Climate

Interior Humidity and Condensation

If condensation appears on any interior surfaces, or on the inside of windows, doors or their frames it is an indication of a combination of high humidity within the home combined with low outside temperatures and inadequate insulation between the two. Condensation can lead to water damage to the trim, drywall, window coverings and can manifest as mold, mildew, stains and even dry rot.

Image showing condensation on the outside of cold water glass
Sweaty water glass condensation

Since you have no control over outside air temperatures, resolving condensation problems will usually mean dealing with humidity on the interior of the home and/or improving insulation. The first things to do are: 1) measure and learn the actual level of humidity that is in the home and 2) find out how well your home is insulated. Once you know these facts you can implement a remediation plan.

If the air in your home tests above 40% humidity, you will need to find a way to reduce that level. One way to lower humidity levels on the interior is to reduce the creation of steam. Shorter showers, fewer baths, less boiling water. Another approach is mechanical, such as installing and using strong exhaust fans in moisture producing areas or a mechanical de-humidifier can also be installed.

The other part of the condensation equation is insulation. First test to see if there is adequate insulation in the walls or if any of the stud bays are missing insulation. This can be checked with by an inspector with and infra-red camera. Poor insulation often occurs in walls and around outlets and switches.

Uninsulated windows will also allow condensation to form as will some metal frames around windows and doors. These shortcomings will need to be corrected in order to stop the condensation problems. To prevent condensation, the correct minimum insulation R-value for the walls and windows will need to be enough to prevent the dew point from being reached on the interior surfaces.

To-Do

  • On a cold day in winter, check the window panes and frame in your home for condensation.
  • Check your exhaust fans and make sure they are clean and functioning properly.
  • Consider adding exhaust fans if the condensation persists

Maintenance

  • 1x per year: Check and clean all the exhaust fans in the home. Remove the covers and clean off any dust build up. Clean the fan blades, clean them and observe them operating to make certain they are working properly.

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