: it belongs to a complete waterproofing system and is not a standalone final finish for every roof. Carefully coordinated layers provide a sound basis for continued use of the building without changing its architecture.

SteelProfil supplies underlays at favourable prices, with numerous promotions helping you assemble roofing materials. We have products available from stock and first- and second-grade options in the wider range. Select the underlay and cap sheet together to prepare a compatible roof covering for your building.