Mold on wood in the basement: joists, framing and stored items

Do this first: check the wood and the moisture

1. Put on protection before you get close. EPA says you may want to wear an N-95 respirator, and it recommends long gloves and goggles without vent holes. ^[1]
2. Measure the area. EPA says that if the moldy area is less than about 10 square feet, roughly 3 feet by 3 feet, in most cases you can handle the job yourself. ^[1] On joists, add up every bay that has growth.
3. Press the wood with a screwdriver tip. The Forest Products Laboratory says brown-rotted wood can crack across the grain, shrink, collapse and crush into powder, and white-rotted wood often feels spongy. ^[2] Sound wood resists.
4. Check the humidity. EPA says a humidity meter is a small, inexpensive ($10 to $50) instrument sold at many hardware stores, and that indoor humidity should stay below 60 percent. ^[1]
5. If you have a pin moisture meter, test the wood. The Forest Products Laboratory says fully air-dried wood usually reads no more than 20 percent and that this gives a reasonable margin of safety against fungal damage. ^[2] NC State Extension adds that mildew will continue to grow as long as wood has a moisture content above 20 percent. ^[3]
6. Look for the water: drips from pipes or the laundry above, wet stored boxes, a ring of dampness at the base of the walls, or an open sump pit. UMN Extension lists the damp ring and open sump pits among the ways moisture gets into basements. ^[4]
7. Photograph everything with the date.

Why basement wood gets moldy

Mold on wood needs only damp surfaces, not standing water. The Forest Products Laboratory says the water vapor in humid air will not wet wood enough to support significant decay, but it will permit development of some mold fungi. ^[2] University of Missouri Extension says the molds that cause mildew flourish where it is damp, warm, poorly lit or poorly ventilated, including cellars, and develop most often on materials such as wood and paper. ^[5]

• Summer condensation. University of Minnesota Extension says warm, humid outside air condenses on cool basement walls and floors, and homeowners often mistake that moisture for a leak. ^[4]
• Moisture through the concrete. UMN says water drawn up through the footing and slab creates the ring of dampness seen at the base of many basement walls. ^[4] Sill plates and bottom plates often sit right there.
• Rain and drainage. UMN says failing to slope the ground away from the foundation, or lacking a good gutter and downspout system, is common. ^[4]
• Open sump pits. UMN says the house draws moist air in through foundation openings, including open sump pits, which should have an airtight cover. ^[4]
• Plumbing and appliance leaks dripping onto joists and subfloor from the floor above.
• A past flood. A federal guide from CDC, EPA, FEMA, HUD and NIH says that if your home flooded and you could not dry it within 24 to 48 hours, you should assume you have mold growth. ^[6]

The musty smell often comes first. The mold smell in basement page covers tracking that down.

Surface mold, stain or rot? How to read the wood

This table is about the condition of the wood, not the type of mold. Do not try to name a mold by its color: EPA says molds come in many colors, including white and black, and CDC says all molds are treated the same for removal. ^{[1] [7]}

Table sources: Forest Products Laboratory (FPL) Wood Handbook ^[2] and K-State Research and Extension, which says white growth on anything other than concrete or masonry is most likely mold. ^[8] The white mold in crawl space page explains the water and vinegar test.

Mold is a warning even when the wood is firm. The Forest Products Laboratory says stain and mold fungi affect wood strength only slightly, but make wood more absorbent and more wettable, which can lead to decay fungi, and that early decay may be hidden in discolored areas. ^[2] EPA says that with long-term leaks molds can weaken floors and walls as they feed on wet wood, and that if you suspect mold has damaged building integrity, you should consult a structural engineer or another professional with expertise in this area. ^[9]

How to clean mold off joists, studs and subfloor

EPA's remediation table, written for clean-water damage, lists wood surfaces under 10 square feet as a job for a minimum N-95 respirator, gloves and goggles, with no containment required, using wet vacuuming, damp wiping or HEPA vacuuming. ^[10] Its damp wipe method removes mold by wiping or scrubbing with water, or water and detergent, then drying quickly and thoroughly. ^[9]

1. Fix the leak or start lowering the humidity first. EPA says that if you clean up mold but do not fix the water problem, the mold will most likely come back. ^[1]
2. Move stored items out of the area and cover what stays with plastic.
3. Put on protection: EPA says you may want to wear an N-95 respirator, and it recommends long gloves and goggles without vent holes. ^[1] CDC says people with allergies, asthma, COPD, lung disease or weakened immune systems should not take part in cleanup. ^[11]
4. Scrub the wood with a stiff brush, detergent and water. Use as little water as you can so you do not soak it.
5. Wipe with a clean damp cloth and let the wood dry fully, with a fan and dehumidifier running.
6. Once the wood is dry, HEPA vacuum the area. EPA recommends HEPA vacuums for final cleanup after materials are thoroughly dried. ^[9]
7. Check again in a week. New growth means the moisture is still there.

Some staining may stay. EPA says mold may cause staining and cosmetic damage, and it may not be possible to restore an item's original appearance. ^[12] Do not paint or seal over mold; EPA says to clean and dry surfaces first, because paint over moldy surfaces is likely to peel. ^[1] On bleach, EPA says a biocide such as chlorine bleach is not recommended as a routine practice during mold cleanup, and never mix bleach with ammonia. ^[13]

Boxes, books and furniture stored in the basement

Stored things often hold mold longer than the framing does. A federal guide from EPA, CDC, FEMA, HUD and NIH says you may see or smell mold on clothing, furniture, cardboard boxes or books. ^[6] EPA says absorbent or porous materials may have to be thrown away if they become moldy, because mold can fill their crevices and be difficult or impossible to remove completely. ^[1]

• Cardboard boxes: usually toss the box and repack what was inside after cleaning it.
• Books and papers: EPA's table lists HEPA vacuuming for moldy books and papers. ^[10] For items that matter, EPA says you may wish to consult a specialist and check references. ^[1]
• Solid wood furniture: NC State Extension says it can usually be restored unless it was in water for several days to a week and the damage is severe. ^[3]
• Particleboard or veneer furniture: NC State Extension says that if the particleboard underneath has swollen, the damage will be permanent. ^[3]
• Fabric, rugs and upholstery: Missouri Extension says mildew discolors fabrics and can eat into them until they rot. ^[5] Launder what you can and discard moldy upholstery you cannot dry.

Going forward, store things off the floor and away from outside walls, in closed plastic bins rather than cardboard.

Dry the wood and keep it dry

Table sources: EPA, ^[1] ENERGY STAR, ^[14] Forest Products Laboratory ^[2] and EPA's flood cleanup page. ^[15]

• Run a dehumidifier with basement doors and windows closed, and drain it by hose if you can. ^[14]
• Do not ventilate with humid summer air. UMN Extension advises against ventilating the basement directly with warm, humid air when condensation is the problem. ^[4]
• Fix the outside. UMN says to slope soil away from the foundation at least 1 inch per foot for 6 feet and to extend downspouts at least 4 feet beyond the wall. ^[4]
• Cover the sump with an airtight, childproof lid. ^[4]
• Do not enclose damp framing. UMN Extension says walls must be dry before insulating. ^[4]

A dehumidifier treats the air, not a leak. UMN Extension says dehumidification can reduce the symptoms of humidity and odor but is not a permanent or complete solution, and that in a basement with moisture problems, drying the air can draw moisture in more rapidly. ^[4] Fix the grading, gutters and leaks too.

When to call a mold remediation company

• More than about 10 square feet of mold. EPA points larger jobs to its remediation guide for schools and commercial buildings, which it says applies to other buildings too. ^[1]
• Wood that is soft, crumbly or sagging. EPA says to consult a structural engineer or other professional if you suspect mold has damaged building integrity. ^[9]
• Mold behind finished walls, ceilings or under flooring. EPA says to consider hiring an experienced professional if you believe you have hidden mold. ^[1]
• The basement flooded or had a sewer backup. EPA says to call in a professional with experience cleaning buildings damaged by contaminated water. ^[1]
• The wood will not dry, or growth returns after you fixed the humidity.

For budgeting, HomeAdvisor's June 2026 cost guide lists basement mold remediation at $500 to $3,000. ^[16] Insurance often depends on the cause: Washington's insurance commissioner says homeowner insurance usually does not cover gradual leaks, such as a leaking foundation, or mold unless it comes from water damage your insurance covers. ^[17] Check your own policy.

Common questions