Crawl Space Odors

Should you leave the old vapor barrier and debris behind when performing crawl space encapsulation? Can leaving old vapor barrier and debris be causing odors? We had a great Ask a Ninja from Georgia and wanted to share our thoughts:

“I purchased a home in March which had mold remediation and a 20 mil Dura Skrim vapor barrier installed (ground only). A Sante Fe dehumidifier keeps humidity in the high 40’s; there are 2 open vents out of 9 in a 1400 sq ft space; no active vent fans. The crawl space smells, but not like cat urine. I believe it to be soil off gassing and it gets pulled into the HVAC. Can CSN add-on to my existing (newish) 20 mil barrier to complete an encapsulation or must we start over?”

Crawl Space Odors – Cat Pee

Not every odor you find in the crawl space smells like cat urine. Cat urine odors are prevalent in many crawl spaces. Crawl space encapsulation is not a guarantee your crawl space will not smell like cat pee. We feel the biggest reason for cat urine odors in crawl spaces is cheap reinforced vapor barrier. If you recently had the crawl space encapsulated with reinforced vapor barrier consider removing and replacing the plastic.

Crawl Space Odors – Soil Gases

Crawl space odors can also come from under the plastic and the odor can be hard to identify. Many homeowners want us to leave down the old vapor barrier. This can be a problem if the old vapor barrier was ever exposed to sewage or moldy debris. Most will not take time to wipe down the plastic before installing new plastic on top. trapping odors between plastic can create a hot bed for more bacteria. More bacteria can become more odors after crawl space encapsulation.

Debris Under the Vapor Barrier Causes Odors

This is one of the biggest overlooked items when dealing with crawl space odors. The debris under the plastic vapor barrier can grow mold, wood rot fungus, bacteria and slime molds. The percolate together and off gas some powerful odors. make sure you remove as much loose organic debris as you can prior to installing vapor barrier.

Will radon Mitigation Lower Humidity

Do you need help battling an odor in your crawl space? If so, please contact Crawl Space Ninja and we will be glad to help. Also, let us know in the comments below if you’d like to suggest a future blog post.

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6 thoughts on “Crawl Space Odors”

  1. Hi Michael,

    What might be the cause of our crawl space liner to be billowing? This appears to be in correspondence to a slight odour and the liner has numerous air pockets underneath, whereas the liner used to lay flat. 🤔


  2. Hi Michael,

    I purchased my home in October of 2016. Had fiberglass insulation in the floor joists but with the humidity a lot was wet / sagging, just in bad shape. I removed all of the insulation and fully encapsulated the crawl space and added a dehumidifier both in 2017 / 2018. A few months ago we started noticing a smell in the HVAC, when the air handler fan is running. It’s not mold, cat pee or any of the usually suspects but it smells horrible. I had my HVAC ducts professionally sealed about 4 years ago as well. I added 4″ perforated, corrugated pipe under the vapor barrier and added a soil gas mitigation fan (outside the house) as well opened up two of the vents (opposite corners of the crawl) and installed an intake and exhaust fan. Nothing has worked, I still have the smell. I have since removed the intake fan and left the exhaust fan. I faintly smell the odor in the crawl space when I’m under there but not like when it comes through the HVAC vents. Any ideas / suggestions on how I can remedy this? It’s driving me nuts and I’m at a loss for solutions.

  3. Hi Michael,
    We purchased our Lowcountry South Carolina (high humidity) house last September and shortly after that started noticing a strong cat pee smell. Previous owners had the crawl space fully encapsulated with a dehumidifier installed in 2017 so we had the company who did the work come out to inspect and they discovered the dehumidifier wasn’t working so replaced with new unit with hopes in 30 days or so the smell would go away. It eventually did but reappeared about 3 weeks ago causing me to think it’s seasonal based on outside temps and humidity, not faulty equipment. The company came back out today and are suggesting installing a radon fan that will extract air from under the encapsulation plastic and push it outside of the crawl space. Do you see this as an effective option? We’re waiting on their estimate but can assume it will be pricey. To save money, is having a simple exhaust fan installed to pull smell out of crawl space an option or does that negate the “encapsulation” factor?
    We look forward to your response. Thank you!

    1. Hi David, if the source of the odor is the vapor barrier, usually adding exhaust fans will not take care of the problem. We find cat pee odors in crawl spaces with debris under the plastic and sometimes the plastic itself is a cause if it is multilayer and separates. This allows moisture to enter between the layers. Our only solution we have discovered is remove/replace multilayer plastic and remove debris under the plastic in the process. Hope that helps.

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