Condensation Problems in Attics


Attic condensation occurs more during the winter months when your house is more closed up and airtight. It can lead to structural damage to the trusses and rafters and decreases the effectiveness of insulation. Attic condensation also has the potential to cause ice dams on the roof, which can lead to water damage in your home.


  • During winter when heating the house, moisture from the main house flows into the unheated attic and causes condensation. This warmed air also raises the temperature in the attic and, if it reaches over 32 degrees, snow on the roof begins to melt and run off the roof. When the melting snow reaches the cooler area of the roof, it freezes and becomes ice. The proper amount of insulation in the attic addresses these temperature fluctuations and prevents heat from escaping and condensation from forming.


  • Heat rises and flows into the attic through passageways and bypasses where it is trapped as water vapor that condenses on surfaces in the attic. As temperatures fluctuate in the attic, the water vapor goes through a freeze/thaw cycle that contributes to humidity problems in the house. Excess humidity in the house potentially causes damage to ceilings and walls. Bypasses and passageways into the attic include spaces around the chimney and plumbing fixtures, along with areas around light fixtures and up interior walls.

Preventing Condensation

  • Proper attic ventilation is crucial to condensation prevention. In an attic ventilation system, fresh, cool air is drawn in through vents in the eaves or soffits. Hot, moist air is then expelled at the top of the attic through roof ridge or gable vents. Some vents include fans that help move the warm air, particularly in houses without eaves in which to install intake vents. Create a good air barrier between the attic and the main house by sealing around attic penetrations such as areas around electrical wiring, plumbing pipes and chimney chaseways.

Decreases Moisture Levels

  • Never vent a clothes dryer to anywhere other than outdoors. Store firewood outdoors; even what appears to be dry firewood may contain enough moisture content to raise levels in the home. Run a humidifier only if absolutely necessary, and consider the type that are controlled by a humidistat to maintain acceptable levels. If water condenses on windows, especially after showering or cooking, crack a window to release excess moisture from the air. By decreasing moisture levels, less water vapor escapes into the attic to form condensation.

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