Research results show that building materials which bind moist air - such as wood and wood-based materials - can have a considerable influence on the humidity in a room and its fluctuation. This phenomenon has several favourable effects on the quality of indoor air.

The results are based on the first and already completed stage of international research by the Technical Research Centre of Finland(VTT). The research will last many years, the second stage terminating at the beginning of next year. The parties involved in the project are the building and transport operating unit at VTT, the civil and environmental engineering department at Helsinki University of Technology and the German Fraunhofer Institut Bauphysik. The research is directed by a broad-based steering party consisting of industrial and financial representatives.

The research on indoor climate has brought a great deal of information in recent years about the direct and indirect effects of moisture on the quality of room air. These days we know very well in what range relative humidity should be and what the consequences are when you go outside the recommended range.

Structures make a difference

The variables showing the condition of indoor air are moisture content and temperature. Moisture is not a constant; it varies in spite of ventilation in rooms when the moisture output changes rapidly during the day. The cycle of changes depends principally on a person's actions. As far as the quality of room air and comfort are concerned, however, it would be best for the relative humidity to be kept as well and as long as possible within the recommended range.

The research shows that the variation in the relative humidity in room air can be affected by storing moisture temporarily in hygroscopes i.e. in breathing building materials. This being so, building materials and structures have a greater effect on reducing the fluctuation of moisture in the air than regulated ventilation. Structures also have a major role to play in keeping the room temperature steady within the desired range. Seen from this perspective, there is a very good case for using buildings materials that bind and release moisture and structural solutions that store heat.

Mould thrives on damp

High relative humidity in the air (above 60 per cent) combined with a relatively high temperature (more than 25 degrees) considerably reduces comfort and the feeling of cleanness and freshness in the air. This is particularly apparent during the summer: when you sleep, you feel sticky because the sweat does not evaporate adequately. Even completely clean air begins to feel stuffy.

Bacteria and viruses thrive in both low and high relative humidity, mould and dust mites in high relative humidity. Respiratory infections increase in dry air, allergic reactions and asthma in damp and dry air.

Advisors:
- Erkki Kokko, consultant in construction physics, Rakennusneuvonta Kokko Ky
- Pekka Nurro, Wood Focus Oy
- Keijo Kolu, UPM-Kymmene Puuteollisuus

UPM-Kymmene produces high-quality solutions for wood construction. House facades often utilize WISA-Pro panelling and WISA Special Plywood.
Photo: UPM-Kymmene