Leaky Windows Can Cause Moisture On Panes


November 16, 1991|By Karol V. Menzie and Randy Johnson

This year's prize for the most timely question goes to a reader in Chicago who wrote to ask what might be causing moisture to build up on the inside of the storm windows on the second floor of the house.

"The question that most often comes up," on the subject of indoor moisture control, "is, 'Why do I have moisture on my windows?' " says Gustin Kiffney, of Energyworks, an energy consulting firm in Baltimore. Condensation occurs when warm, moisture-carrying air hits a surface that is cold, impenetrable, and has enough "mass" to sustain the water.

In the case of storm windows and prime windows, as Mr. Kiffney explained it, moisture will gather on the surface that is colder than it should be. If the moisture is on the inside of the prime window, the storm window is not doing its job of providing "dead" air space, and is allowing cold air to get to the prime window.

In the reader's case, the moisture is condensing on the storm window, which means the inside window isn't doing its job. The moisture is behaving as if the prime window wasn't even there, condensing on the surface where warm air meets cold.

The solution is to make the prime window tighter, by weatherstripping, by adjusting the stops (wood strips that form channels for the sashes) and by making sure the sashes close completely, with a lock that works, to draw the sashes together tightly in the middle.

And it's possible there may simply be too much moisture in the house.

All kinds of sources introduce "pounds and pounds" of moisture into indoor air, Mr. Kiffney says, everything from having an uncovered dirt crawl space to making a lot of soup stock to "teenagers taking long showers." Wet basements and precipitation leaking from outside may be culprits, as may space heaters and badly maintained furnaces and water heaters.

While turning on ventilating fans and opening windows will work to make the house drier, you really need to control as many of the sources as possible.

Cover the dirt in the crawl space with 10-mil plastic; use vent fans with appliances and in bathrooms. Track down and eliminate the sources of basement water. (Make sure you try all of the simple solutions first, filling holes, adjusting slopes and providing drainage, before you escalate to expensive equipment.)

Precipitation leaks, Mr. Kiffney said, are almost always caused by bad soffits, loose shingles and missing drip edges that allow water to blow back up under roof edges.

Make sure water heaters and furnaces are drawing properly. If they're not, dismantle the flue and clean out the chimney.

One of the reasons this problem of indoor moisture comes up so often, Mr. Kiffney says, "is that people are generally moving from older houses heated with gas or oil to newer houses heated by heat pumps or electric heat. . . . Houses no longer have a chimney. A chimney is a big 8-inch hole through the roof that is constantly taking air out of your house. It's constantly ventilating your house as long as that furnace is running. So older houses with a fossil furnace -- oil or gas or wood -- are going to be drier than newer electric houses that don't have this hole in the roof."

Indoor humidity usually mimics outdoor humidity, he points out, so it will vary with season and temperature. There's no "ideal" amount of indoor moisture: at 20 percent, the air may feel dry and you may get sparks off objects you touch; at 50 percent, the air may feel damp.

There are dangers in using machines to humidify or dehumidify indoor air. Humidifiers can introduce biological pollutants -- molds, mildew and bacteria -- and dehumidifiers, which can cost upwards of $100 a year to run," are rarely capable of removing as much water as needed, at least not without near-constant supervision.

Moreover, the machines don't touch the real problem.

"What really makes a difference is source control," Mr. Kiffney says.

Next: Renovating for special needs.

Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is Home Editor of The Sun.

If you have questions, comments, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore, Md. 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.

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