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Community and Q&A

Cat urine odor in crawlspace

Roberto450 | Posted in General Questions on

Hey guys would like some feedback on how to best address cat urine odor in our crawl space. History: NC house built in 1981 remediated in 2016 due to water leaks causing mold. Hand sanded all boards in crawl space discarded porous items ect.. Vapor Barrier 20Mil polyethylene encapsulated entire crawl space with Sante Fe DU unt. Two family members with chronic illness so trying to address the root cause of the problem. As we know there appears some controversy on what exactly is causing the odor. Is it the decay from the soil contaminates triggering a ammonia smell due to a rising ph well above 7 ?? Or is it the material of the vapor barrier itself (polyethylene) when it becomes weak exposing the cord resulting in the smell.There appear to be two options. 1. Install a exhaust fan in the crawl space to eliminate the odor but not the bacteria decay that could be causing our symptoms which are teary eyes, dry noses, & a rash. Cost approximately 750.00 dollars installed. Option 2 : Remove our current vapor barrier & install a MBR (Moisture radiant Barrier) aka Radiant Barrier Insulation Liner which (supposedly) would eliminate/eradicate the bacterial decay that is causing the ammonia which may be entering into the house triggering our symptoms. Approx. cost $5500.00 . In closing addressing the root cause is my goal. The question to the group will the new radiant barrier insulation liner eliminate the smell in conjunction with the bacterial decay ? Hopefully the end result would be to completely eliminate our symptoms. I would most appreciate any thoughts or suggesstions given the current situation. Thanks Guys !!!

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  1. Expert Member
    Dana Dorsett | | #1

    It's highly unlikely that any reaction with polyethylene will create ammonia. It's probably just not sufficiently air tight.

    Pouring a 2" rat slab over the existing 2o mil polyethylene vapor barrier should take care of anything happening at or under the vapor barrier.

    Depressurizing the crawlspace with a small continuous exhaust fan will prevent stagnation in the crawlspace air.

    1. Roberto450 | | #5

      Thanks Dana for your reply. I’m beginning to think the mild cat pee odor is from the decay in the soil under the vapor barrier. My Q for you would the 2” rat slab over the 20 mil take care of not only the smell but the Residual effect of the decay that could be permeating throughout our house ? if the ph of the soil is above 11 wouldn’t putting sulfur on top of the dirt Neutralize/reduce the ph to around 7 ? If so this may solve any future decay as we have symptoms of a teary eyes, rash, & dryness in our noses Approximate cost of 2’ rat slab installed ? Total Sq. ft of house is 2250. Also awaiting results of ERMI regarding mold. Thoughts ?? Once again thanks for your help.

  2. Expert Member
    BILL WICHERS | | #2

    I sure hope that $5500 “liner” includes installation labor! There is no point in a radiant barrier in a crawl space liner. I’d just use a 10 mil or thicker polyethylene liner. 12 and 20 mil products cost more but hold up better. Americover has lots of options.

    If your existing liner looks ok (no holes or cuts), try using a sponge mop with a bleach solution to disinfect the liner. You might be able to clean it and solve the problem. Polyethylene itself is pretty impervious and won’t soak up anything spilled on it, so anything that smells is most likely just something on the surface.


  3. Andy_ | | #3

    In my experience of repair work on enough homes the "cat urine odor" is almost always a sign of rats. They may have already moved on, but the rat pee smell lingers and the dried rat poop and pee can cause the physical symptoms you describe. I know that I have a bad enough reaction to it that I won't go into a crawl or attic like that without fully suiting up in a Tyvek suit and putting on a full respirator.
    The rat droppings are often in the insulation and along the foundation sill. Pull back the insulation and see if there's any sign of it. If you have rats, get rid of them, then make sure their buddies can't get in, then clean clean clean. Air seal and re insulate and lay down clean polyethylene.
    I hope it's not rats, but if it is then at least you'd have a course of action.

  4. Roberto450 | | #4

    Hey guys thanks so much for your responses. I'm in the process of checking my soil ph underneath our vapor barrier. Is anyone aware of a crawlspace test that would also include gases such as methane, ammonia ect.. Just want to rule it out. Thanks again

  5. MSVA | | #6

    Was the crawlspace/foundation ever treated with a chlorinated insecticide for termites in the 80s? It was pretty common in 70s/80s. Chlordane is now banned because it does not degrade well. Just wondered if residue is reacting with the plastic. New carpets react with chlorine dioxide in tap water to cause cat pee odors in the air. Kind of weird but it happens. Just wondered because we have same smell and know there's pesticide residue. Just asking different people to see if this is a commonality - Pre-1990s home, previous termite treatment with chlorinated pesticide, plastic vapor barrier....
    This is link to tap water/carpet 'cat pee' smell.....

  6. ElroyJ | | #7

    Did you ever test ph in your crawl space. I had my craw space encapsulated with 12 mil Amaicover Dura Skrim and have a very strong amonia cat pee smell. If you are able to fix the ph does this guarantee that it will not need to be retreated after the barrier is back in place.

  7. ARnurse | | #8

    Curious to see how this works out—I just installed a 10mm vapor barrier and trying to figure out the cause and treatment. I’m beginning to think think it’s more common than people think.

    Great thoughts on the old termite chemical.

    I’m curious on ph treatment. I’ve found exhaust fan helps some—I’m sure soil gas mitigation would work—and be symptomatic treatment.

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