Musty Odor in Home: Everything You Need to Know

Written By Adam Paul - Waterproofing Expert

A musty odor, also known as old house smell or basement smell, is a stale, earthy, and damp smell that often signals excess moisture, humidity, or hidden mold growth in a building. Microbial volatile organic compounds (MVOCs) are considered as a musty odor. It is produced by the microbes that grow in enclosed, poorly ventilated, water-damaged, organic areas such as basements, crawl spaces, foundations, attics, bathrooms, closets, laundry rooms, and HVAC systems.

Musty odor occurs due to basement seepage, plumbing leaks, poor ventilation, mold and mildew growth, and damp carpets and upholstery. Musty odor reduces the indoor air quality. Musty odor with mold and mildew may cause respiratory issues in the home. Not only that, musty odor also reduces the property value of the house. Because it indicates a prolonged hidden water problem in the house structure. Musty and moldy odors are two different types. It can be recognized by the sharpness of the smell. 

A proper waterproofing method should be applied to the damaged or problematic area in the home to stop the musty smell permanently. More than that, to prevent the musty odor, you should control the humidity level by installing dehumidifiers, improving ventilation, fixing leaks immediately, and maintaining the HVAC system properly. For the prolonged musty odor, contact us immediately. Aqviz experts are always here to help you.  

What Is the Definition of Musty Odor?

A musty odor is a stale, earthy, and damp smell that often signals excess moisture, humidity, or hidden mold growth in a building. Microbial volatile organic compounds (MVOCs) are considered as the musty odor, and it is produced by the microbes where they grow in enclosed, poorly ventilated, water-damaged, organic areas.

“Musty odor” is commonly described as “old house smell” or “basement smell,” as well. A musty odor also goes by other terms like dank smell, mildew smell, or moldy scent. Living with a musty odor causes several problems. It reduces indoor air quality, triggers allergies and respiratory issues, lowers the property’s value, promotes fungal contamination, and signals hidden structural moisture damage.

Installing a waterproofing membrane and redirecting the water is the only way to eliminate the musty odor in the home. 

What Causes a Musty Odor in the Home?

There are five main causes of musty odor in a home, and each is tied to underlying moisture problems in specific areas of the building.

1. Basement water seepage: Leaks through foundation cracks, floor joints, or hydrostatic pressure lead to stagnant water under the basement slab over time, it causes a strong musty odor in basements.
2. Plumbing leaks: Slow leaks from pipes, faucets, or sump pump failures release moisture behind walls, under floors, or inside cabinetry. Prolonged it results in a lingering musty odor in bathrooms, kitchens, and laundry areas.
3. Poor ventilation: Inadequate airflow traps humidity in attics, crawl spaces, and closets, creating the perfect damp environment for musty odor to thrive.
4. Mold growth on wet surfaces: Mold and mildew develop on wet drywall, wood, or insulation after water intrusion, especially in ceilings, window sills, and behind wallpaper, producing a persistent musty smell.
5. Damp carpets and upholstery: Flooding, spills, or high indoor humidity can soak carpets, rugs, and furniture, leading to trapped moisture and musty odor in living rooms, bedrooms, or basement lounges.

How Musty Odors Affect Indoor Air Quality and Property Value?

Indoor air quality (IAQ) refers to the air condition inside a home, measured by humidity levels, pollutants, allergens, and volatile organic compounds (VOCs). We measure IAQ using digital air quality monitors, humidity meters, and mold test kits from trusted brands like Airthings and Foobot.

A musty odor reduces IAQ by indicating the presence of mold spores, fungal fragments, and high moisture content. These airborne particles worsen asthma, allergies, and respiratory issues, especially in homes with poor ventilation. At Aqviz, we’ve seen musty odor signals deeper issues like subsurface water intrusion or hidden mold colonies, often requiring structural repair.

Musty odor also lowers property value. Homebuyers associate it with neglected maintenance, potential water damage, and costly repairs. Real estate reports from Zillow and NAR confirm that homes with moisture-related smells sell for 10-30% less, depending on severity. A persistent musty odor can derail inspections, delay closings, and force sellers to offer major discounts.

Common Places Where Musty Odor Develops in a Home

Musty odor usually develops in home areas with poor airflow, high humidity, or frequent water exposure. Below are the 7 most musty odor-producing areas in the home.

1. Basement: The Basement is prone to groundwater seepage, foundation cracks, and flooding, especially during rainy seasons. Hence, stagnant moisture and dark conditions encourage fungal growth.
2. Crawl Space: Unsealed crawl spaces absorb ground moisture, which triggers strong musty smells.
3. Attic: The attic is vulnerable to roof leaks, ice damming, and trapped humid air. This causes mold to build a musty odor in the attic, especially in homes lacking proper ridge vents or soffit vents.
4. Bathroom: A Musty odor occurs in the bathroom due to constant exposure to steam,
5. Leaky Plumbing: Leaky plumbing and poor exhaust systems lead to mildew in tile grout, walls, and under sinks.
6. Laundry Room: Laundry room humidity is raised by the overflows, hose leaks, and damp clothes. This causes a musty odor in the laundry room over time.
7. Closet: Closed spaces trap moisture from damp clothes, leaky walls, or adjacent plumbing. This causes hidden mold to grow behind shelves or on drywall.
8. HVAC System: If condensate lines clog or drip pans overflow, moisture inside ducts and air handlers breeds mold. As the system runs, it spreads a musty odor throughout the home.

Difference Between Musty and Moldy Odors

Musty odor is a mild, stale, and earthy smell that typically signals dampness or poor ventilation, often noticed in basements, closets, or crawl spaces. It’s an early warning of moisture buildup, while a moldy odor is sharper, stronger, and more pungent. It usually indicates active mold growth on wet drywall, wood, or insulation.

Can Waterproofing Stop Musty Odors Permanently?

Yes, proper waterproofing can stop a musty odor permanently by removing the moisture sources that allow it to thrive. You can use the waterproofing methods below that our experts always recommend.

In basements, we install interior drainage systems, apply cementitious waterproof coatings, and seal foundation cracks using products like Xypex or Sika.

For crawl spaces, we use vapor barriers, dehumidifiers, and encapsulation systems such as CleanSpace to block soil moisture.

In attics, we prevent roof leaks with roof sealants, improve ventilation, and insulate with closed-cell spray foam to control humidity.

In bathrooms and laundry rooms, we seal tiles with epoxy grout, waterproof subfloors using liquid membranes, and fix any hidden plumbing leaks.

Closets and HVAC systems benefit from fixing adjacent leaks, installing moisture sensors, and cleaning ducts with antimicrobial treatments like BBJ Mold Control.

How to Eliminate Musty Odor in the Home?

Follow these 6 proven steps to eliminate musty odor from your home effectively. At Aqviz, we use this practical approach on real projects using professional-grade tools and materials.

1. Identify the Source: Inspect basements, bathrooms, crawl spaces, and HVAC systems for leaks, moisture stains, or mold patches using a moisture meter like Protimeter Surveymaster or FLIR thermal camera.
2. Dry Out Moist Areas: Use industrial dehumidifiers (like Frigidaire 50-Pint) and high-velocity fans to remove moisture from damp air and surfaces. Open windows for airflow if outdoor humidity is low.
3. Clean Affected Surfaces: Scrub moldy or mildewed surfaces using a mold remover such as Concrobium Mold Control or a homemade solution of white vinegar and baking soda. Use N95 masks, gloves, and scrub brushes.
4. Replace or Deep Clean Soft Materials: Remove wet carpets, upholstery, or insulation if saturated. Steam clean salvageable items with a HEPA-filter vacuum and carpet extractor like Bissell Big Green.
5. Apply Waterproofing Solutions: Seal concrete surfaces with liquid waterproof membranes like DRYLOK, coat crawl spaces with vapor barriers, and use mildew-resistant paint in humid rooms.
6. Ventilate and Monitor Air Quality: Install bathroom exhaust fans, use air purifiers with activated carbon filters, and monitor indoor humidity using a hygrometer (aim for under 50%).

How to Prevent Musty Odor in the Home?

Preventing musty odor starts with controlling moisture and maintaining airflow throughout the home. Aqviz, we recommend these 5 key methods to stop the musty odor before it starts.

1. Waterproof critical areas: Seal basement walls, crawl space floors, and bathroom wet zones using cementitious coatings, liquid membranes, and vapor barriers to prevent water leaks and seepage.
2. Control indoor humidity: Keep humidity below 50% using dehumidifiers and exhaust fans, especially in laundry rooms, bathrooms, and crawl spaces.
3. Fix leaks immediately: Repair roof leaks, plumbing drips, and HVAC condensation issues as soon as they appear to prevent hidden dampness.
4. Improve ventilation: Use attic vents, closet air grilles, and mechanical ventilation systems to keep air moving in enclosed or humid areas.
5. Maintain HVAC Systems: Clean ducts, replace filters, and service drain pans regularly to stop microbial buildup that causes a musty odor to circulate indoors.

Is Musty Odor Toxic to Humans and Pets?

Yes, a musty odor can be harmful to both humans and pets, especially when it signals hidden mold or fungal contamination. Prolonged musty odor exposure triggers respiratory issues, headaches, eye irritation, and worsens conditions like asthma and allergies in adults and children. Pets like dogs and cats may suffer from sneezing, itchy skin, or even breathing difficulties. The odor itself isn’t toxic, but the mold spores, mycotoxins, and airborne allergens behind it pose serious health risks when inhaled regularly.

When to Call a Professional Waterproofing Expert

You should call a professional waterproofing expert when a musty odor persists despite cleaning, dehumidifying, or ventilating. At Aqviz, we often step in when homeowners face recurring dampness, mold regrowth, or unidentified water intrusion. If you notice foundation cracks, basement flooding, or humidity above 60%, it’s time for expert inspection.