Mold in the Attic: What It Means on Your Home Inspection Report

Your inspector saw mold, or dark staining that looks like it, on the attic roof sheathing: the plywood or OSB boards the shingles are nailed to. Reports may hedge ("suspected mold," "possible microbial growth"); under the InterNACHI standards of practice, one of the standards home inspectors work under, inspectors aren't required to determine whether mold is present.

Either way, it points to moisture: the EPA says no mold will grow without water or moisture. So the questions are how far the damage has gone and where the water is coming from.

Why It Matters

The Department of Energy's Building America program explains how attics get wet. In cold weather, warm, moist air leaks from the house into the attic through holes in the ceiling, and its water vapor condenses on the cold sheathing and framing. Its list of causes: cold surfaces, air leakage, high indoor humidity, and too little ventilation or drying; leaky attic ducts make the leakage worse. Building America adds that bath and kitchen fans exhausting into the attic can cause mold and damage the wood (see our page on a bath fan that vents into the attic). A roof leak wets the wood directly.

The damage is why this rates as repair-soon. Building America says elevated moisture from condensation can quickly lead to mold growth, and repeated or long periods of condensation can cause serious structural damage: rot, swelling, and delamination of OSB and plywood, and corrosion and eventual failure of metal fasteners, which can seriously weaken load-bearing parts of the roof. The EPA adds that the longer mold grows, the more damage it can cause.

On health, the EPA's wording is careful: molds have the potential to cause health problems. Inhaling or touching mold or spores may cause allergic reactions in sensitive individuals, molds can cause asthma attacks in people with asthma who are allergic to mold, and mold exposure can irritate the eyes, skin, nose, throat, and lungs. If you have health concerns, the EPA says to consult a health professional before starting cleanup.

Urgent (beyond repair-soon): sheathing that is soft, swollen, delaminating, or sagging; rusted fasteners; dripping wood or soaked insulation; or an active roof leak. Those mean structural damage is underway; get a roofer's evaluation soon.

What to Do Before Closing

• Ask the inspector for details. How large an area, where (near a fan duct, a chimney, or across a whole roof slope), whether the wood was damp or soft, and photos. Inspectors aren't required to enter an attic that isn't readily accessible, so ask whether they went in.
• Size it up the EPA's way. The EPA says that if the moldy area is less than about 10 square feet (less than roughly a 3 ft. by 3 ft. patch), in most cases, you can handle the job yourself. If there has been a lot of water damage, and/or mold growth covers more than 10 square feet, it says to consult its guide Mold Remediation in Schools and Commercial Buildings, which applies to other building types too.
• Get the right pros to look. A roofer for leaks, vents, and the sheathing; for cleanup, the EPA says to choose a contractor with experience cleaning up mold.
• Talk to your agent. Your real estate agent can advise whether to ask the seller to repair it or offer a credit within your inspection contingency.

For other items on your report, see more findings in our inspection report decoder.

What to Do After You Move In

Fix the moisture first. The EPA says that if you clean up the mold but don't fix the water problem, the mold will most likely come back. Building America's fixes for a vented attic: seal air leaks from the house, keep intake vents low (usually the soffits) and exhaust vents high (usually the ridge) with baffles keeping the soffit vents clear, vent every exhaust fan outdoors, and keep indoor humidity down; the EPA suggests below 60 percent, ideally 30 to 50 (our page on window condensation shows how to measure it). A roof leak needs a roofer.

Then clean up. The EPA says to scrub mold off hard surfaces with detergent and water and dry them completely. It doesn't recommend bleach or other biocides as a routine practice, and it notes that dead mold may still cause allergic reactions in some people, so it must be removed. Don't paint or caulk over mold.

Hold off on new insulation. Building America's assessment guide for attic energy upgrades says to fix fans venting into the attic and roof leaks first, and to have a mold remediation professional inspect and remediate any mold before work proceeds.

Can You Fix It Yourself?

Small patches, maybe. If the moldy area is less than about 10 square feet, the EPA says in most cases you can handle the job yourself; it suggests an N-95 respirator, long gloves, and goggles without vent holes. Step only on the framing, and stop if the insulation is loose and pebble-like: it may be vermiculite, which should be left undisturbed.

Larger growth, damaged sheathing, and new roof vents are jobs for a mold remediation contractor and a roofer; wiring and light fixtures belong to a licensed electrician. Our guide to DIY versus hiring a pro can help with the rest.

Frequently Asked Questions

Should I have the attic tested for mold?

Usually not. The EPA says that in most cases, if visible mold growth is present, sampling is unnecessary, and no EPA or other federal limits have been set for mold. If you do test, it says to use professionals experienced in mold sampling.

Is mold in the attic a deal breaker?

It depends on the cause and extent. A fixable fan duct or leak with sound wood is a contained repair; widespread growth, damaged sheathing, or an unexplained moisture source is a bigger job. Get it evaluated before your contingency ends.

Will the stains go away after cleanup?

Not always. The EPA says mold may cause staining and cosmetic damage that can't always be cleaned away. What matters is that the moisture source is fixed, the growth is removed, and the wood is dry and sound.

The Bottom Line

Mold on attic sheathing means moisture is reaching the roof wood. Ask the inspector how much there is and whether the wood is damaged, have a roofer and a mold contractor look before your contingency ends, and use the EPA's 10-square-foot line to judge who cleans it up. Fix the moisture source first, or the mold will most likely return.

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