A warm roof promises thermal protection and heating energy savings

The warm roof is classically used for flat roofs. In contrast to the cold or double-skin roof, there is no air gap here where the moisture diffused through the ceiling can escape to the outside. This makes it necessary to use an appropriate construction method to ensure that any moisture does not damage the roof structure. In the past, there were no really appealing solutions for this – the cold roof was considered a more attractive method. Nowadays, modern building materials and house ventilation systems can put a stop to the moisture problem, which means that the warm roof is often used.

The structure of a warm roof

In a warm roof, all the layers lie directly on the supporting ceiling. The absence of an air space makes a vapor barrier in front of the insulation layer indispensable. In order to efficiently maintain the entire house insulation, the insulation layer must not become damp under any circumstances. If the water vapor were to diffuse through diffusion-open building materials, for example, it would condense at the point where the material temperature is lower than the dew point, and the roof structure would become damp – mold or even water damage would be the result, and the warm roof would fail to perform its entire function, i.e. house insulation, since moisture massively reduces the heat-insulating effect. You may also need to install snow guards for your roof.

The construction of a warm roof is classically carried out from the inside to the outside as follows:

  • A supporting structure (in the case of a flat roof) made of reinforced concrete, for example, assumes the task of bearing loads of the overlying roof structure in addition to the obvious room-dividing function, and furthermore also ensures sound and fire protection. The slope of at least two percent prescribed for flat roofs can be created here using appropriate sloping concrete.

  • This is followed by a leveling layer. This mainly acts as a separating layer for incompatible materials.

  • This is followed by the vapor barrier. This is a barrier for moisture-enriched air and prevents the penetration of the warm roof by the same. Mostly polyethylene foils are recommended for this purpose.

  • The thermal insulation follows directly and, depending on the processing, can also be used to create a slope. For the warm roof, mineral fiber materials such as rock or glass wool, rigid polystyrene foam panels or foam glass are particularly suitable materials.

  • As a rule, a so-called vapor pressure equalization layer is applied to the thermal insulation. This ensures that the vapor pressure generated when trapped moisture heats up is distributed and thus relieved. Furthermore, relative movements between the waterproofing and the thermal insulation are made possible.

  • The subsequent waterproofing serves to make the roof structure watertight from the outside. This is typically done using bitumen membranes or foil waterproofing.

  • A top layer of gravel, sheeting, slate chippings, ceramic interspersing or even a green roof substrate completes the warm roof. This layer protects the roof structure from direct sunlight, wind suction or mechanical damage.

A variant of the warm roof is the so-called inverted roof. As a flat roof, the thermal insulation is located above the waterproofing. The latter is thus in an average constant temperature zone all year round. However, liquid can enter the insulation layer unhindered from the outside, which deteriorates the house insulation considerably. Drainage in particular thus places special demands on the inverted roof – in modern installations, a water drainage system is found above the insulation.

The advantages and disadvantages of a warm roof

Warm roofs follow the trend of environmentally conscious construction in low-energy and passive houses. Due to completely closed roof construction, there are no thermal bridges through which the heat is dissipated. They are available in all imaginable sizes and shapes for almost any construction method. Compared to the double-skin roof, the average consumption of materials is lower and there is more space for the installation of the thermal insulation layer.

However, the room temperature of a house with a warm roof in the summer is usually higher than that of a building with a cold roof. The ventilation zone between the roof surface and the insulation layer of a cold roof causes thermal decoupling – the house virtually shades itself. The insulation thus has to regulate a smaller temperature difference and the house remains cooler in summer.

Furthermore, a house with a warm roof should, as mentioned at the beginning, have suitable ventilation, through which the resulting humidity can be removed. While this is superficially contradictory to the actual operation of a warm roof, the indoor humidity must be regulated in a controlled manner so that the water does not condense and you have to deal with mold. A high-pressure washer will help you remove the mold. It is an indispensable aid for keeping your home clean also you can get spray foam insulation washington dc done.


Warm roofs are nowadays the recognized state of the art. Problematic moisture courses in the roof and the location of the dew point can be regulated by modern building materials and clever house ventilation systems.