Attic Mold in the Pacific North West

Attic Mold

Typical mold condition in the attic

Clients will frequently ask where I see molds most frequently. They are almost always surprised when I say attics. However when you look at the winter environment in the Pacific North West, it doesn’t take much to create the environment to grow mold. Attics can have the right temperature, an abundance of moisture and the home structure provides the mold food.  Here are the symptoms:

Dark black staining on wood surfaces — If the wood in your attic shows any black discoloration, the problem has moved beyond moisture; you have mold growing on the surface

Frost on nails

Frost on nails is an indicator of moisture in the attic

Attic feels stuffy — Attics should feel breezy if they are properly ventilated. When an attic is stuffy, that indicates you have a ventilation problem, which often results in mold problems.

Frost buildup on the underside of the roof sheathing in winter — When it’s cold enough outside, water vapor in an attic with improper ventilation can freeze on the underside of your roof. This makes it especially easy to spot.

Wet insulation in the attic — Not only is this a sign that you may (or soon will) have a mold problem, but when insulation gets damp or wet its ability to insulate becomes significantly diminished, costing you extra money to heat/cool your home.

Generally speaking, attic moisture problems that lead to mold growth are most often caused by:

  • Blocked or Insufficient Ventilation
  • Improper Exhausting of Bathroom Fans or Dryer Vents
  • Can  Lights leaking air into the attic
  • Room air leaking into the attic
  • Roof Issues/Leaks
    bathroom vent

    Unconnected vents can add lots of moisture into an attic

So why is it happening?

In the winter during the coldest months as heat up our homes , warm moist air escapes into the cold attic space. This is called the “chimney effect”. When the escaping warm moist air emerges into the cold attic it rises as heat always does. It rises until it hits the cold roof sheathing and condenses. This warm air-mass-meets-cold-surface phenomena results in a condition known as dew point, which creates moisture in the form of water droplets and ice crystals. The nails themselves also will contribute to this moisture problem (see picture) as iron is a good conductor of temperature and will readily convey the biting chill of cold winter air directly inside the attic. Mold spores find their way to the water droplets and settle onto the sheathing. The mold then starts to grow using the wood pulp as a source of food.

White attic mold

White and black attic mold

Most clients will see the mold and be concerned that its black mold. The reality is most household molds are a black mold called aspergillus but there are other type of molds such as white molds, yellow molds (including serpula lacrymans), and blue-green molds (like our good friend penicillium).  In my opinion, its not worth the cost of testing to find out what type it is as there are no good molds that grow in our homes. If you can see it then you should removed it.


Mold mitigation

in the attic should be left to the professionals. You want their expertise to identify the source because it you don’t fix whats causing the issues then you are just covering the symptoms and the cause is still present. If the mitigation company only talks about testing and killing the mold, I would talk to another contractor. Our office can give you names of local contractors who have experience with attic mold and are very good at finding the root cause. Just give us a call at our office for a referal.