ask This Old House
Vent for an upstairs dryer
Previous owners moved the laundry room to the second floor and terminated the dryer vent in the attic space above, since it’s not near an exterior wall. What’s the best way to vent it to the outside?
—NIKKIE COOPER, GIG HARBOR, WA
TOH plumbing and heating expert Richard Trethewey:
It’s become popular to put laundry rooms on the second floor for the convenience, but venting a clothes dryer into an attic is a big mistake. Warm, moist air from the vent creates a perfect climate for mold to grow on the roof framing, sheathing, and anything you’ve stored in the space. In cooler weather, that damp air will condense on cold surfaces, soaking insulation and possibly damaging the ceiling below. And in snowy climates, all that extra warmth contributes to the formation of ice dams.
To avoid these problems, consider the most direct route to the outside—through the roof. In that case, you’ll need to connect the ductwork to a hooded roof vent that offers minimal resistance to airflow from the dryer (see “Better Exhaust Vent”).
Installing such a vent, even on an asphaltshingled roof with a low slope, is best left to a roofing pro with proper fall-protection equipment and who knows how to properly flash around roof penetrations.
Once the vent is). Then wrap the metal with R-8 duct insulation to minimize internal condensation.
