Window condensation on interior glass surfaces—not in between thermal panes—can pose problems for home owners if not addressed properly. Many modern log homes feature large expanses of windows as part of their design, so we decided to take a look at what can be done.

Condensation occurs on the inside of windows when the interior humidity reaches a certain level in conjunction with the outside temperature. Windows themselves do not create moisture, they respond to their environment. Condensation can become an issue during colder months, especially as the differences between indoor and outdoor temperature increase. Additional moisture and condensation can lead to costly mold or rot in window frames.

The configuration of windows can also play a role in interior condensation. The more glazing in your windows, the better the protection you’ll have from condensation. Triple glazed, low-E windows with argon gas fill are the least susceptible to condensation; single glazed windows are most likely to have moisture condense on them. For example, at 20 degrees Fahrenheit outdoors, a double-glazed window will begin to show inside condensation when the humidity level is 70%, but a single pane glass will evidence condensation at 20% humidity. Also a factor in preventing condensation is the overall U-factor of the window units. High U-factor frames will conduct the cold into the interior surface of the window, causing humidity to condense.

Regulating the interior humidity in your home is the key to minimizing condensation on windows. Interior humidity might become elevated during colder months when HVAC system humidifiers are not adjusted at the change of season. Other homeowners turn to humidifiers and vaporizers in colder months to increase human comfort indoors. The trick is to balance comfort with humidity to avoid window condensation.

There are many areas in the home, which can add to humidity levels indoors. Check clothes dryers and stove vents to ensure they are functioning properly. Turn on bath and shower exhaust vents when bathing to evacuate the excess moisture. Try to keep interior humidity to around between 40-50% to keep most modern double glazed windows moisture free. One way to minimize the effect of condensation in your new home is to select windows with an NFRC condensation resistance rating between 0 and 100. The higher the rating number, the more resistance that particular window will have to moisture condensation.