Roof Vents and Carpet Glue

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Q We recently had a new roof put on our house. The contractor told us that our old ridge and soffit vents were not up to code, and he redid them. What's the purpose of these vents, and why are they so important?

- R.A., Lexington, Mass.

A This question is best answered by the following illustration, says Howard Clark, a general contractor in Holliston, Mass. Inflate a balloon to its maximum size, tie it closed, stick it in the freezer, and then check on it later. The balloon will have shrunk, and you'll find moisture inside the balloon. Why? Because the energy of the air molecules is wilting under the effects of the freezer, and losing the ability to support water vapor. Thus, the water condenses on the inner surface of the balloon.

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Now consider your home as a giant balloon that your family is constantly inflating, and that Old Man Winter is the icebox. Consider also that, even though we insulate our ceilings, mechanically heated air, laden with moisture from cooking and plumbing conveniences, seeps up past ceiling layers to touch the roof. Like the skin of the balloon, the cold underside of the roof collects moisture, but unlike the balloon, this surface is absorbent. Very quickly the attic would become soaked. This condensed vapor will actually drip and puddle. It rots out sheathing and rafters, ruins insulation, and soaks and stains framing, drywall, and plaster, where it supports mildew and house-eating pests.

Good attic ventilation totally neutralizes this problem. Soffit vents work in conjunction with gable vents or ridge vents. They spread large volumes of drying air evenly through the attic to carry off moisture. This means the attic should be about the same temperature as the outdoors. By code, contemporary homes should have one square foot of free ventilation for every 300 square feet of ceiling space, and older homes should have twice that; one square foot free ventilation area for 150 square feet of ceiling.

Q We removed old outdoor carpeting from our patio that has been there 30 years. The carpet is gone but not the glue, which is too soft to sand off. How can we remove the glue?

- T.S., via e-mail

A It depends on the type of glue. You may need to experiment on a small area, says Dan Priest of the National Association of Home Builders. If it's latex glue, it should be water soluble, so you can use a product recommended by a hardware store. If that doesn't work, you can try sandblasting (equipment can be rented) or pour a new surface of concrete over the top.

John Nelligan of Home Depot in West Roxbury, Mass., has an alternative: scraping off the residue. He recommends a scraping bar, which looks like an ice scraper but is wider. Look for it in the ceramic-tile aisle.

Readers: Pose your questions and we'll seek out experts on home repairs, gardens, food, and family legal issues. Send queries to the Homefront Editor, The Christian Science Monitor, One Norway Street, Boston, MA 02115 or e-mail home@csps.com

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