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Attachment joints

Keeping out sound and cold together

Windows and walls can have good heat and sound protection. However, it is the professional joining of both components that guarantees full functionality. A further challenge for planning and designing attachment joints: the trend for increasingly large windows. Over the course of time, the window attachment joint has developed from a simple seal with plaster to a high-tech connection.

The sealing systems of the joint technology play a significant role in determining the quality of the entire building construction. The challenge lies in using and combining the currently available product range of film, sealing material and foam correctly in accordance with the requirements stated. As various elements are usually involved at these joints, there must be unmistakeable clarification of who is responsible for which manufacturing area and any subsequent effects. The planner should specify all attachment joints, with an all-round representation of the adjacent components to a scale of at least 1:5, with all boundary conditions and dimensions.

With the aid of new testing methods, such as the blower door test and thermal imaging, it is now possible to also evaluate the actual quality of the various connection joints retrospectively.

Requirements for attachment joints

Requirements for attachment joints

The five "musts" of a good joint

  • Taking the thermal changes in an installation part into account, the blocking and mounting must function without any maintenance for the duration (30 years).
  • Any tolerances occurring must be compensated without weakening the sealing functions.
  • The heat and sound protection behaviour of the entire construction must not suffer any noticeable weakening due to the attachment joint.
  • The inside must be sufficiently sealed against air and vapour and the outside must be completely sealed against driving rain.
  • The installation must be organised such that any subsequent removal is possible without damaging the adjacent reveals.

Filling the joint gap

Filling the joint gap

Well insulated


The cavities in the attachment joints must be filled with insulating material. Mineral fibrous insulating materials or PU foam can be used for this purpose, either individually or in combination. However, PU foam must not be used as a means of attachment. The nominal joint width between the prepared reveal surface and the lateral surfaces of the block frame should be at least 1,5 cm. Low joint widths below 1 cm must be avoided, particularly for large windows. When filling the joint gap, the blocking of the block frame must not be removed. For sealing systems with wet grouting or compression strips, the joint filling must be removed accordingly.

Sealing the window

Sealing the window

Three sealing levels



The inner seal must be airtight all the way round and prevent the room air from penetrating the joint area. The attachment of a sealing film or sealing with permanently elastic sealants (e.g. silicone) ensures a fully functional seal.


Window level

The middle level of the attachment joint has to fulfil the requirements for heat and sound protection. It must be completely filled with insulating material (PU foam or mineral fibrous insulating materials). This level does not offer a seal against wind or moisture.



The outer seal must be impervious to wind and driving rain all the way round. It must be more permeable than the inner seal so that any moisture that does penetrate can escape outside.