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Chemical smell in a new construction crawl space

Hi folks, great site.

I have a crawlspace in a new house that smells of chemicals. The dirt floor is sealed with a vapor barrier and the walls have Spray Foam Insulation. The space is pretty airtight.

My ERV was installed incorrectly (another story) and sometimes the smell from the crawlspace comes up into the house. Makes my eyes burn, and it gives me a headache. Hopefully that will be fixed this week!

Should I be able to smell the foam 2 months after it has been installed?

How can I tell if I am jumping to the conclusion that it's the foam and not something else, for example floor stain off gassing that never left the crawlspace.

It's pretty scary to think that my new home could be toxic, and I don't want to overreact.

Suggestions on a good path to follow to check things out would be greatly appreciated.

Asked by Brett Michaels
Posted Sep 1, 2014 9:26 PM ET
Edited Sep 2, 2014 6:22 AM ET


6 Answers

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There are three issues here.

Issue #1: Is your spray foam smelly? If it is, you may have a major headache on your hands. For more information on this issue, see Spray Foam Jobs With Lingering Odor Problems.

Issue #2: Is your ERV correctly installed? You provided no details on this problem -- only a tantalizing mention that there is a problem. If you understand this problem, it's time to correct it. You don't want your house to have a ventilation system that makes things worse.

Issue #3: Does your sealed crawl space meet code requirements? Sealed crawl spaces can word just fine, but the building code requires a certain amount of air exchange for these spaces to work. In your case, the best approach would be to install an exhaust fan in the rim joist to despressurize the crawl space. For information on sizing the fan and installing it in a code-compliant manner, see Building an Unvented Crawl Space.

Answered by Martin Holladay, GBA Advisor
Posted Sep 2, 2014 6:29 AM ET


Thanks for your response!

#1 My spray foam doesn't seem to be smelly, but the crawlspace does have a strong chemical odor. I have tried to pull off pieces of it and it doesn't 'smell like anything, but there could be a spot that does smell that I have not found.

My question is, who would be qualified to test the foam?

#2 The ERV is simply not connected properly. It's turned of now, because it was pulling stale air from the basement directly (no duct attached) and passing intake air into the living room. Since the air crosses at the filter, some of the smelly crawlspace air was being sent into my living room. I turned it off until it's fixed.

#3 Not sure about the code. I am going to check into that. The space doesn't have an exhaust fan, but it does have a vent between the crawl and the main floor. It also is closed now b/c when I run the kitchen fan, the air from the crawl space comes up.

Answered by Brett Michaels
Posted Sep 2, 2014 11:13 AM ET


Some questions for you... When was the foam installed? Did you smell the odor right away? Where you in the home during installation or any of your family members? Did the installer ventilate the area and or home during installation? What were the surface temperatures and the foam as it was being installed? Did the installer test the foam as it was being installed? Who's product was installed?


Here's a simple non-published test to help you pin down your odor problem without spending thousands $$$$$ trying to get an answer which no one will admit to. Take a piece of your spray foam off and place it in a sealed mason jar. Leave it sealed for 2 days in your home and then open the jar. In another sealed jar perform the same procedure and place it in the outdoor days heat (shaded of course) for 4 to 6 hours not to exceed 120 degrees F. What do you smell? (Mason canning jars are available at Wal-Mart)


If you can smell the chemicals it's time to call in your installer and an industrial hygienist to investigate the claim. Also note... high humidity is also known to exacerbate a "bad" spray foam installation leading to noxious chemical odor problems.

FYI.. testing the foam is not as simple as you think. Labs only work with lawyers and hygienist, not consumers for real world testing and only certain labs have the capacity to test the chemical emissions to match them up with a chemical manufacturers foam. There are to many "proprietary" chemicals the chemical giant does not want you to know about. (Trade Secrets)

Properly mixed and installed spray foam should not smell with or without an operating air exchanger. Air exchangers are designed to dilute chemical emissions, not erase your natural born senses which are there to alert you to a problem. I hope your right and it's not the foam emitting the odor. Just my opinion.. Please keep us posted.... :)

Answered by Richard Beyer
Posted Sep 2, 2014 11:42 AM ET


We are still having problems. The builder, the contractor who worked on the energy star rating of the building, and the foam contractor came out and we found that the ERV was definitely not working correctly. We are working on that. Still not installed.

The builder believes that having the ERV pull fresh air into the house directly, and then having it pull old air from the crawl is the way to go. he says that having the ERV pulling exhaust from the return can cause problems with the ERV since it has such small fans and the HVAC has a much larger fan.

Incidentally, the basement is sealed and conditioned.

We all felt that excess humidity and still air was the problem, so we thought it would be helpful to get a fan and vent the crawl for a few days. After a week, the small was better, but still there. You can smell it at the fan exhaust.

Also, the fan seems to cause other problems. First, all that air going out has to come from somewhere and since the crawl is sealed, my guess is that it is coming from the walls/attic/floor of the house. So after a week, it smelled like paint. ugh.

Thinking that fresh air was needed, I opened a window and let the air flow from the window, through a transfer vent between the main floor and the crawl. The paint smell went away, but the crawl smell came back! I thought the air would just get pulled through the vent, but it seems the to be "pushed" back into the house. Weird and problematic, because while the ERV fan is much smaller, this is the same design and if the crawl smells, my guess is that it will find it's way back into the house.

In general the foam looks good and when you stick your nose up to it it doesn't smell. I'm going to do the mason test and report back.

What other smells could cause a chemical odor like this? Could humid earth under the vapor barrier be the issue? I don't see any obvious wet areas, but who knows. It doesn't smell like gas, or sewer, or dead animal. Definitely a chemical smell.

Answered by Brett Michaels
Posted Sep 11, 2014 9:56 PM ET


Brett Michaels,

In my opinion, Do the mason jar test and report back. If it does not release odor after baking in the afternoon sun 70+ degrees for a couple of days or even baking in the oven (with the lid sealed tight) no greater than 140F for 30 minutes then it's time to be concerned about something else. (Most ovens will not light below 140F) Foam breaks down @ 240F and begins to combust @ 350-450F.

If it stinks, you found your source. This temperature will resemble a non-conditioned attic temperature during the afternoon hours on a mildly hot day.

If your plastic ground barrier is sealed tightly then the soil odor below will not permeate the barrier. FYI... An air exchanger is not a fix all for a problematic SPFI installation. An air exchanger also has it's own port for the fresh air return and exhaust. Usually 4 ports.

See description.... http://www.venmar.ca/39-air-exchangers-e15-ecm-hrv-new.html#!prettyPhoto

What you described sounds more like a cheap exhaust fan with no return port, only exhaust.

Did the spray foam contractor install an intumescent paint over the spray foam for fire protection?

Answered by Richard Beyer
Posted Sep 11, 2014 11:26 PM ET


As my article on conditioned crawl spaces notes, you need some air exchange in your crawl space to meet code requirements. In the case of a house with a smelly crawl space, that means that you need a properly sized fan exhausting continuously from the crawl space, along with a grille that provides makeup air to the crawl space from the conditioned area above. All of this is explained in Building an Unvented Crawl Space.

Your ERV should not pull exhaust air from your crawl space. ERVs allow water vapor and other volatile chemicals to transfer from the exhaust air stream to the fresh air stream, so that plan is terrible. Instead, an ERV should be ducted to pull exhaust air from bathrooms, the laundry room, and in some cases the kitchen ceiling (but not near the stove).

Answered by Martin Holladay, GBA Advisor
Posted Sep 12, 2014 7:28 AM ET
Edited Sep 12, 2014 7:30 AM ET.

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