Roof Vents Cut Dampness, Heat
QUESTION: I’m having my attic insulated by a local contractor. When explaining the job to me, he said he would need to add vents to the roof. Why is this necessary and where do they go?
ANSWER: Adding roof vents is important for roof integrity. Without them roof timbers can rot and composition shingles can start to curl. Roof vents do two important things--they remove unwanted moisture which can condense on the underside of the sheathing in winter, leading to rot. And they prevent high temperatures from building up in the summer which shortens the life of composition shingles.
To ensure adequate ventilation, vents should be placed high and low on the roof. Vent area should equal one square foot of free flowing area for every 300 square feet of attic area. The best way to install the venting is with one-half the vent area high in the roof, preferably along the ridge, and one-half low in the roof--within three feet of the eaves. High and low placement of the vents will encourage air flow along the underside of the roof sheathing--air enters the attic through the low vents and exits through the high vents.
Recent research suggests that the best protection against moisture condensation in the attic is to prevent its entry in the first place. The best way to do this is to seal all openings between the heated house and the unheated attic. These include light fixtures, plumbing penetrations, chimneys and joints between the ceiling and walls. Use caulking, weatherstripping, foam sealant or any material which will stop air flow that carries the moisture into the attic.
Venting Dryer Into Crawl Space Not Good
Q: I read with great interest (and some alarm) your recent article that clothes dryers should be vented to the outside and not the garage. The vent from my clothes dryer is a long one. It goes from the dryer down into the crawl space and then across the crawl space to an outside outlet. Due to the distance involved, there are two sections of vent hose coupled together. Recently, I noticed these sections had decoupled, venting heat from the dryer into the crawl space.
I decided to leave the situation as is figuring that the heat from the dryer vent would reduce moisture problems in the crawl space. But after reading your warnings about moisture build up, mold and mildew growth and, in a worst case, dry rot of wood framing materials, I’m concerned. Should I recouple the two sections of hose or is there enough air coming through the crawl-space vents to prevent any problems?
A: You are right to be concerned. Garages aren’t the only places that dryers should not be vented. Add to the list crawl spaces, basements, attics or any enclosed space where moisture and lint can build up. Dryer exhaust, though hot, is full of moisture and will only add to the moisture already present in your crawl space. The crawl-space vents are designed to carry moisture from the soil to the outdoors, but may not be adequate to exhaust the additional moisture provided by the dryer.
We recommend reconnecting the two pieces of dryer vent hose right away. For a long-term solution, you ought to consider venting to a location that is closer to the dryer. A shorter vent run will make it easier on the dryer motor to exhaust moisture and lint. It also ensures that most of it gets exhausted to the outdoors rather than condensing or building up in the hose.
Lint buildup can cause blockage at joints in the vent hose and, if it builds up in the dryer itself, can cause a small fire. If a closer location isn’t possible, check the vent hose regularly to prevent blockage from occurring.
Window Moisture May Need Resealing
Q: About five years ago, I replaced my single pane windows with insulated glass units. I’ve been generally pleased with their performance--the windows make the house more comfortable and the weeping window problem has disappeared. Recently I’ve noticed that a little bit of moisture builds up between the panes. It’s there in the morning, then dries up when the sun comes out. Why is this and what can I do about it?
A: Ideally, double pane windows would never leak, but unfortunately in the real world they occasionally do. The materials used to seal the two panes form an airtight seal when new, but as they age tiny leaks may develop. Likely causes include possible uneven settling of the separate panes of glass as well as environmental degradation from wind, rain and thermal stress.
In your situation it sounds as if the problem is only beginning to occur. Is your window still under warranty? If so, you may be able to have it replaced for a labor charge only. If not, to prevent worsening of the leak you could try caulking around the window edges in hope of sealing the leak. A better solution requiring more effort would be to remove the glass and reseal the edges completely.
Talk to several window manufacturers or contractors regarding a proper sealant for this job. When you replace the unit, make sure both glazing surfaces are supported on blocks so uneven settling will not occur. If the problem worsens, your only recourse may be to have the glass replaced. We recommend at least a 10-year warranty on seal leakage that covers both material and installation fees.
