Material Analysis and Indoor Chemistry

Research project

Development of a renovation technique for odorous older wooden houses through building physics and chemical-physics measures

In older wooden houses, strong, unpleasant odours sometimes occur which are characterised by the inhabitants as “mouldy” or “musty”. Our research results show that chloroanisoles are the principal cause for these odours. 

© Fraunhofer WKI
Schema zur Entstehung von Chloranisolen durch mikrobielle Umsetzung. Die Hauptreaktionswege sind rot dargestellt.
© Fraunhofer WKI
Verteilung der TeCA-Konzentrationen in der Wandluft eines betroffenen Gebäudes (Rot = sehr hohe Konzentrationen (> 100 µg/m³), Orange = hohe Konzentrationen (50-100 µg/m³), gelb = mittlere Konzentrationen (10 – 50 µg/m³), grün = geringe Mengen bzw. kein Nachweis (< 10 µg/m³)).

The investigations into the creation process showed that the development of the chloroanisoles, which are responsible for the odours, takes place in a secondary process (Fig. 1). Health impairments are, however, unknown and can be ruled out in accordance with the current level of information. In order to be able to offer a solution for the described problem, appropriate renovation techniques, which take into account building physics and chemical-physics aspects, should be developed within the framework of an AiF project. The objective of this now completed project was the development of more effective and more cost-efficient renovation measures which would enable the odour-free use of houses contaminated with chloroanisoles.

Within the framework of the project, samples of room air and or wall air were examined from a total of 15 buildings (39 rooms). This enabled a deeper understanding of the boundary parameters influencing the phenomenon. It was determined that, over long periods of time, pentachlorphenol escapes from the framework and is adsorbed by other spacing materials (sheeting, insulation material, fibre panels). Evaluations showed that material moisture levels can be reached which enable the development of chloroanisoles through microbial conversion to such an extent that micro-organisms are able to flourish. This occurs mainly in north, north-west and west-facing spaces, as these have the least opportunity of drying through sunshine (Fig. 2). The process can, however, spread further. In addition, the chloroanisoles spread through diffusion. The material moisture, which initiates the development of the chloroanisoles, does not lead to the growth of wood-destructing mould and does not physically damage the substance of the building.

Diverse approaches to a cure were followed, as it quickly became obvious that a rigid renovation process for all the affected houses was not the solution to the problem. On the contrary: a number of measures must be combined in order for the cause to be completely and permanently eliminated. Furthermore, it became obvious that individual alleviating measures must be defined which, whilst admittedly not combating the actual cause, nevertheless enable a cost-effective temporary improvement. Such measures include, for example, the installation of a ventilation unit which can later be integrated into a ventilation system within the framework of an overall concept. Alternatively or additionally, absorptive activated carbon wallpaper can be put up in order to temporarily reduce the concentration of chloroanisoles.

In addition to these interim solutions, various measures can be taken to intervene in the process. At the very least, the spaces should be opened, if possible from the outside, and the fibre boards removed and replaced. This also applies to insulation material and sheeting. The next step is to coat the framework with a pentachlorphenol-blocking layer, wherever possible. The reconstruction of the spaces should include an effective thermal insulation system which ensures permanent low moisture levels. The renovation can, depending on the location of the affected spaces and rooms, be carried out as part or complete renovation. Optionally, or depending on the odour burden, open areas such as electrical sockets can also be sealed. For the elimination of emissions from the remaining building components, activated carbon can be built into the spaces, e.g. in the insulation. In the rooms themselves, all adsorptive materials, in particular curtains, carpets, furniture, clothing, etc. should be replaced or thoroughly cleaned. In addition, chloroanisoles remaining in the room air can be removed through the application of wallpaper containing activated carbon. Irrespective of the composition of the respective chosen renovation technique, the measures must always be carried out meticulously and professionally, as improper workmanship and/or a combination with other measures can impair the effectiveness.


AiF, Industry