Flexible Self-Adhering Roofing

Roll-based self-adhering materials used for installing waterproof membranes on residential and industrial roofs are commonly known as self-adhering roofing or flexible roofing. This technology has been known since the mid-20th century, when the well-known ruberoid first appeared on the construction market.

Over more than half a century of evolution and new developments in improving the properties and characteristics of self-adhering materials, dozens of products have emerged in the range of waterproofing manufacturers. The most widely used products are likely TechnoElast, produced by the Russian company TechnoNIKOL, and its main competitor, VillaFlex from the Danish company Icopal.

In this article, we will examine the basic structure of a flat roof with self-adhering waterproofing, discuss the design of the roof system on various substrates, and highlight key details and technical requirements for installing flexible roofing.

Flexible Self-Adhering Roofing: Layer by Layer

If we examine a cross-section of the complete flexible roofing system, we see approximately the following (from base to exterior).

The roof base is typically made from a concrete slab or profiled sheet. To ensure proper drainage of rainwater and melted snow, the base is constructed with slopes. In the case of profiled sheets, the slope is achieved through the profile itself (due to height variations in the structure). If the roof is made from a concrete slab, the slope is created using polystyrene, screed, or a prefabricated base made from moisture-resistant 24 mm plywood or cement particleboard.

The vapor barrier layer prevents moist air from entering the insulation mass located above, thus preventing condensation within the insulation. Vapor barriers are typically made from non-woven synthetic materials such as spanbond and their derivatives.

Single- or double-layer insulation. Insulation is laid over the slope and vapor barrier in one or, more commonly, two layers. The purpose of double-layer insulation is that flat roofs are load-bearing structures. Snow load in winter can reach up to 300 kg/m², meaning insulation must withstand loads of at least 60 kPa.

Rigid mineral wool boards with such compressive strength have a relatively poor thermal conductivity and high cost. Therefore, for economic efficiency, most of the insulation layer is made from lightweight material with a density of 70–100 kg/m³ and compressive strength of 20–30 kPa. The top second layer is no more than 40–50 mm thick and must have a strength of 60–70 kPa. Thus, the lower layer performs primarily thermal insulation, while the upper layer provides protection.

An alternative solution is to install a cement-sand screed over the inner layer of mineral wool. The screed also protects the wool from mechanical damage, but does not add thermal insulation to the roof structure, although it is cheaper than a second rigid insulation layer.

The choice of solution should be based on a thermal calculation to determine the minimum required thickness of the insulation mass for preventing structural freezing.

Self-adhering waterproofing. Mineral wool, like the protective screed, is non-combustible. Therefore, flexible roofing can be applied directly over them. The adhesive application of roll-based waterproofing materials is done using hot bitumen, heated to an optimal adhesion state by a propane torch reaching temperatures up to 600°C.

To improve adhesion, the roof base may be treated with bituminous mastic. Bitumen adheres much better to bitumen than to an untreated screed or mineral wool surface.

Installation Technology for Waterproof Membranes in Flexible Roofing

During installation of the waterproof membrane, it is crucial to maintain a clean surface and remove all debris present on the roof: branches, leaves, construction waste (most dangerous for such roofing: hidden screws and glass shards). Any foreign object under the membrane will inevitably compromise its integrity over time.

The second golden rule when bonding bituminous roll material to mineral wool is to prohibit direct flame contact from the propane torch on the mineral wool surface. Heating should only be applied to the self-adhering material itself.

If flame contacts the wool surface, it burns away the binder up to 3–5 mm deep, meaning the membrane is bonded to loose, unconnected fibers. The result of such an error is severe shrinkage of the self-adhering material in the first summer. Shrinkage, in turn, leads to loss of joint integrity between adjacent sheets and causes leaks.