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Mold   Mold

High indoor humidity levels often cause condensation on cold surfaces such as windows. If moist air is allowed to get into the attic, more serious problems may arise, such as mold, mildew and rotting wood beams. Failed roofs and the potential for risks to family health such as respiratory difficulties and aggravated allergies can follow.

If mold already exists, it will need to be completely cleared up before taking action to prevent it happening again. Prevention is quite straightforward: isolate the attic from the living space with proper air sealing and insulation and reduce the sources of excess humidity.


There are several sources, both exterior and interior. If the roof is old and leaking, obviously that is an exterior source. But lets talk about interior sources that are often overlooked, but are not too difficult to correct.

Interior sources include air leaks from the house into the attic. Moisture is carried by air movement from the warm home into the cold attic, where the moisture in the air condenses and wets cold surfaces, such as the roof sheathing and rafters. Over time, chronic moisture causes mold and mildew.


The largest "holes" leading directly from the house to the attic are the attic access and the whole house fan.

When an attic access is a fold-down stairway, it was difficult to control moisture and heat loss. The Battic Door Attic Stair Cover is a low-cost, easy-to-install solution to this common problem.

When a whole house fan is installed in the home, it was difficult to control moisture and heat loss. The Battic Door Whole House Fan Cover and Battic Door Whole House Fan Shutter Seal provide two low-cost, easy-to-install solutions to this common problem.

Here are several documents written by Zerodraft (an expert and manufacturer of sealants and foams) that describe other sources of air leaks.

Adobe PDF Seal party walls (544 kb)
Adobe PDF Seal recessed light fixtures (138 kb)
Adobe PDF Seal the attic hatch (306 kb)
Adobe PDF Seal the baseboards (127 kb)
Adobe PDF Seal electrical outlets (111 kb)
Adobe PDF Seal the attic (167 kb)
Get Adobe Acrobat Reader

Here is a recent article written by Mark Tyrol, Owner of Battic Door, and published Nationwide!

Got Attic Mold? Lets Talk Energy Conservation!
By Mark D. Tyrol, P.E., Battic Door Energy Conservation Products

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 a fireplace draftstopper. To learn more visit