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G Ollis 04-11-2012 10:44 PM

Odor from Crawl Space
Thanks in advance for anyone who can help! :thumbsup:

I purchased a house in central NC at the end of January 2012. During home inspection, we discovered a mold problem on the floor joists. We had a professional company come in and treat, kill, clean, etc. the mold. We also had a conditioned, sealed crawl space installed. The installer used a 20 mil vapor barrier and Thermax(TM) board insulation for the walls of the crawlspace. There are vents and returns along the main trunk line as required by code. The installer placed a humidity monitor in the crawl space that I can check and everything seemed be correctly done.

Now for the rest of the story and my reason for posting...

The next three days after the sealed crawl space was installed was horrible inside my house. There was an extremely strong odor like an earthy, musky smell. The installer thought that it was off-gassing from the materials in the crawl space and possibly the moisture that remained. "Give it a week."

A week goes by and the odor remained. I then placed a squirrel fan at the crawlspace door blowing out. The fan remained for about 5 days and the smell seemed to lessen. The installer placed a dehumidifier in the crawl space and said give it a little while longer.

Two more weeks, the smell lessened more but still was noticeable. As it was an unusually warm March in NC, we moved our stuff in the house and opened the windows to air it out. The heat was off during this time. Meanwhile, the installer taped the crawl space vents shut and installed a vent fan blowing out of the crawl space. Over the next few weeks, the odor appeared to be getting better. However, when a cold snap came through, the windows had to be shut and the heat turned on. The smell returned. The installer made sure all HVAC ducts were taped, the vapor barrier was rechecked, and the floor vent boots were sealed with a puddy that hardens from the crawl space side of the boot to limit leaks into the house.

The smell is still very noticeable inside my house. If you go to the vent fan blowing out, the smell is much stronger due to the concentrated air blowing out of the crawl space. We have triple checked the floor joists and they are bone dry (no moisture problem there). The humidity levels inside the crawl space and house are normal if not a little on the dry side (around 30-40 RH). We cut a small place in the vapor barrier and checked the soil under it, it too is dry and does not smell out of the ordinary. The HVAC ducts have been fogged, cleaned, and the coils cleaned on the unit. There is not any standing water anywhere in the crawl space.

I am my wits end here! Here are the facts I can tell you:

1. The floor joists had mold on them before the sealed crawl space was installed but there was never any smell inside the house before the conditioned crawl space was installed.
2. The HVAC ducts remained after the cleaning of the mold and were not replaced.
3. The odor was the strongest 1-4 days after the install but still remains.
4. To the best of my knowledge, there is NOT a moisture problem in the crawl space.
5. We have tried HEPA filters and an Ozone generator inside the house but not in the crawl space.
6. The installer did a follow up air quality test and there was less than the average household mold or spores in the air.
7. The odor seems to be worse when the heat is turned on.
8. The vent fan outputs this strong smell whether the HVAC is on or off.
9. We have taken samples of the vapor barrier, Thermax, and floor joists; none of which seemed to produce a smell when placed in a container and allowed to heat up with outside heat.

Thanks for taking the time to read, please let me know if you have had a similar experience or can offer any suggestions!


Gary in WA 04-12-2012 12:22 AM

Welcome to the forums! Did you do a "Search" in the white box at top of every page, here? I did a quick check:

This was interesting, what brand is your v.b.?


G Ollis 04-12-2012 12:53 PM

® 20 Mil Reinforced is a multiply laminate combining U.V. stabilized film with a high strength cord grid. It is specifically engineered to provide high strength and durability in a lightweight material.

Also my installer checked the crawl space today and thought the smell was similar to cat urine. It might be, I don't know. Could this be off or out gassing?

DangerMouse 04-12-2012 02:14 PM

Rodent urine can smell quite similar to feline/canine urine.


Big Stud 04-12-2012 03:30 PM

I am not even gonna ask how you know that DM, :lol:

DangerMouse 04-12-2012 04:00 PM

Hmmmm.... we have cats and we have mice in the chicken coop and my daughter has pet rats.
I have no idea how I'd know that!


G Ollis 04-12-2012 06:31 PM

Thanks for the replies, but I am sure that rodents are not the problem. We do not have a dead animal smell or any signs or rodents. The crawl space is sealed and conditioned but thanks for the suggestion. At this point, we are going to run the air condition this weekend to see if the smell goes dormant due to the cool temperature (i.e molecules slow down with cold and speed up in heat). If it does go dormant, then off gassing is most likely the culprit, if the smell remains, then the HVAC air ducts are getting replaced.

Please continue to post any other ideas or similar situations you may have. Thanks,

G Ollis

Gary in WA 04-12-2012 11:33 PM

What did they use to treat the mold?

If not too extensive, you could paint the joists with Zinzer (sp) 123, or similar to block it completely.
Ever had a water leak in a bath/laundry, with water getting into the supply duct/register to mold on the debris there....


joecaption 04-12-2012 11:50 PM

Close to what I was going to suggest.
A simple wax ring under a toilet can cause the smell.

Maintenance 6 04-13-2012 06:42 AM

Is there any fiberglass ductwork in or around the mold remediation area that could have gotten wet from the mold clean up?

Did the company take an air sample right at a supply diffuser (vent) with the air handler running?

Did they sample for anything other than particles? Any gas detection sampling such as formaldehyde, VOCs or other?

Is the mold remediator also taking the air samples?

If yes, have you considered using an independent air monitoring firm?

John_W 04-13-2012 04:59 PM

Possible causes:

1. Caused by the work/materials done/added to your crawl space. Suddenly you go from no-smell to smell just as they finish the work.

2. You said that someone thought it was a urine-like smell. So, that's also a possibility.

If, when you explore around in the crawl, you find that the smell seems to be concentrated in one area, it's more likely to be of urine or dead animal origin.

If it smells the same everywhere, then that work you had done seems more likely to be the cause.

I have been dealing with a urine smell in my crawl for a couple of years now. I have a radon mitigation system in my crawl, plus new HVAC furnace/coil/ductwork. The smell started about a year or two after all that work - and seems to have had some rodent activity as the source.

I tried all kinds of stuff to eliminate the odor. It's mainly a problem now in the warm, humid summer months.

You can read all the details (with many pictures) here:

Check out the second page, near the bottom, for a summary.

What helps me the most is hanging three bags of Earth Care’s Odor Remover near the place where the return air duct meets the HVAC equipment. The odor seems to be getting into the HVAC system at that junction, even though a smoke test reveals no hint of a leak. The bags suck up almost all of the smell before it can get into the HVAC system.

If you can keep the HVAC system from sucking the smell into your ducts, with these bags, maybe you can breathe a little bit easier.

Here is a link to the odor eliminator bags:

Good luck.

G Ollis 04-14-2012 08:56 AM

John W.

Thanks. I have read your post before. The smell did not start until after the work was done and the smell is all around in the crawl space, not a certain spot. The smell began immediately after the mold problem was addressed.

Thanks again.

G Ollis

DangerMouse 04-14-2012 11:57 AM

Look around down there for the jug of urine the workers left.


John_W 04-14-2012 05:34 PM


Originally Posted by G Ollis (Post 898651)
John W.

Thanks. I have read your post before. The smell did not start until after the work was done and the smell is all around in the crawl space, not a certain spot. The smell began immediately after the mold problem was addressed.

Thanks again.

G Ollis


About replacing your ducting:

Have you opened the system, say at either end of your HVAC equipment, and sniffed inside, while the blower was off? If the smell in the crawl is coming from a compromised duct system, it would probably smell much worse inside the ducts than it does in the rest of the crawl.

WillK 04-14-2012 08:25 PM

Okay I'm confused. On one hand you say that a company made your crawlspace conditioned and sealed. But you also describe vents. These are two mutually exclusive terms - the crawlspace is either sealed or vented.

Read this

Is there or was there any insulation in the floor joists over the crawlspace?

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