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Strong odor after crawlspace encapsulation

We had our basement encapsulated in the fall last year and made it through winter no issues. They used a thick mil high quality (apparently) vapor barrier and then sprayed /fogged with mold preventative. I don't think there is any more mold - smell is not musty really and I don't get a mold allergy reaction.

We live in a 50 year old brick ranch in Atlanta GA. Now since Spring we are smelling this bad smell. It is making me sick I believe. It smells a bit like cat urine type smell..... I have tried air cleaner, odor remover etc. with no luck. Basement is dry and at 40 percent humidity so dry. I have a dehu running as needed down there. Our furnace/AC and gas water heater are all in the crawl space as well. So we have those venting out I am hoping the smell eventually dissipates but so far it is strong and we smell it in the living space when the AC runs. A subtle yet bad smell. What to do??? I spent a lot on the encap. Didn't anticipate this bad chemical-cat urine-odd smell.

I am worried it is toxic. I don't know how to proceed. Recently had ducts professionally cleaned. Have had 2 HVAC guys checking duct connections and AC. Everything normal they say. Except the strong smell. I am pretty disparate for a solution. The crawlspace guy who did the encap said he never had any complaints about a smell....except early on he got one and he changed the material used afterwards.

Thanks. Jeff

Asked by jeff weikert
Posted Jul 22, 2014 10:00 AM ET


3 Answers

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In my opinion, you may simply need to ventilate the area (install an air exchanger or place a fan in a window) for a while and see if that makes a difference now that the area is sealed tightly. Plastics in general emit some nasty by-products which need to be ventilated to the outside of the building. If this does not work you can order an air quality test to see if you have mold and also to check what level your total volatile organic compounds are at. Should the test come back as unacceptable (red zone), you may need to bring in an environmental engineer to find a solution for you. Typically ventilation will correct your problem. You may also consider testing the home for radon while your at it. Radon suction ports installed below the membrane will also eject emitting odors to the outdoors.

Here's a simple DIY test to start with;

Answered by Richard Beyer
Posted Jul 22, 2014 11:58 AM ET


1. You said that you "have had 2 HVAC guys checking duct connections." But you didn't tell us whether your duct seams have been sealed with mastic. Did anyone perform a Duct Blaster test to check for duct leakage?

2. Sealed crawl spaces can be conditioned one of two ways: either by including a register connected to your forced air system, or by installing an exhaust fan in your rim joist to depressurize the crawl space (as well as a floor grille to connect the conditioned part of your house with the crawl space air). If you choose the latter approach, you are more likely to prevent any odors from entering your house. For more information on what I'm talking about, see Building an Unvented Crawl Space.

Answered by Martin Holladay, GBA Advisor
Posted Jul 22, 2014 12:55 PM ET


Jeff, does any part of your home insulation include cellulose? It's a great material but I have heard of errant batches which have been incorrectly treated with ammonia, leading to the pervasive cat urine odor. In the case with which I'm familiar the supplier of the faulty material bore the cost of removal/replacement.

Answered by James Morgan
Posted Jul 26, 2014 2:17 PM ET

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