Thomas Runzheimer
Bibliographic info:
9th International BUILDAIR Symposium, 8-9 May 2015 Kassel, Germany

Purpose of the work

Many top-floor apartments and single-family homes from the ’80s and ’90s had been insulated in the roof area using aluminum-clad panels or PE foils and had frequently been covered with profiled wood. These buildings suffer from a significant lack of airtightness that can be retrofitted from the inside with a high technical quality. The improvement in airtightness achieved by this approach in most cases shows better results than a retrofit from the outside.

Method of approach

A retrofit usually provides a good level of airtightness when the existing insulation layers are dismantled and the airtight layer is completely renewed. Difficulties in the implementation frequently occur in the area of badly accessible connections and penetrations, and of the existing installations. In addition, the existing sub-surfaces often require specific measures in order to create a new airtight layer.

Content of the presentation

The presentation shows several practical implementations of roof retrofitting and detailed solutions as well as a number of constructional difficulties encountered in their realization. It will also analyze the results from the airtightness test and provide the costs of the measures.

Results and assessment

Roof retrofitting from the inside achieves comparatively good results if the airtight layer has been planned and implemented in a simple and logical manner. In comparison to retrofits from the outside, it is beneficial that the airtightness can be tested throughout the construction process and errors can be remedied in a targeted manner. The stress on the airtight layer caused by climate conditions and construction activities can also be kept at a significantly lower level when retrofitting from the inside.


If the roofing of the structure still offers sufficient useful life and there is a conclusive way of insulating the interior of the attic floor, retrofitting from the inside should be given preference over retrofits from the outside. Independent of a total retrofit of the building, the energy consumption of particularly air-permeable top-floor apartments can be significantly reduced while the level of comfort increases.


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