Q&A: How can I stop mold from growing on the bottom of the interior window frames in my two year old seasonal cottage?

Q: How can I stop mold from growing on the bottom of the interior window frames in my two year old seasonal cottage? It sits unused during winter, heated to about 5ºC. We keep curtains closed for security and leave ceiling fans running. I’m worried that the problem comes from the fact that the building was constructed up in winter, and the wood might have been wet.

 A: Let me start by putting your mind at ease. There’s nothing about the wetness of the wood used to build your cottage that would lead to long-term mold growth. Winter construction happens successfully all the time. That said, the solution for mold control is always the same: moisture control. Every house is made at least in part with mold food. That is to say wood, drywall, carpet, wallpaper – all these materials are prime surfaces on which mold can thrive when conditions are right. The only factor we can control is moisture. Make a surface dry enough, and mold can’t grow, even on the most mold-friendly materials.

This very quiet, very powerful Panasonic fan is being installed as part of new bathroom construction. Ventilation is one tool for preventing mold growth.

So the solution in your case is to lower indoor humidity levels, especially during those months when you’re not at the cottage. I suspect that liquid condensation is developing on your windows during cold weather, then running down the glass and triggering mold growth. The good news is that the colder the weather outside, the drier that outdoor air will become when you bring it indoors and heat it a little. Do you have exhaust fans at your place?

Need help choosing a fan? According to SplendidFans.com, today’s best exhaust fans use very little electricity, and can be hooked up to variable speed dial control. Even a very slow but constant fan speed will make a big difference in your case. Leaving the curtains open will also reduce the tendency for condensation to develop on windows.

This variable speed control allows exhaust fan operation to vary from full throttle to barely moving. Controls like this are useful for slowing fans down for long-term, background ventilation.