Does Mold Grow in Winter?

Why this question keeps coming up

People associate mold with July. January surprises them when the bedroom window grows black gaskets.

What it looks like in York County

Our winter radon piece explains the closed house. The same closed house puts shower moisture on single-pane glass and cold closets. Ice dams are the attic version, common after a freeze-thaw stretch.

What to do

• Wipe condensation and find why the glass is that cold or the room that wet.
• Run bath fans to the outside.
• Look in the attic after a damming winter.
• Keep a gauge downstairs anyway.

What makes it worse

• Assume the furnace “kills” mold.
• Seal a wet window with plastic and never look at the frame.
• Store wet firewood in the cellar all winter.

If the only winter clue is a sweaty radon pipe, that can just be cold plastic in humid air — wipe it and check the room gauge before you rebuild the system.

Questions people also ask

These pages are homeowner education from Radon Mitigation of York, written by Dave Kessler. They are not a medical diagnosis, a species identification, or an insurance determination. Color does not tell you which mold you have. If someone in the house is sick, talk to a physician. EPA's homeowner guidance treats roughly 10 square feet as the line where many people stop DIY cleanup and call a remediation crew — sooner if sewage, HVAC, or anyone immunocompromised is involved. We are a radon and basement crew. When we are already under a York house we will tell you what we see and what we would do in our own place. We do not pretend a radon fan is a mold remedy.