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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 9:00 AM ET


8 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 10:58 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 11:55 AM 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 1:17 PM ET


Jeff I have the exact same issue we used 20 Mil vapour barrier last June as you we went through winter ok but now we get that smell you described .

We were curious how you made out with your problem

Your help in this matter is appreciated

Regards Gerry Dorion

Answered by Gerry Dorion
Posted Oct 5, 2015 10:45 AM ET


We are having same issue in our crawl space. The company has replaced the dehumidifier but odor still very strong. Any resolutions found to your crawl odor? Grateful for any suggestions

Answered by Jay Bryan
Posted Oct 24, 2015 1:06 AM ET


It's been over 2 years and the smell is as strong as ever.....tried many things and thought of ripping up the barrier altogether. Stopped using the dehumidifier. So what I did is leave barrier intact but reopen a few vents on one side of crawl - note, these are the ones I has sealed before. And on the other side of the crawl I reopened two vents and places good fan ventilators that run all the time. This seems to have kept the odor out of our living space in the house but smell is still there in the crawl. Trade off is the humidity level is same in crawl as outside air so so much for sealing the crawl. I left barrier intact only because before all this nonsense I only had a vapor barrier and the vents were all open. So I am back to square one with the same set up except a better vapor barrier and better sealing and open vents with 2 fans. I am quite sure the smell is coming from the barrier and or sealants but decided if I can manage with the fans I will just leave it be. Hoping the smell eventually disapates but seems to be strong as ever. Very disappointed I have not found a good solution. Many others have this issue by the way. No one has cracked the code. And my crawl is clean, no leaking water, no animals nothing that would cause the smell...except the barrier and sealants and tape used. Jeff

Answered by jeff weikert
Posted Oct 24, 2015 7:58 AM ET


I would suggest finding out what material the vapor barrier is and what sealant was used. For example, vinyl sheets can be smelly as can Tremco acoustic sealant. Polyethylene as a barrier tends to be less smelly, and Contega HF is a sealant that is much less smelly to start and that stops smelling much faster (within hours).

To figure out where the smell is coming from, take a sample of each proposed or existing material, and put it in a glass jar with a tight lid for a few days. Then open the jar and smell it.

Polyethylene is the most common vapor barrier material, and I have yet to hear of anyone finding it smelly. Perhaps a bad batch? You can buy a small package of poly sheeting at a hardware or home store for under $5 and test it to see if it has the same problem for you. If you did find that to be a problem, another inexpensive plastic sheet material that is low smell/taste/toxicity/outgassing is polypropylene. It's harder to find in big rolls of the kind of thickness you'd want, but you could probably find something you could use. Another option might be radiant barrier foil, which is Al foil laminated to a reinforcing scrim. Foil is highly impermeable, so would block any smell from underneath it, and although I don't know what scrim material and adhesive are used, it would probably seal in any smell that might result from that. It would be more expensive than polypropylene, but might be easier to find.

Answered by Charlie Sullivan
Posted Oct 25, 2015 7:17 AM ET



Did the company install open-cell foam as part of the process? Improperly installed foam can give off a very bad odor.

Answered by Steve Knapp
Posted Oct 25, 2015 9:08 AM ET

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