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Window Moisture

My wife and I recently bought our first house. It is a circa 1900’s farmhouse in the Annapolis Valley in Nova Scotia. We got it for a pretty good price so we overlooked some of the apparent flaws that it had. Some of the flaws have come back to haunt us by letting in more cold air than we had anticipated.

I thought that the windows were a plus. They are modern replacement windows that were manufactured in 1983. Unfortunately they have been letting in a lot of cold air. The windows are all double-glazed, but five of them have condensation that is between the glass. There is evidence of water damage both on the wood casings (surrounding the glass) and in between the plates of glass themselves. The wood that is at the bottom of the top window pane is black with mildew. The wood is sound, it is just damp and discolored. The caulking around all of the panes of glass has mildew on it. We don’t understand why, all of the windows are double-paned and we figured this type of setup would have been the most weather resistant.

The house has vinyl siding and a dirt floor basement with rock walls. It gets quite damp down there in certain spots when it rains. It isn’t insulated. I haven’t properly vented our dryer yet. The vent goes into the basement. There is no bathroom vent. — Jay & Heather Stirling

Too many double-paned windows, also called “insulating glass”, are failing after just five to ten years in service. The seal at the edge of the glass fails and moisture enters fogging the glass. The only solution is to replace the glass. In your case you may need to replace the entire window unit to solve the air infiltration problems. The window replacement industry is highly competitive so you get what you pay for. The best quality windows are usually the most costly. However, recent studies indicate that even the best insulating glass units may fail after ten to fifteen years. I am beginning to think traditional single-pane window systems may be better in the long run.

The moisture is rising up from your cellar and condensing on the interior side of the windows where it soaks into the putty and dribbles down to deteriorate the wood at the lower rails of the sash. You are correct be concerned about this moisture at the windows because it is an indication that moisture is also condensing within the walls where it becomes trapped by insulation and the exterior vinyl siding. This could be causing a much greater hidden problem than the relatively minor window deterioration you see.

Begin by controlling and reducing the moisture in the cellar. You already know you must vent the clothes-drier outdoors and install vents in all kitchens and bathrooms. These are the obvious sources of moisture, but the cellar’s dirt floor and stone walls may be generating much more moisture. Look for the sources of this additional moisture. Most likely it is due to poor drainage around the foundation exterior. Downspouts may pour water out right at the foundation. Fix the downspouts with ground leaders to channel the water 5-10 feet away from the foundation. The ground may slope toward the foundation and let water flow down into the foundation walls. Regrade the ground for 5-10 feet away from the foundation with a 1-2 inch drop per foot of run. After you have done this wait for a couple of years to see if this reduces the moisture in the cellar and house, if not ground water may be coming up from beneath the dirt floor by capillary action or as water vapor. This is more difficult to deal with. Possible solutions include ventilation of the cellar to the outdoors, and extensive interior drainage systems.

John Leeke is a preservation consultant who helps homeowners, contractors and architects understand and maintain their historic buildings. You can contact him at 26 Higgins St., Portland, Maine, 04103; or by E-mail:; or log onto his website at:

© John Leeke

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