Why Does Mold Grow in Attics and Crawl Spaces?

This new post is in response to a question raised by another post of mine. 

"Mold - Where and How Does It Grow?" 

Bob asked, 

"Can I ask why there is often mold in attics and crawl spaces ? It makes no sense, because mold and mildew need humidity. Because I have even heard that in many cases, you can have mold in your attic without it having any leak from the roof. Any opinions on this ???"



Bob, here is the answer.

Great question. There are many reasons that mold can grow in attic and crawl spaces. All that is needed is moisture, a food source, and the omnipresent mold spores can grow. 

Any broken or leaky pipe running through these areas will suffice, but there are other more subtle moisture sources. These are some I have actually seen.

Possible moisture sources in an attic:

1. A leak from blown-off shingles or damage to the roof.
2. A leak around a protrusion, like a chimney, furnace flue, or parapet wall rising up through the roof.
3. A clothes dryer or exhaust fan that is vented into the attic.
4. Insufficient ventilation, (lack of soffit, gable, and/or roof vents,) that allows normal moisture to build up in the attic rather than being exhausted outside, especially in climates with normally high humidity.
5. Ice damning will push moisture up under the shingles and into the attic.
6. Water from an air-conditioner or furnace condensate line that isn't drained properly.

Possible moisture sources in a crawlspace or basement.

1. Ground water coming through cracks in the concrete floor or walls in a basement.
2. Ground water percolating up through the dirt in the crawl space.
3. Water from a leaky toilet or drain line on the main floor that drops into the crawl space.
4. A clothes dryer or exhaust fan that is vented into the crawl space.
5. Insufficient ventilation that allows normal moisture to build up rather than being exhausted outside, especially in climates with normally high humidity.
6. Water from an air-conditioner or furnace condensate line that isn't drained properly.
7. Broken or disconnected drain lines in the crawl space.

All of these, and possibly other sources, can provide the moisture needed for mold to grow. Because we seldom go into the attic or crawl space, we are not able to monitor these areas and these conditions can cause significant damages over time, including rot and mold.

Regular inspections, or just being aware when you are in these locations, will help to identify and correct these issues before they become problems. - dlm