I live in an old home with single pane windows. My house gets very humid 50-60% range and higher if I don't keep the home very cold. My hunch is that my windows are very leaky and the outdoor summer humidity is leaking into the house with the heat as well.

The reason I think the windows are the primary source of humidity is because the interior window has a LOT of condensation on the outside of the glass. The outside of the interior windows are also covered in mold and I have to clean them regularly.

I'm already planning on installing some stick on plastic insulation for all the panes as suggested in many other posts, but shouldn't my storm windows prevent the outside heat and condensation from reaching my interior window? I've seen on some youtube videos that there should be a gap at the bottom of a storm window to allow any drainage to leak out, but if that's the case then the window provides little insulating benefits?

Actually, now that I've looked outside at them I can see a few are well sealed all the way around, but perhaps it's just that the storm window is very old and its gaskets/seals/etc. have deteriorated.

Should I replace my storm windows? What should I look out for when replacing them? Any good guides to follow?

  • Seems like a good start inspectapedia.com/exterior/….
    – Breedly
    Aug 2, 2022 at 17:13
  • check this out energy.gov/energysaver/storm-windows
    – Traveler
    Aug 2, 2022 at 17:53
  • the colder you keep it inside your house, the higher the humidity will be inside your house. if you seal a ziplock bag at 50% humidity at 80F, dropping the temp to 65F will jack up the humidity in the bag tremendously. Your storm windows or lack thereof should be a minor factor in how humid your house is. Don't take my word though, try sealing one up with masking tape and see if that cuts the fog.
    – dandavis
    Aug 2, 2022 at 18:00
  • It sounds like your storm windows are working correctly. If they were too leaky, the inner pane would be warmed enough from outside air that it wouldn't condense. You storm windows are slowing down the temp transfer enough to allow the inner pane to stay cold, which is a good sign. Fogging would go down with more airflow, if that's what you want. If you want to seal them up enough to stop fogging, they will have to be basically hermetically sealed, which is not their intent. Your symptom points towards a house too cold or inner panes that are too thin.
    – dandavis
    Aug 2, 2022 at 18:07
  • 1
    The story of humidity. It is in the air therefore it is everywhere. You can not see it until it deposits on cold surface and creates drops. If you let the interior temperature rise to the outside temperature you will not see the drops. Every home has humidity, and uses different methods to deal with it. Most have Air conditioning, that remove humidity by the condensation method (converting the humid air into drops, by cold surface method. Some have de-humidifier that does the same. Seal your storm windows around the edges.
    – Traveler
    Aug 2, 2022 at 18:16

1 Answer 1


I think one of the main issues is that my windows aren't weatherized very well. So there's a lot of air leaking from the interior window to the exterior, as well as exterior air entering the house through the interior window.

I'm going to look at basic weatherizing with weather stripping and caulking as per How to install window weatherstripping

  • Rubber weatherstripping
  • Rope caulk for temporary sealant on areas that need movement.
  • Silicone caulk at joints that don't need movement.

This video from Home Depot also seems fairly good for finding leaks Weatherizing Doors and Windows: Overview | The Home Depot

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