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Cat [urine] smell coming through return vent after Crawl Space Encapsulation

Cat [urine] smell coming through return vent after Crawl Space Encapsulation

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  #1  
Old 10-05-14, 05:36 PM
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Cat [urine] smell coming through return vent after Crawl Space Encapsulation

During the Summer of 2013 we noticed that the hardwood floors on our first floor would cup during the summer. We live in the Charlotte NC area. Our house is on a crawl space that was vented. After many hours of research I determined that the floor cupping problem was probably being caused by humidity in our crawl space. Our house just had a basic vapor barrier that wasn't installed correctly.

I hired a company in the Fall of 2013 to encapsulate my Crawlspace. They did a fantastic job of fully encapsulating my crawlspace, installing a dehumidifier and a sump pump. The Sump Pump has about 15 feet of French drain that empties into a bucket.

A few weeks after the work was completed I noticed that we started to get a smell in our house and I narrowed it down to the return vent on the first floor. I did not notice it as much when the HVAC system was running but it was much more noticeable when not running. I could also smell it out of some of my vents but not much.

I first siliconed all of the vents on the first floor to prevent the HVAC from pulling any air from the crawl space. This did not help much so I then called a local HVAC company. I had them pull duct box for the supply vents to see if there was any mold. This box was insulated from the inside and there was a little bit of mold. I had them rebuild this box and to make sure that everything was sealed up well.

Smell still did not go away.

I then had them rebuild the return plenum box and seal it very well with mastic. They also sealed the return box (where the filter goes) with mastic to ensure that no air could enter through the box.

Smell still did not go away.

I then red a story about other people that had this issue and they used a Radon fan to pull air from under the vapor barrier and extract it from the house. Here is the article: Crawl Space Soil Gas

I ran 100 plus feet of PVC created 4 openings in different areas in my crawl space so I could remove air from underneath the vapor barrier. This worked great and we rarely smelled what we had smelled before.

It has been about 9 months since I installed the radon fan and piping and we are starting to get the smell again more often.

I cannot figure it out. The only thing that I have not done is to replace the flex duct for our supply vents.

The only think that I can think of is that maybe the smell is coming from somewhere within the flex duct and it is coming back through the HVAC system when it is off and through the return vent. I can barely smell this odor from the supply vents so this may bust my theory.

Oh, I also cleaned my coils and replaced the PVC condensation pipe.

What is this odor? Any help is appreciated because I am at a loss.
 

Last edited by ray2047; 10-05-14 at 07:37 PM. Reason: Change p*** to urine in title.
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  #2  
Old 10-06-14, 02:13 PM
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Anyone experienced anything like I described? Or, do you have any other ideas about how to solve my problem.
 
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Old 10-06-14, 06:07 PM
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How does cat urine fit into the story? Have you determined that the smell is cat urine? If you are sure of that, it is just about impossible to eliminate it.
 
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Old 10-07-14, 12:43 AM
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I probably should have left that out of the title even though the odor is similar to cat urine. The odor is NOT cat urine and certainly not the point of the story. I am just trying to figure out other ideas about how to eliminate the odor that is coming our of our return vent.
 
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Old 11-14-14, 12:10 AM
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Have the exact same situation here. HVAC guy came out cleaned coils, no help. I don't think cleaning ducts would help, since the smell definitely is the return air system. I had not connected it with the crawl space encapsulation job. But it did start after the encap job. I am going to call them and see if they have seen this problem occur in other homes.
 
  #6  
Old 11-19-14, 02:52 PM
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Odor resolved

Contacted our encap guy. He contacted his company. Not a common problem. The smell seems to occur most often in encapsulation jobs done on the east coast in rural areas. The ground contains materials that are decomposing and releasing gases through the drain tile. This odor can travel through the liner and then the return air vents pull it into the house. The problem is solved by using a venting system like you would for radon gas. Will cost a few bucks but I am glad there is a remedy for the smell.
 
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Old 11-21-14, 02:19 PM
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i'm unsure what causes that issue but, coincidentally, a caller last saturday mentioned the same issue to the show's guest who, it turned out, had done the work for her,,, she also broadcast she had googled the issue & found many others experiencing the same odor,,, i'd hazard a guess its the membrane outgassing,,, we've never had any trouble w/stego - not even a camel or goat fragrance

ps - wait a few yrs & you'll find vents are supposed to be open, NOT sealed - no one really knows,,, i have mine open w/fans on 1 side controlled by a humidistat
 
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Old 01-13-15, 01:43 PM
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Any update on this issue? I was about to encapsulate my crawlspace due to high humidity and slightly elevated radon but then ran into a neighbor who had experienced the "cat urine" smell after having vapor barrier installed in his crawlspace. After reading online about this issue, i see where many others have had the same issue, so i put my install on hold.

I have seen many say they don't know what causes it but have seen others guess that it is caused by a reaction between the dirt/soil and the plastic vapor barrier. I have no idea if this is accurate or not but would love to hear what's going on and how to avoid this situation. I had one radon/encapsulation company say that he was called for second opinion and eventually hired by someone to try to fix the cat urine smell which developed after encapsulation and so he installed the radon suction under the plastic vapor barrier creating negative pressure, so that the air under the plastic, and any bad smell associated with it, is removed from the crawlspace before it gets up into the house. He said this worked but only time he has had to deal with it. He felt it was happening because the encapsulation company was using some sort of cheap plastic from china.
 
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Old 01-13-15, 01:46 PM
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db321 - welcome to the forums. Your question was answered in post #6.
 
  #10  
Old 01-13-15, 07:28 PM
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mitch, was hoping the original poster would post whatever happened to his situation. Is there a way to contact a particular poster...like ez message or something?
 
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