Grow mold in your attic (vent to the soffit)

Home Inspector with Perfection Inspection, Inc.

Ah mold.  It is such a hot button.  I know just by putting the word MOLD into my title this post will get Moldy sheathingattention.

People are interested, but I am still surprised at the lack of knowledge or the inaccuracy of knowledge (even you agents, who need to know the basics).

This is not intended to be a general knowledge post. (go here for that)  This is a heads up for everyone on the issues concerning a currently accepted means of exhausting bathroom vents.  Currently it is acceptable to duct bathroom vents to an attic vent.  This is usually a good thing and definitely better than venting directly into the attic. 

Recently I came across a very new home (only four years old) that had some mold growth in the attic.  Not really a huge amount, however mold spores are microscopic and you cannot determine if it is affecting Indoor Air Quality without getting a lab involved.  With closer investigation it could be noted the exhaust fan for the shower and toilet area was ducted to the nearby soffit vent.   This is currently acceptable however in this case it was the root of the issue.

The way an attic vent system works is like a chimney, as the roof heats cool air is pulled into the soffit vents and hot air is exhausted out the ridge vents.  So as the diligent home owners ran their exhaust fans during the steamy shower all of the warm steam was pointed at an intake vent!!  All the moisture exhausted toward the vent and promptly turned around and was able to condense on the cool attic surfaces as the soffit vent did its job.Visual picture of thermal issueThermal image of moisture in attic

Comments (2)

Fred Chamberlin
Guild Mortgage Co - Oak Harbor WA - Oak Harbor, WA
Oak Harbor/Whidbeynulls, #1 Experienced FHA Mortgage Consultant

Always such great content Jim. Thanks,

Dec 20, 2008 08:47 AM
Jhake Turner
Molds are part of the natural environment. In outdoors, molds play an important part in nature by breaking down dead organic matter such as fallen leaves and dead trees, etc. But indoors, mold growth should be avoided and prevented. Molds reproduce by means of tiny spores; the spores are invisible to the naked eye (only on microscope) and float through outdoor and indoor air and contaminate areas. Mold may begin to grow indoors when mold spores land on surfaces that are wet or areas with moisture. There are many types of mold, and none of them will grow without water or moisture. So, moisture plays a great part of it. They attack usually on foods but they also attack non-food items like leather, wood and porcelain. Do you notice your allergic reactions are worse when you're at home but you feel better when you go out? Well, expect it. If so then it's especially likely you could have mold. Don’t go weary of staying in one place. Find a way for mold detection
Mar 24, 2014 09:10 PM