Effectively avoiding thermal gaps in the facade

Kleines, gelbe Holzhaus steht auf einem Heizkörper und um das Haus ist ein Wollschal gelegt

With an external thermal insulation composite system (ETICS), buildings get a reliably warming envelope. Whether it is a new building or a renovation: a properly installed ETICS significantly increases the energy efficiency of a house. When installing the system, it is important to ensure an expert-like execution so that no thermal bridges will occur. Otherwise, these can cause damage to the building in the long term and drive up energy costs unnecessarily. The typical problem areas for thermal gaps are window or door areas, as well as the transitions to awnings or blind boxes. We show how these areas can be almost completely avoided by modern ETICS elements.

What are thermal gaps?

A thermal bridge, as the name suggests, conducts heat either from the inside to the outside or the other way round. This must be avoided as a matter of urgency, as otherwise expensive energy is lost for heating or cooling the interior in winter and summer. Thermal gaps often occur specifically at points on the facade where building elements are very close to each another, for ex. at areas with windows, doors or socket parts. Thermal bridges cannot be detected with the naked eye. However, thermal gaps can be easily detected with a thermographic camera (see picture below). The reason is that heat is conducted to the outside via thermal gaps, resulting in unwanted heat loss and thus in rising energy costs.

How are thermal gaps measured?

The U-value (also heat transfer coefficient) is a unit of measurement to indicate the heat loss of a building component. The higher the U-value, the worse the insulating effect. The German Energy Saving Ordinance (EnEV) specifies a maximum U-value for all building components of a house and thus determines the maximum amount of heat a house may lose. It applies to all renovation measures, with the exception of listed buildings. For an insulated facade, the EnEV prescribes a U-value of maximum of 0.24 W/(m²K). The U-value of an uninsulated exterior wall is - depending on the type of masonry and thickness - approx. 1.6 W/(m²K). The use of an insulating material reduces the U-value. The higher the insulation thickness, the lower the U-value.

Energy saving with ETICS

On the surface, an external thermal insulation composite system (ETICS) is a simple construction. An insulating shell of, for example, mineral wool or other insulating materials is applied to the existing masonry. ETICS are available in different variants. All of them enable a wall construction that contributes to the energy efficiency of the building. The way it works is similar to a thermos flask: in summer, a building envelope with thermal insulation protects the interior from overheating, and in winter, it protects against heat loss from the inside of the building to the outside. All components of an ETICS must be matched to each other so that there are as few thermal bridges as possible on the facade. Thus, insulation supports sustainable energy use and prevents unnecessarily rising energy costs. Especially in view of rising energy prices, the limited natural resources and, last but not least, CO2 emissions of energy production, it makes sense to invest in an ETICS.

Modern ETIC systems meet a high-quality standard and already offer high efficiency. Of course, there are differences in the insulation material. The decisive factor for the evaluation of insulation materials is the thermal conductivity λ [W/mK]. The lower the λ value, the better the insulating capacity. However, there are other criteria for the right choice of insulation material: class of reaction to fire, compressive strength, water absorption, sustainability or energy consumption.

Ready for low-temperature flow?

Gas or oil heating systems may no longer be installed in Germany from as early as 2024 in order to achieve the climate targets. In existing buildings in particular, however, simply replacing the heating system is not enough. Existing buildings must first be upgraded with facade insulation.

An insulated building envelope is a prerequisite for a heating system with a low-temperature flow. With so-called low-temperature, the heating water is heated to about 45 °C. This is much lower than with traditional heating systems in uninsulated buildings, which require heating water with temperatures of over 70 °C. So, anyone thinking about buying a heat pump should check in advance whether and to what extent the facades are sufficiently insulated. Otherwise, the benefits of climate-neutral heating systems for the residents, the wallet and the environment will be lost.

Why do thermal bridges occur more frequently with add-on components?

The connection of ETICS to windows or doors is technically more challenging, as it usually involves corners, edges and transitions from one element to the next. Here, even professionals need experience. When installing windows or associated elements, such as awnings, railings, external venetian blinds and window sills, improvised fastening options such as metal brackets are sometimes used in everyday construction work. However, metal has a fatal effect on the thermal conductivity of a facade. Apart from the fact that this does not correspond to the current state of the art, such improvised installations often lead to thermal bridges and, in the worst case, to defects in the building substance. Defects in the building substance, in turn, can cause moisture to penetrate the insulation level. Since damp insulation material does not provide heat, the damage then has to be repaired in a costly and time-consuming manner.

The way to reduce thermal bridges

Ideally, thermal bridges are directly prevented in the construction of a new building. In existing buildings, they can be reduced by retrofitting the facade. Whether for new construction or renovation, special attention is paid to the integration of add-on parts, such as windows, doors and awnings. For this purpose, innovative solutions have recently become available, ranging from mounting brackets to prefabricated elements with air exchange isolation or heat-insulating properties, which simplify the connection to the ETICS at the highest technical level.

Since 2021 the German Association for Insulation Systems, Plaster and Mortar (VDPM) describes a safe solution for the correct installation of add-on parts. Its technical sheet "Formation of details with profiles and joint sealing tapes in exterior renderings and ETICS" provides general information on planning, installation and maintenance in addition to the requirements for profiles.

Reliable waterproofing of building parts

Opening connections, such as doors, windows and window sills, but also critical areas like ETICS on the socket parts, must be tight. This is the only way to prevent the formation of thermal gaps. In addition, this also prevents the penetration of moisture.

A highly flexible universal waterproofing has proven to be a safe and practical solution. The universal waterproofing is applied up to approx. 5 cm above ground level and can then be covered with a facade paint or a suitable render. Important to note: the waterproofing is applied in at least two layers. In addition, the product is also suitable for bonding the insulation boards.


The efficiency of an external thermal insulation composite system is unnecessarily minimized by thermal bridges on adjacent building parts. Therefore, it is important to prevent thermal bridges. Improvised solutions for connecting these building parts (e.g. windows or doors) are not advisable, as they tend to exacerbate the problem.

Alternative systems including insulation or air exchange isolation can be easily installed on-site. This ensures efficient thermal insulation, and building owners enjoy cosy warmth in winter without unnecessarily high costs for heating.