Here is a related article I wrote - hope it helps.
Got Attic Mold? Lets Talk Energy Conservation! - by Mark D. Tyrol,
www.batticdoor.com - December 2004
It happens to countless homeowners around the end of the year - you
make the annual visit to your attic to collect the holiday decorations
and what do you find? Spots and blotches covering the bottom of the
roof sheathing. Worse yet - it turns out to be attic mold!
What does energy conservation have to do with mold in the attic? Well
if you take a step back and consider how the house behaves as system,
they are often directly related.
Building science experts have long been using the "house as a
system" approach to diagnose the cause and origin of building
For example, ice dams. These are often caused by warm air seeping into
the attic which causes the snow and ice on the roof to melt. The water
drains to the edge of the roof (which is colder than the rest of the
roof because it is an overhang and not warmed by the attic), freezes
and creates an ice dam. As this process is repeated daily, the ice dam
grows larger. Eventually water is forced under a shingle where it can
seep into the house.
Understanding how the house behaves as a system and the various causes
and effects is necessary to diagnose most building related problems.
But how about that attic mold? How did it get there?
Mold requires chronic moisture to form and to thrive, so source(s) of
moisture must be present. Possibly the moisture came from outdoors. The
roof is newer and a quick check of the roof shows no obvious damage or
Possibly the moisture came from indoors. During the heating season, the
interior of the house frequently has high moisture levels, especially
bathrooms and kitchens. A quick check shows that all bathroom fans,
kitchen vents, etc. are properly ducted completely outdoors and not
into the attic. The amount of insulation looks good and the attic is
Don't give up - you are almost there! Remember the house as a
system? You know that warm, moist air is in the house, but how is it
getting into the attic?
By air leaks! Air leaks are the leading source of energy loss in most
houses, and a frequent source of chronic moisture that can cause attic
mold. Most homeowners are well aware of air leaks around windows and
doors (especially old ones), but many overlook the numerous gaps
leading directly into the attic!
Have a look around the attic and you may find large gaps around
recessed lights and fans, holes where wires or pipes are installed,
even large gaps around the chimney. And don't overlook the whole
house fan and especially the folding attic stair - a big, uninsulated
hole in your ceiling that is often overlooked!
These gaps can add up to a large hole that allows warm, moist air from
the house to flow right into the cold attic. The warm moist air
condenses on the cold roof sheathing, creating chronically damp
conditions that can lead to attic mold growth. And the energy loss -
it can be like leaving a window open all winter long!
Seal these air leaks and you stop a significant moisture source. And
just think of all the energy you can save and the cold drafts you can
Mark D. Tyrol is a Professional Engineer specializing in cause and
origin of construction defects. He developed several residential energy
conservation products including an attic stair cover and a fireplace
draftstopper. To learn more visit www.batticdoor.com