Why do attics have problems with moisture damage during winter?

  • Why do attics have problems with moisture damage during winter?

    There are several factors affecting the moisture ratio and climate in attics. A naturally ventilated attic is exposed to long periods of negative ventilation, which is ventilation that is not dehydrating but on the contrary moistens the attic space, especially during the winter months when the outdoor air has a low temperature and high relative humidity (RF%). Another contributing factor to high RF% is when warm humid air from the indoor environment finds its way into the attic, and together with the moisture in the air that is ventilated into the attic, you get problems with the moisture condensing inside the attic, especially at night when the roof goes through “undercooling” due to night radiation.

    Night radiation, a moisture problem?

    Night radiation is a phenomenon that occurs on clear cloudless winter nights when heat energy radiates from the earth into space, and all surfaces facing the night sky are cooled by the radiation exchange with space. This is why you sometimes have to scrape the windshield but not the side windows of the car. In the same way, roofs that cool down during cold and clear nights are affected; large temperature differences can occur between the roof and the ambient air, which increases the risk of condensation on the inside of the roof. When the warmer and more humid air in the attic then meets the cooled inside of the roof, condensation or frost is formed. The next day the temperature rises, causing the roof inside the attic to quickly rise in temperature as well. Combined with a high relative humidity, this creates a good breeding ground for microbial growth and mold.

    How to solve the problem of a damp attic

    • Seal the attic joists and ventilate the living area, not least the wet areas, to prevent the moisture in the air flowing into the attic area.
    • Install permanent equipment for controlled ventilation in the attic space. This creates a suitable environment for all building materials that prevents mould, rot and other microbial damage.
    Read more about dehumidification of attics »
  • 4 quick facts about attics

    1. Approx. 9 out of 10 small houses have a cold air, ventilated attic.
    2. Studies show that 72 % of all small houses with cold attics have an increased moisture ratio and a lavish presence of mould.
    3. In recent years Chalmers University of Technology and the the Royal Institute of Technology in Stockholm, have conducted several studies that have shown that moisture and mould in attics is a major and growing problem.
    4. Attic damage is rarely covered by standard house insurance, so it is recommended that the attic should be inspected once a year to be able to detect and rectify any damage.