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Crawl Space Smells – 4 Areas to Check

Is your crawl space suffering from odors? Whether the odors came after crawl space encapsulation or before, here are some places to look and advice on what to do.

  1. Above Floor Joist Insulation
  2. Reinforced Vapor Barrier Installed
  3. Debris Under New Vapor Barrier
  4. Crawl Space Not Ventilated Properly

Odors Trapped Above Floor Joist Insulation

If you have fiberglass batts, rock wool, or spray foam insulation installed in your sub-floor. They can all trap moisture and odors. I have removed lots of insulation with mold and moisture trapped behind them. Rodents and other pests also like to nest there.

If you are experiencing odors, look behind insulation around toilets and other plumbing fixtures. If they are leaking, a slow drip may not be enough to see in the crawl space. But slow leaks can be damaging to your sub-floor while creating lots of crawl space and other home odors.

Cat Pee Odors in Crawl Space

We have removed lots of reinforced vapor barriers from crawl spaces. The main reason is because the crawl space contractor did not properly install the plastic. The second reason is many reinforced vapor barriers can give off a cat urine odor.

Just because the manufacturer guarantees no cat pee odors for their reinforced plastic does not make it so. We have removed reinforced vapor barriers with no odor guarantees. The manufacturer did not pay our labor costs to remove and replace the barrier.

Debris and Old Plastic Under New Vapor Barrier

Did you hire a contractor to install new plastic in your crawl space? Did they remove the wood, debris, and old plastic before installing the new plastic? If not, odors can build up under the new vapor barrier. Many of the crawl spaces we have redone have this problem. When homeowners choose inferior contractors based on price, this can happen.

Other articles of interest

Why Does Crawl Space Humidity Spike After Encapsulation

Is Spray Foam Good for My Crawl Space Floor

5 Problems to Fix in Your Crawl Space ASAP

Should I Remove Insulation from My Crawl Space

Remove Stale Air in Crawl Space

According to the Environmental Protection Agency, crawl spaces are great places for radon, soil gases, and other odors. Crawl space contractors normally ventilate the crawl space or control humidity. The best solution is to do both. Controlling crawl space humidity while ventilating is best. Moving soil gases and odors from crawl spaces is vital. Moving 1CFM of air for every 50 square feet of crawl space is recommended according to the EPA.

Do you need help fixing your crawl space or basement? If so, we can help. Please contact us to schedule your assessment. Also, let us know in the comments below if you'd like to suggest a future blog post.

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About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. Karah Mom on May 8, 2023 at 11:03 pm

    What if I have a vented dehumidifier it filters and I have it vented with duct like my drier is that considered vented for soil gasses?

    • Michael Church on May 19, 2023 at 9:07 pm

      I’m not sure. The EPA recommends minimum 1 CFM of constant air per 50 square feet of crawl space. Does your system meet that minimum? Also keep in mind, its a minimum. More may be needed depending on the amount of soil gases present.

  2. Ann Schaltenbrand on December 1, 2023 at 1:31 pm

    Love all your videos & information. Need help as new house build in 2023 with no vented crawl space, IL required. Clay soil & high water table. Original dehumidifier installed improperly draining 18” from unit into soil/rock 2” deep covered with thin plastic & black tape. Condensation never exit foundation. After 2yrs identified problem then encapsulated but noted wood left under barrier. One month later an odor in crawl space of 2500 sq ft permeating into house. Have been unsuccessful in identifying cause so can eliminate as concerned could be a health issue. Appreciate any assistance in this matter.

    • Michael Church on December 1, 2023 at 1:38 pm

      Hello, it may be a combination of wood trapped under plastic and the plastic itself causing the odors. Can you send me images of the plastic or tell me if it is a reinforced or multilayer plastic? Images can be sent here: https://crawlspaceninja.com/ask-a-ninja/

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