Short answer: a musty basement smell almost always means moisture. Find and fix the source first: leaks, poor drainage, high humidity or a past flood. Then dry the space with a dehumidifier, and clean the carpet, rugs, upholstery and other soft materials that absorbed the odour. Air fresheners only cover it up.
Common sources
- High humidity: basements are cool, and warm summer air condenses on walls and floors.
- Small leaks: foundation cracks, window wells and plumbing leaks.
- Past water damage: carpet and pad that got wet and never fully dried.
- Poor drainage outside: downspouts and grading that send water toward the house.
- Stored items: cardboard boxes, old clothes and fabric that hold moisture.
- Dirty ducts: basement return vents that pull in damp, dusty air.
Step by step
- Find the source. Check walls, floors, corners, under stairs and behind storage for damp spots, stains or visible mould.
- Fix the moisture. Seal leaks, redirect downspouts and repair plumbing.
- Control humidity. Run a dehumidifier and aim for about 30 to 50 percent.
- Clear the clutter. Move items into sealed plastic bins and off the floor.
- Clean soft surfaces. Carpet, rugs, upholstery and drapes hold odour.
- Improve airflow. Keep doors open and run fans.
When carpet is the problem
Basement carpet sits on cool concrete and often absorbs moisture. If it got wet in the past and was not dried properly, the pad underneath can hold the smell. Hot water extraction and odour treatment fix most cases. If the pad is badly affected, replacing it is often the real fix. See odour removal.
When to call a specialist
If you see mould on drywall, framing or ceilings, or the smell persists after drying and cleaning, have a mould remediation specialist assess it. If water keeps getting in, a waterproofing contractor can help.
Measure the humidity first
A musty smell is almost always tied to moisture. An inexpensive hygrometer from a hardware store tells you the relative humidity in the basement. Aim to keep it below about 50 to 60 percent. If it is higher, a dehumidifier sized for the space, with its bucket emptied often or drained to a floor drain, makes a big difference. Check readings in summer especially, when warm outdoor air meets cool basement walls and moisture condenses.
Where odours hide in a finished basement
- Carpet and pad that got wet once and never dried fully.
- Drywall and baseboards along exterior walls.
- Boxes, fabric and old furniture stored against the walls.
- The floor drain, if its trap has dried out and lets sewer gas in. Pour water into it once a month.
- The sump pit, if it has no tight cover.
- Return air ducts that pull basement air into the rest of the house.
Long-term fixes
Deal with the source of moisture before treating the smell. Clear eavestroughs, extend downspouts, and make sure soil outside slopes away from the walls. Seal cracks where water seeps in. Run the bathroom fan in the basement and avoid drying laundry indoors. Once the space stays dry, a deep carpet cleaning with odour treatment, cleaned ducts and fresh air usually remove what is left. If you see mould growing over a large area, have it assessed by a mould remediation professional.
Freshen up your basement
UltiClean deep cleans basement carpets, treats odours and cleans ducts across Toronto, Vaughan, Richmond Hill, Aurora and Newmarket. Call 647-676-0576 or see deodorizing and odour removal and carpet cleaning.
Musty Basement Smell FAQs
Does a dehumidifier get rid of the smell?
It removes the moisture that causes it, but soft surfaces that absorbed the odour still need cleaning.
Will baking soda work?
It absorbs some odour on the surface, but it does not reach the pad or fix the moisture.
Can duct cleaning help?
If basement returns pull in damp, dusty air, cleaning the ducts can help. See is duct cleaning worth it.
Is a musty smell dangerous?
It means there is moisture, and possibly mould, which can bother people with allergies or asthma. Fix the source and talk to your doctor if you have health concerns.
What if the basement flooded recently?
Read flooded basement carpet: what to do first.
Musty basement in Toronto, Vaughan, Richmond Hill, Aurora or Newmarket? Call UltiClean at 647-676-0576.
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Written by
Carpet, air duct and tile cleaning specialist at UltiClean
Seyedamir (Amir) Vafamand has 12 years of hands-on experience cleaning carpets, upholstery, air ducts, dryer vents and tile and grout in homes across Toronto, Vaughan, Richmond Hill, Aurora and Newmarket. This guide is based on that work.
- 12 years of experience
- 1,100+ jobs completed on Jiffy
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