Attic Mold and Mildew - Why Is There Mold In My Attic?

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 defects.
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 leaks.
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 well ventilated.
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 stop!

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 an attic access door. Battic Door is the USA distributor of the fireplace draftstopper. To learn more visit www.batticdoor.com
Attic mold is a sure sign of excessive moisture in the home

Frequently asked questions

Have a question about this project?

Comments

Join the conversation

2 of 3 comments
  • I am very glad that I found this blog because so far the tips and methods have been well wrote and interesting getting this side of view on things. In order to get rid of the mold growth and restore the crawl space to its original condition, you will need to clean out the entire crawl space. If you choose to hire a contractor or other professional service provider to dothe cleanup, make sure the contractor has experience cleaning up mold. Thanksfor great service.
  • Shannon Moloney Shannon Moloney on Jun 21, 2016
    If you live in a 4-season area or have high humidity in the summer, you will eventually have mold. I don't care how much you spend to prevent it, it's going to happen. The key is being vigilant in checking, and controlling it. Some of that is replacing stupid diy "fixes" by previous homeowners or shoddy builders. It's a never-ending battle in the South
Next