Attics are easy to ignore, which is why mold there often goes unnoticed until it is widespread. It usually shows up as dark staining on the underside of the roof sheathing, sometimes with damp insulation or a musty smell that drifts into the rooms below. The cause is almost always moisture the attic cannot get rid of.
This guide covers what attic mold looks like, what causes it, how it is removed, and what it costs.
What attic mold looks like
- Dark spotting or staining on the underside of the roof sheathing, often in patches between rafters
- White or gray fuzzy growth on sheathing, rafters, or trusses
- Damp, matted, or stained insulation
- Rusty nail tips poking through the sheathing, a sign of repeated condensation
- Water stains on rafters, sheathing, or the ceiling below
- A musty smell in the attic or upstairs rooms
Mold comes in many colors, and white attic mold is still mold. If the attic has been damp enough for growth, the response is the same regardless of color.
Common causes
- Roof leaks. Damaged shingles, flashing around chimneys and vents, and storm damage let water in.
- Fans venting into the attic. Bathroom, kitchen, and dryer vents that end in the attic instead of outside pump moist air straight onto the sheathing.
- Poor ventilation. Soffit vents blocked by insulation, too few vents, or vents that do not let air flow through.
- Air leaks from the house. Warm, humid air rises through gaps around light fixtures, the attic hatch, and plumbing penetrations. In colder climates, it condenses on cold sheathing in winter.
- Air conditioning in the attic. Ducts and air handlers in hot attics can sweat, and drain pans or condensate lines can overflow. The EPA stresses that controlling moisture around cooling equipment, such as making sure drain pans slope toward the drain, is the most effective way to prevent growth.
Why it matters
- The structure. Sheathing and framing that stay wet for long periods can weaken and rot.
- The rest of the house. Air and spores can move from the attic into the living space through gaps in the ceiling and through ducts that run in the attic.
- Insurance and resale. Attic mold often comes up in home inspections, and long-term moisture problems are usually excluded from coverage.
How attic mold is removed
- Fix the cause first. Repair the roof, reroute fans to vent outside, clear or add ventilation, seal air leaks, and fix any air conditioning drainage or duct condensation. Without this step, the mold returns.
- Protect the house and any equipment. Air conditioning components in the attic are sealed off so spores are not pulled into the system.
- Remove wet or moldy insulation. It is bagged and removed, and replaced later.
- Clean the wood. Sheathing and framing are HEPA-vacuumed and cleaned. Some companies use wire brushing or sanding, and others use media blasting, such as dry ice or baking soda blasting, to clean large areas of sheathing.
- Coat only after cleaning. Some contractors apply a mold-resistant coating to cleaned wood. A coating is not a substitute for removing the growth.
- Dry and verify. Moisture readings, and sometimes clearance samples, confirm the attic is clean and dry before new insulation goes in.
Can you do it yourself?
The EPA says homeowners can often clean mold areas smaller than about 10 square feet, but attics are a hard place to work: temperatures can be extreme, footing is limited to joists, insulation fibers irritate skin and lungs, and a misstep can go through the ceiling. Most attic mold also covers more than 10 square feet by the time it is found. For anything beyond a few spots, a professional is the safer choice. See DIY vs. professional mold removal.
What it costs
HomeGuide puts mold removal in part of an attic at about $1,500 to $6,000, and $6,000 to $15,000 for a whole attic, particularly when access is limited or the insulation must be replaced. Insulation replacement runs about $1 to $4.50 per square foot, and repairing a small roof leak about $150 to $1,000, according to the same data. See our mold remediation cost guide.
Insurance
If the mold followed a sudden, covered event, such as wind damage to the roof during a storm, homeowners insurance may pay for it up to the policy's mold limit. Mold from a slow roof leak, fans venting into the attic, or long-term ventilation problems is usually treated as maintenance and excluded. See does homeowners insurance cover mold.
Attic mold in Florida homes
Florida attics get extremely hot, and many hold the air handler and ductwork. Sweating ducts, overflowing drain pans, and roof damage after storms are the usual causes of attic mold there. A musty smell upstairs after a hurricane or a long trip is a reason to take a look. See local pages for Sarasota, West Palm Beach, and the rest of Florida.
Next step
If you own your home and see staining on the roof sheathing, damp insulation, or smell mold coming from the attic, call the number on this page to be connected with an independent local mold inspection or mold remediation company.