How to stop condensation in a loft

Updated February 21, 2017

Due to the position of the loft at the top of your house, moist air from below can seep into the space and condense underneath the roof. Unfortunately, this condensation can lead to mould and mildew growth, wood rot, insect infestation, and warped loft floors. There are, however, steps you can take to stop condensation in your loft.

Increase ventilation in the loft. For proper ventilation, lofts and attics require 30 cm (1 foot) square of unobstructed ventilation area for each 46 metres (150 feet) square of loft area. Common loft and attic vent types include eave, gable, turbine, roof and continuous ridge.

Increase circulation. Circulation and ventilation go hand-in-hand. To increase circulation in your loft, consider running an attic fan. You should also consider installing an exhaust fan in areas of your house where moisture is high, such as bathrooms, utility rooms and kitchens.

Seal cracks in the loft. Condensation will occur in your loft if moist air is leaking into the loft. Check the areas where the wall meets the floor and ceiling, and make sure that any soil and vent pipes that pass through the roof space are sealed. In addition, if you have a loft trap door, make sure the lid sits firmly on a draught excluder or rubber beading.

Reduce moisture in your home. To reduce the moisture in the air of your home, consider running an air conditioner during the warm months and a dehumidifier during the cold months. Keep the relative humidity in your home between 30 and 50 per cent to avoid problematic condensation. You can buy a relative humidity gauge at your local DIY shop.

Install skylight windows in the loft. Windows create a buffer between the cold air outside and the warmer air inside, thus reducing the chance of condensation. This is important because condensation on the surface of loft windows can damage the walls and ceilings around the window.

Things You'll Need

  • Vents
  • Fan
  • Dehumidifier
  • Air conditioner
  • Relative humidity gauge
  • Skylight windows
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About the Author

Thomas King is a graduate of the University of Pittsburgh School of Law where he served as managing editor of the "Pittsburgh Journal of Environmental and Public Health Law." He currently lives in Aberdeen, Washington where he writes and practices law.