Insulation of a Mansard Roof

In mansard constructions, only tested and effective insulators are typically used: any experiment here may result in substantial heating bills during cold seasons. The vapor barrier layer is also particularly important—it prevents warm, moist air from the room from entering the insulation mass, thus avoiding condensation and subsequent moisture damage to the insulation.

A free ventilated air gap must exist between the outer surface of mineral wool and the under-roof waterproofing membrane. If the membrane is installed directly on the insulation surface, there is a risk of a greenhouse effect.

The core issue lies in the fact that almost all breathable waterproofing membranes are manufactured using a needle-punch method, which results in numerous micro-perforations through which moist air must pass. At the same time, moisture penetration from the reverse side into the insulation layer is almost impossible.

Installing the membrane directly on the insulation risks clogging these micro-perforations with insulation fibers. As a result, the membrane, which should continuously 'breathe,' no longer allows moisture vapor to pass through, leading to over-wetting of the insulation. Since water is an excellent thermal conductor, over-wet insulation loses its ability to protect the mansard structure from through-freezing.

Roof Cladding for the Mansard Floor

Most commonly, sheet materials are used for the final roofing layer in mansard construction: these include corrugated metal sheets (onduline), metal roofing, and euroshingles. Less frequently, tile-based bituminous materials such as flexible or composite roofing tiles are used.

The roof covering not only prevents moisture from entering the attic space but also plays a major role in resisting wind loads, which primarily affect the vertical roof slopes of the mansard system.

To prevent deformation of the entire roof geometry in mansard construction, so-called 'kossyunki' (diagonal braces) made from 100 x 150 mm timber are used to reinforce the structure diagonally. As for roofing material choice, sheet products are far more effective at distributing wind load across the entire roof surface, making them the preferred option in this context.

Another key function of the insulation material is to maintain a negative temperature on the external side of the roof covering. This is particularly important during snowy winters, because on an un-insulated roof with a positive surface temperature, snow melts continuously throughout the winter. As a result, ice and icicles form at eaves from dripping melted water, potentially damaging the drainage system and endangering residents' health.