Mold in the Home:
What the EPA Says About Cleanup

What Mold Is and What It Needs

Molds are fungi that grow as multicellular filaments called hyphae. Outdoors they break down dead organic material. Indoors they damage building materials and can affect the people living there.

Mold reproduces through airborne spores. Spores are present almost everywhere outdoors and enter homes through windows, doors, HVAC systems, clothing, and pets. They cannot be eliminated from a house. They only become a problem when they land on something damp.

Three things let mold grow:

• Moisture. The most controllable factor. Without it, mold cannot grow even when spores are present.
• Temperature. Mold grows in roughly the 40 to 100 degrees F range, which overlaps the range people find comfortable.
• Organic material. Drywall, wood, ceiling tiles, carpet, dust, and even paint can serve as food.

The EPA says that if wet or damp materials are dried within 24 to 48 hours after a leak or spill, mold will not grow in most cases. That window is why fast response to leaks matters.

Where the Moisture Comes From

• Outdoor sources: rain, flooding, groundwater, high outdoor humidity, and water entering through the foundation or roof.
• Indoor sources: cooking, bathing, laundry, humidifiers, HVAC condensation, leaking pipes and appliances, and wet basements.
• Construction defects: missing or misplaced vapor barriers, insufficient ventilation, and thermal bridges that cause condensation.

Health Effects of Mold Exposure

Mold can produce allergens and irritants. Common reactions include coughing, wheezing, a stuffy or runny nose, sinus congestion, red or watering eyes, throat irritation, and skin irritation. People with asthma or allergies may see their symptoms worsen.

Those most at risk include infants and young children, older adults, people with asthma or allergies, people with chronic lung disease, and people with weakened immune systems. In immunocompromised people, some molds can cause serious lung infections. People without sensitivities may notice no symptoms even when mold is present.

Common Indoor Molds

Identifying the species is not necessary for cleanup. The approach is the same regardless of type. For reference, these are commonly named indoors:

• Cladosporium: olive-green to brown or black colonies on fabrics, wood, and ducts.
• Penicillium: blue or green and powdery, often on water-damaged wallpaper, insulation, and carpet, with a musty odor.
• Aspergillus: many colors, found in dust, building materials, and HVAC systems.
• Stachybotrys (often called “black mold”): a slimy, dark growth on cellulose-rich materials that stay wet for extended periods. Color alone does not identify a species.
• Alternaria: velvety dark green or brown growth in showers and under sinks, and a common allergen.

Finding Mold and Hidden Moisture

Visible growth can be fuzzy, powdery, or slimy in white, green, gray, black, or other colors. Other signs include a persistent musty or earthy odor, yellow or brown stains on walls and ceilings, and paint or wallpaper that peels or bubbles. Stains and bubbling suggest moisture migrating through the material, and mold may be behind the surface.

Household bleach is sometimes used to tell mold from dirt. That test is not part of EPA guidance and is not recommended here. When in doubt, treat a suspect area as mold and look for the water source.

For more on these areas in local homes, see the guides to crawl space mold in Portland homes and attic mold in Portland homes.

When to Call a Professional

The EPA’s guidance on home mold sets the dividing line at about 10 square feet. A licensed remediation contractor performs remediation work beyond what a homeowner can safely handle.

The EPA recommends consulting a professional when:

• Mold or water damage covers more than about 10 square feet (roughly 3 ft by 3 ft).
• Mold is in the HVAC system or air ducts.
• The water source was sewage or other contaminated water.
• Occupants have health symptoms during or after exposure, or have health concerns.
• Structural materials such as joists or studs are affected.
• Mold returns after cleanup, which usually signals an unresolved moisture source.

Cleanup by the occupant is generally within EPA guidance when:

• The affected area is under about 10 square feet.
• The moisture source has been found and corrected.
• The mold is on hard, non-porous surfaces such as tile, glass, or metal.
• No hidden mold is suspected behind walls.
• The person doing the work does not have asthma, allergies, or immune concerns.

For buyers weighing whether mold testing is warranted, see when a mold inspection makes sense in Portland. Note that the EPA says sampling is usually unnecessary when mold is visible.

The 24 to 48 Hour Water Damage Response

The EPA’s water damage guidance lists what to do with common materials after a leak or flood. The table below summarizes it.

How Cleanup Is Scoped by Size

EPA Table 2 in “Mold Remediation in Schools and Commercial Buildings” scopes work by the size of the affected area. It uses three sizes.

• Under 10 sq ft. Minimum protection is an N-95 respirator, gloves, and eye protection. No containment is required.
• 10 to 100 sq ft. An N-95 or a limited air-purifying respirator with a HEPA filter. Limited containment is generally recommended, using single-layer 6-mil polyethylene sheeting.
• Over 100 sq ft. Full-face powered air-purifying respirator (PAPR) with a HEPA filter. Full containment is recommended, with double-layer polyethylene and an airlock or decontamination chamber.

Some older guides split this into four “levels” based on New York City Department of Health guidelines. The EPA uses the three sizes above. Anything beyond the smallest tier is generally a job for a licensed remediation contractor.

The Cleanup Process Step by Step

These are the steps outlined in EPA guidance. Larger or contaminated jobs belong to a licensed remediation contractor.

1. Fix the moisture source. Repair leaks, remove standing water, and reduce humidity. Do not clean mold until the moisture problem is resolved.
2. Protect yourself. Use the protection that matches the size of the area (see the PPE section below). Always wear gloves and eye protection.
3. Set up containment. Close doors and cover openings with polyethylene sheeting. Larger jobs call for negative air pressure.
4. Remove porous materials. Moldy drywall, carpet, ceiling tiles, and insulation are typically bagged and discarded. Double-bagging in heavy polyethylene limits spore release.
5. Clean hard surfaces. Scrub with detergent and water. The EPA does not recommend bleach or other biocides as routine practice, because dead mold can still cause reactions and has to be physically removed.
6. Dry thoroughly. Fans and dehumidifiers dry the area. Surfaces should be completely dry before reconstruction.
7. Verify, then rebuild. Look for no visible mold, no musty odor, and no remaining moisture before replacing materials.

Cleaning Different Surfaces

• Hard, non-porous (tile, glass, metal): scrub with detergent and water, rinse, and dry completely.
• Semi-porous (wood framing, concrete): may be cleaned with a wire brush or sanding, a detergent scrub, and a HEPA vacuum. Badly damaged wood may need replacement.
• Porous (drywall, carpet, ceiling tiles): generally cannot be cleaned adequately. Remove and discard.
• Books and documents: air-dry or freeze early to halt growth, and discard if heavily contaminated.
• Clothing and fabric: launder with detergent in hot water if the fabric allows. Discard heavily affected items.

If a material cannot be dried, the EPA’s guidance leans toward discarding it. Painting over mold is not a fix, and the moisture source always comes first.

Bathrooms and Kitchens

Bathroom prevention: run the exhaust fan during and for about 30 minutes after showers, repair leaky faucets and toilet seals promptly, recaulk when caulk cracks, and hang wet towels and mats to dry. Cleaning: scrub grout with a stiff brush and detergent, replace caulk that is stained through, and check under and behind the toilet.

Kitchen prevention: use the range hood and vent it outside, check under the sink for plumbing leaks regularly, clean the refrigerator drip pan periodically, and dry the dish rack. Cleaning: wipe cabinet interiors under the sink, clean backsplash grout, and inspect the dishwasher seal.

Basements and Crawl Spaces

Basements are higher risk because below-grade walls contact soil moisture, cool surfaces collect condensation, airflow is limited, and flooding and sewer backups are more common. In Portland, crawl spaces add pooled water, high humidity, and vented-versus-sealed design questions. See crawl space mold in Portland homes for local detail.

Crawl space best practices commonly cited include a polyethylene vapor retarder over bare soil and annual checks for standing water and condensation. Ventilation requirements and sealed crawl space approaches vary by building code and conditions, so local code and a qualified contractor govern the specifics.

Typical sequence for existing basement mold: find and fix water entry, remove wet or moldy material, HEPA vacuum dry surfaces, scrub with detergent, dry with a dehumidifier, and then address wall sealing if needed.

HVAC and Ductwork

Do not run the HVAC system if mold is suspected inside it. The system can spread spores throughout the building. HVAC mold is a situation where the EPA recommends consulting a professional.

Central systems circulate air to every room, condensate pans and cooling coils stay moist, and fiberglass duct liner is porous and hard to clean. Signs include a musty smell when the system runs, visible growth on registers or the air handler, allergy symptoms that worsen when the system runs, and dark dust rings around supply registers.

Maintenance that helps includes regular filter changes at the rating the equipment manufacturer specifies, clean drip pans and drain lines, dry ducts, and periodic professional servicing. If ducts are contaminated, a duct cleaning company that is a member of the National Air Duct Cleaners Association (NADCA) is one way to find qualified help.

Methods, Protection, and Containment

The Four Cleanup Methods

• Wet vacuum: for standing water on carpets and hard floors. Use a wet-dry vacuum and clean the tank, hose, and attachments after use. It does not clean porous materials.
• Damp wipe: for hard surfaces with light mold. Wipe with water and detergent, rinse, and dry right away. Dry wiping spreads spores.
• HEPA vacuum: for dry surfaces after cleaning, to pick up settled spores. HEPA filters are rated to capture 99.97% of particles 0.3 microns and larger. Contents go into sealed bags.
• Discard: for porous materials that cannot be adequately cleaned. Double-bag in heavy polyethylene and seal.

Personal Protective Equipment

EPA guidance says always use gloves and eye protection during mold cleanup. Respiratory protection depends on the size and intensity of the work.

• Under 10 sq ft: N-95 respirator, gloves (nitrile or rubber), non-vented goggles, and work clothes that are washed afterward.
• 10 to 100 sq ft: N-95 or a half-face respirator with HEPA (P100) cartridges, long-cuff gloves, disposable coveralls, goggles, and boot covers.
• Over 100 sq ft: full-face powered air-purifying respirator with HEPA filter, a full-body disposable suit, gloves taped to sleeves, and boots or covers. This level of work is for professional contractors.

Disposable respirators and coveralls are not reused. Contaminated protective equipment is bagged and discarded right after use.

Containment Strategies

Containment keeps spores from spreading to clean parts of the home during work.

Limited containment (10 to 100 sq ft):

• Close doors and windows in the affected room.
• Seal supply and return vents with polyethylene sheeting.
• Cover doorways with a single layer of polyethylene taped in place.
• Minimize entries and exits.
• Fold sheeting inward, mold side in, when disposing of it.

Full containment (over 100 sq ft):

• Use double-layer floor-to-ceiling polyethylene barriers.
• Build an airlock entry using overlapping poly curtains.
• Maintain negative air pressure with a HEPA air scrubber exhausting outside.
• Seal HVAC vents, pipe gaps, and penetrations.
• Post warning signs and restrict entry to properly equipped workers.

Moisture Measurement Tools

Several inexpensive tools help track moisture. A moisture meter (pin or pinless) reads moisture content in wood and drywall. A hygrometer shows relative humidity. A humidistat can control a dehumidifier or fan automatically. A thermal imaging camera can reveal temperature patterns that may indicate hidden moisture, but a moisture meter should confirm any suspected wet area.

Keep indoor relative humidity below 60 percent, and ideally between 30 and 50 percent, per the EPA. Thermal imaging is included at no additional charge on every Trusted Home Inspections home inspection, and it is used to document possible moisture patterns, not to diagnose mold.

Top Prevention Tips

1. Fix leaks promptly. Roof, plumbing, and foundation leaks should be repaired quickly so materials dry within 24 to 48 hours.
2. Control humidity. Use dehumidifiers in damp basements and a hygrometer to monitor.
3. Ventilate moisture sources. Bathroom and kitchen exhaust fans should vent outside, not into the attic.
4. Dry wet areas right away.
5. Maintain HVAC systems, including condensate drain pans.
6. Consider mold-resistant products in bathrooms and basements.
7. Check gutters and grading. Soil should slope away from the foundation. Building code commonly calls for about 6 inches of fall within the first 10 feet.
8. Look in damp-prone spots regularly: under sinks, around tubs, and in basements.

Remediation Completion Checklist

This checklist reflects the verification steps in EPA guidance. It is a general reference. A licensed remediation contractor or the project’s written scope governs the actual job.

Mold and Your Home Inspection

A home inspection is a visual, non-invasive review. The inspector documents visible moisture, staining, active leaks, ventilation conditions, and suspected mold, and notes where they were seen. A home inspection does not include mold testing or remediation. Findings are reported with photos and video.

Buying in the Portland area? Read about how a buyer’s home inspection works and what a mold finding in a report means for a homeowner. To book, schedule an inspection with a Certified Master Inspector®.

Primary sources for this guide: A Brief Guide to Mold, Moisture, and Your Home and Mold Remediation in Schools and Commercial Buildings.