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18.10.2005

A VTT method to evaluate the moisture buffering properties of building materials
New selling arguments for Finnish companies on the European construction markets: New wooden structures to maintain comfortable indoor humidity

VTT has developed an experimental method to determine the properties of structures to even out indoor humidity variations. The method will enable companies to develop new wall and ceiling structures and material applications to make it easier to maintain indoor humidity at comfortably constant levels. Wood as interior sheathing material is particularly good for ensuring comfortable indoor humidity conditions. In continental Europe the widespread use of natural and window ventilation sets requirements for passive structural means to produce comfortable indoor conditions. The new wooden structures should provide Finnish companies with a competitive advantage to enhance the maintenance of good indoor conditions.

Constant heat and humidity levels are among the prerequisites of a pleasant indoor climate. The variations of the indoor humidity can be evened out by the correct choice of structures and construction materials, as research has demonstrated. Reducing the extremes in indoor air (very damp - very dry) contributes much to a comfortable indoor climate. The presence of people in the room increases the humidity load in a room. This generally varies depending on the time of day, and the humidity level of indoor air depends among other things on the outdoor conditions. The advantages of the moisture buffering effect that can be used to reduce the humidity variations of indoor air are most obvious in the dry winter and warm and humid summer seasons, when the indoor conditions may occasionally be outside the comfort zone.

Several construction materials and products may serve as moisture buffering layers. For example, an untreated or correctly treated wooden wall or ceiling structure can absorb humidity from the indoor air during occupation and release it back in the indoor air when the indoor humidity is lower.

Moisture buffering material layers should be in contact with or very close to indoor air. An air or vapour barrier outside the moisture buffering layer does not restrict the exploitation of the phenomenon. Taking advantage of the moisture buffering effect does not affect the moisture safety or structures. In addition, the improved indoor comfort may reduce the need for additional ventilation thereby conserving energy.

Humidity control of indoor air should be included in normal design practice, since maintaining comfortable indoor conditions is one of the main performance requirements of a building. This can be achieved by combining moisture buffering structures with well controlled ventilation.

The research was carried out by VTT and Helsinki University of Technology. A Nordtest standard defining the moisture buffering effect and test method will be presented as a result of a Nordic collaboration project. The research was funded by VTT, Woodfocus Finland and Tekes (The National Technology Agency of Finland).

Further information:

VTT Building and Transport
Tuomo Ojanen, Senior Research Scientist
Tel. +358 20 722 4743
tuomo.ojanen@vtt.fi
Woodfocus Finland
Pekka Nurro, Project Manager
Tel. +358 9 6865 4514
pekka.nurro@woodfocus.fi

Feel free to use all news. Photographs copyright Kalle Heiska.
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