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The Harsh Reality of Offgassing in an Encapsulated Crawl Space in Hendersonville, Asheville, Western NC & Upstate SC



The heavy mil plastic that some of these companies use to encapsulate the crawl space often off gas terrible odors that are often reported right after the install. These odors have been described by many homeowners in multiple states, mostly in the South, as smelling like cat urine.


Plastics and Outgassing

This topic does come up occasionally, especially when discussing the use of industrial plastics in high heat environments or in closed spaces. So what exactly is “outgassing”, also termed “offgassing”? Most plastics contain volatile organic compounds (VOCs). These can be poisonous, carbon-containing chemicals that are volatile enough to evaporate even at room temperature.


The Smell Factor

PVC, or Polyvinyl chloride, is one of the best known plastics for its odor. These outgassing odors are most noticeable with new PVC products, but they diminish over time. For example, a shower curtain made with PVC can outgas for a month or longer and high temperature and humidity tend to speed up the process. Certain plastics when placed in “closed environments” like a crawl space, can outgas for much longer periods.

Don’t be fooled, there is a difference in what materials you use to have your crawl space encapsulated and conditioned. The wrong plastic liner can become more problematic than the dirt floor you had before. Closing your crawl space vents to the outside temperatures, sealing the inside with the “right” liner, and conditioning the space is absolutely the “right” thing to do for the health of your family and your home. 

At Basement & Radon Solutions, we have many years experience in crawl space encapsulation and implement a proven solution with the best liner available that will never outgas harmful VOC’s. Your family’s health and safety is our top priority!


But, don’t take our word for it! 

Read more published reports:


Green Build Advisor

Strong Odor After Crawlspace Encapsulation

We live in a 50 year old brick ranch in Atlanta GA. 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. 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. 

Thanks. Jeff



We are having the same problem in Washington DC. We had to dig out a dumpster worth of soil in our crawl space in order to run pipes. We then encapsulated with 12 mil Dura Skrim on the bottom and spray foam on all four walls. This was 6 months ago and when we moved in mid-October the smell was permeating the 1st floor. It is a cat urine smell. The crawl space is very dry, 50% humidity, and no rodents. I have had four different crawl space companies and the company that encapsulated come to inspect the smell and no one knows what it is. 

Answered by Melissa Martin


I am experiencing the same issue of a cat urine smell in my encapsulated crawl space in the Atlanta area. I started by contacting the installer, which contacted the manufacturer of the polyscrim material used as the vapor barrier. No luck there... The manufacturer said they didn’t have issues and said its more than likely offgassing of the soil. As a temporary solution I opened up 2 of my crawl space vents and installed vent fans to get some air movement. It helped a little, but still not happy with it. Especially since I opened the envelope to my encapsulation. Has anyone successfully removed the “cat urine” smell??

Answered by Mr L3B


©2015 Green Building Advisor. From The Taunton Press, Inc., publisher of Fine Homebuilding Magazine

Read more: 



Odors and Smells in Encapsulated Crawlspaces


Published on August 26, 2016

Michael Masserang

Owner at Masserang Consulting 


• Construction materials such as wood members, insulation, plastic, the acidity in the soil, etc. all off gas odors, and these odors can percolate up into the living areas.


• HVAC systems that are installed inside the crawlspace using natural gas can also be a challenge inside a sealed crawlspace especially if it is not properly vented at the time of construction.


• The heavy mil plastic that some of these companies use to encapsulate the crawlspace often off gas terrible odors that are often reported right after the install.


• If there are currently any biofilm contaminants infesting the floor joists, insulation, or subflooring, these fungal or mold colonies also off gas odors that can now percolate up into the living spaces.


• If the crawlspace was encapsulated with a drainage problem, moisture can build up under the liner and cause the development of mold which off gases odor that smells like cat urine. This is a huge problem as most companies do not install foundation drains when they encapsulate.



Find out how you can get a clean, dry home with our dehumidification systems by contacting Basement & Radon Solutions at 828-759-5522 for a free estimate!

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