Can a Bathroom Fan Exhaust Into An Attic?
After I became a home inspector, I inspected my own home. Even though I’m a handy-man, I noticed several things that needed to be fixed. As I was inspecting the attic, I noticed a black area on the attic sheathing and on a rafter. I crawled over to the area to get a closer look. The bathroom exhaust vent pipe was a flexible pipe made of plastic. A nail driven through the rafter had punctured the vent pipe.
The person who installed the vent pipe probably noticed the nail, but thought, “It won’t puncture the pipe” or “one little hole won’t matter”. But the nail did puncture the pipe. The hole grew to be the size of a penny. Warm moist air from the bathroom condensed on the attic rafter and the attic sheathing. "Mold" (or more likely mildew) grew on the rafter and the sheathing.
I have since removed the nail, replaced the vent pipe, and used bleach to kill the mold.
When a kitchen or bathroom exhausts directly into the attic it can damage the attic. In my case, mold growing on the attic rafter and the sheathing were the result. Such biological growth will eventually soften the wood and damage the roof structure. Not to mention that mold and mildew can cause health problems. Moisture can also condense in the insulation, making the insulation less effective.
It is best for kitchen and bathroom exhausts to terminate outside: through the roof, or through an outside wall.
During the real estate boom, many people bought homes without an inspection. Many homes have been owned for many years since an inspection was done. A home inspection can identify problems that would otherwise result in much greater expenses later.
SOURCES:
A Brief Guide to Mold, Moisture, and Your Home - This EPA document emphasizes that the key to mold control is moisture control. It also describes that appliances that produce moisture [and by extension, kitchen and bathroom exhausts] should be vented to the outside when possible.
Wisconsin Construction Standards, SPS 321.05(2)(b) indicates that “All exhaust ventilation shall terminate outside the building.”
