There was a period of time when the attic was considered “outdoors,” and in a sense that was true, in that the attic space does not “communicate” in any way with the house interior (if only this were actually true). Unfortunately that is in an “ideal” world.
There are many ways the house/attic barrier is compromised: missing access hatch weather-stripping, missing fire-stopping/draft-stopping, can lights, crappy insulation that does not provide an adequate air barrier around junction boxes, and exhaust vents that terminate in the attic, are some of the main ones.During that period of lack of awareness, many builders would terminate exhaust fans in the attic because they thought of this space as “outdoors.” The reality is that it is only “partially” outdoors–a sort of “ventilation purgatory” where things may or may not be OK depending on how the offending component behaves–kind of like the more infamous purgatory I am told.
Another thing that makes the attic NOT outdoors is that its own little micro-climate is created when it is heated by the sun hitting the roof, when cold snow piles up on the roof, and when winds blow by the roof creating a negative pressure on the attic. As a Seattle Home Inspector, I routinely recommend that exhaust fans be properly vented to the true exterior of the building–instead of into the attic. These vents carry moisture laden air into a potentially cold place where the moisture can condense on cold surfaces. This is often responsible for staining of sheathing, rusting of metal components and it can result in decay/rot and mold growth on the wood roof structures.
Dryers vented into attics can actually do considerable damage to the roof structure–besides creating a fire hazard with all the lint.Many builders would attempt to “improve” this approach by merely aiming the vent pipe at one of the screened attic roof vents–not realizing that over time these screens would plug with lint and result in the roof vent becoming non-functional for the job it was put there to do (vent the attic) and also create a baffle to redirect the exhausted air back into the attic. The following pictures are excellent examples of just how bad this condition can get.
Can you see the staining and rusting around the roofing nails that stick through the sheathing? In this case, all of the home’s exhaust fans terminated in the attic and contributed to more moisture than the roof venting system could adequately vent away. The one pictured is a normal everyday bathroom exhaust fan–not a dryer vent–as the amount of lint might make one think.
All exhaust fans from the interior of the home should be ducted directly to the exterior of the home to a cap with a proper back-draft damper. Current regulations also require insulation on the duct work.
By Charles Buell, Real Estate Inspections in Seattle
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