Types of Flat Roofs

Ventilated roof
(cold roof)

An aerated roof consists of a two-layer flat roof structure (upper and lower shell). The height of the aeration level, as longitudinal and transverse aeration, should be at least 15 cm. Usually an elevated wooden construction with formwork is applied to a reinforced concrete or wooden beam ceiling. Lower-cost fibre insulation materials can be used on the lower shell for thermal insulation. The amount of moisture diffusion needs to be calculated and properly connected to the outside air. Depending on the level it might require the installation of a PE with a low sd value under the insulation. A vapor seal is not required in that case. The aeration openings must be protected against the ingress of birds or other animals, with sieves or grilles.

Non-aerated roof (warm roof)

Standard roof

In the case of a standard, non-aerated roof, the waterproofing is directly above the insulation. A vapour seal must be installed on the supporting shell under the insulation. The design of the vapor seal and determination of the connection details for the structure's functional layers must be carried out by the planner. The type and size of insulation boards is determined by the planner according to the desired results.

Inverted roof

The difference to construction of the standard roof lies in the fact that the waterproofing membrane is installed on the base layer, directly on the substrate underneath weatherproof and environmentally resistant insulation, which is secured by suitable ballast system. A vapor seal is not required in this type. The type and size of insulation boards is determined by the planner according to the desired results.

Double / built-up flat roof or combination roof

The double or combination roof is a flat roof construction whereby the roof waterproofing is placed between two thermal insulation layers. The upper insulation layer must be weatherproof and environmentally resistant. As with the inverted roof, it must be mechanically fastened or protected from wind suction with sufficient ballast. It is covered with trickle protection / filter fleece to prevent small dust and dirt particles from seeping in. The roof construction serves in particular to improve the insulating capacity of normal, single-shell flat roofs. For this reason, it is also referred to as a "combined inverted roof". The roof thus represents a combination of normal and inverted roofs. Since the roof waterproofing is "packed" between two insulation layers, it is subject to less thermal stress. When renovating a normal roof in this way, it must always be ensured beforehand that the "old" roof has its full structural function and that there are no previous damages to the roof structure.