Wednesday, April 30, 2014

Where do your bathroom (or kitchen, or dryer) vent fans exhaust to?

One of the frequent things I find on home inspections is incorrectly vented exhaust fans.  First, let's look at the purpose of these fans.  They are designed to remove the moisture that is created from showering, cooking, or drying clothes.  Anyone who has had me do an inspection knows how much I harp on moisture control.  Moisture is one of the things that can rapidly cause damage to a house, be it from material deterioration, mold, or even creating an environment conducive to termites and other wood destroying insects.  Vent fans are supposed to vent to the exterior of the house.  This can be either through a roof vent, a wall vent, or a soffit vent.  Many times though, I find the fans are simply exhausted to the attic.  Sometimes, I find them exhausted to the soffit space, but not actually outside through the soffit.  A good attempt, but still not a correct attempt.  When the hot moist air from your bathroom or kitchen is exhausted into the attic, most of the moisture ends up condensing on the surfaces in the attic, especially during the winter.  This can rapidly cause severe damage to the structure of the attic, as well as lead to mold and other problems.  I have frequently found attics with areas of mold growth and delamintaed plywood.  Sometimes, it's a problem with the roof ventilation as a whole (a topic for another day), but most of the time the cause can be traced to a vent fan exhausting to the attic.

What to do?  First, take a look in your attic.  Especially if it's been a long time since you've been up there.  Look above your bathrooms to see if there is a tube leading outside.  If it goes to the roof, check outside to make sure there is a vent in that same location.  If it goes to the soffit, make sure there is a vent through the soffit in that area.  If your bathrooms are on a lower level, they may vent through the wall.  In that case, turn on the vent fan, or your dryer, and look to see if air is exhausting.  Most of the time, you can see the flapper moving or fully open.  If it's not, you may have a problem, and I would recommend getting a licensed contractor in to help you out.  And while you're at it, make sure the dryer vent line is cleaned on a regular basis.  Lint builds up and is very flammable!

Bathroom vent to attic causing delamination of the roof plywood and mold.
A soffit vent.  Even though the soffit is vented (the perforations)
you still need to exhaust a vent fan through the soffit.
This is an easy to fix problem that can save you a lot of trouble in the long run.


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