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Community and Q&A

Source of ammonia odor in a home (indoor air quality)

Andrew Katz | Posted in Green Products and Materials on

We have built a home which is well air sealed and have registered for LEED status, which will be finalized later, when the alternative energy projects and landscaping are complete.

We have built a root cellar off of our basement. It is outside our thermal envelope and has a dirt floor covered with pea gravel and topped with concrete patio pavers from our local home improvement store. It currently is not ventilated, but will be as soon as our excavator and builder put in the 4″ PVC fresh air intake/exhaust pipes. The walls are of ICF overlaid with moisture resistant drywall and covered with commercial grade textured panels such as found on bathroom walls.

Once the exterior door between the basement and the cellar was put in place and closed, the root cellar began to accumulate the odor of ammonia. We did have the door in place before the pavers were laid and no odor was previously detected, therefore I assume it is not coming from the soil or gravel but the pavers themselves. I know that some concrete mixes can be contaminated with ammonium compounds and I assume this is the source of my outgassing. Is there a way to treat the floor to eliminate the outgassing? I don’t want to harm the floor or use a toxic compound. I have considered dilute hydrochloric acid or acetic acid (white vinegar). Has anyone had this type of experience? Any ideas? Do I need to change out the flooring? There is no odor anywhere else in the home.

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  1. Steve Knapp CZ 3A Georgia | | #1

    Andrew. Where are you located? What type of soil conditions do you have?

    I know nothing about root cellars, but the Google suggests people often build them as inexpensive and sometimes temporary structures. I get the feeling you want to create some more enduring, correct?

    I noticed in many of the online plans the root cellar has a simple dirt floor or possible a gravel floor. In wet areas, owners seem to install sump pumps.

    I am curious about your material choices and some of your build details. Did you follow a proven design to create the root cellar, or is the design something you conceived on your own?

    I read online that root cellars are supposed to be humid, but I suspect that is the underlying cause of your odor problem. You indicate your walls include a drywall layer. Which type exactly (green board)?

    Did you install polyethylene over the gravel layer or a four-inch perforated pipe in the gravel layer to help control and vent moisture?

  2. GBA Editor
    Martin Holladay | | #2

    Since more and more building products sold in the U.S. are manufactured in China, anything is possible. Of course, U.S.-made building products sometimes have funny smells, too.

    It's possible that the moisture-resistant drywall, or the textured wall panels, or the pavers are emitting a funny smell. It's also possible that the damp conditions in your cellar are exacerbating the smell.

    You have two choices:

    (a) Wait until the ventilation ducts are installed to see whether ventilation reduces the smell to an acceptable level.

    (b) Remove building materials, one layer at a time, until you find the culprit.

    I think that pavers are unnecessary in a root cellar. Crushed stone makes an acceptable floor, as long as you don't anticipate visiting your root cellar with bare feet. (If you are a bare-feet kind of person, you could get rounded decorative pebbles instead of crushed stone.)

    Since manufacturers of pavers assume that their products will only be used outdoors, I can easily imagine that the manufacturers don't consider indoor air quality issues when manufacturing their products.

  3. Steve Knapp CZ 3A Georgia | | #3

    I found a blog detailing one owner's process for building a wet and dry root cellar. Very impressive effort:

  4. Andrew Katz | | #4

    The Root Cellar is based on a fairly extensive treatise of Root Cellars. Root Cellaring" by Mike and Nancy Bubel.

    The odor is definitely ammonia as my chemist nose and very sensitive sense of smell identify it.

    The soils here if Northeast Indiana are clay and somewhat alkaline. The cellar has an underlying dirt floor with a layer of gravel over it. The pavers were laid on top to create a more aesthetically pleasing and level surface on which to place shelving. It is inappropriate to place a moisture barrier on the floor. Our walls are ICF and the ceiling is foam insulated under a steel material with a reinforced concrete porch above. The cellar floor has, by design, a high moisture content as relative humidity in a root cellar should be high. We are aiming for an average relative humidity of 80% and a temperature of 50-55 degrees F. This is an experiment for all of us.

    As you suggest, I will add the Air Intake/Exhause piping and observe. FYI, the 4" PVC Intake enters near the floor and the exhaust is near the ceiling to use convection to move air through this approx 10x15' space.

  5. Expert Member
    Malcolm Taylor | | #5

    It is a hard one to diagnose, especially from a distance. I've never heard of concrete smelling of formaldehyde, but there are lots of accounts of both foam and drywall giving off that odor.

  6. Steve Knapp CZ 3A Georgia | | #6

    Hi Andrew. Most visitors to this site are attempting to build or remodel residential structures to make them more efficient and comfortable. So it may not be the best place to seek advice on this particular topic.

    Maybe the ammonia smell is simply soil gas, and it will dissipate if you increase the root cellar's ventilation rate. (I recognize that you don't want too much ventilation since you are trying to maintain a high humidity level.)

    But as I mentioned in post 1, I am curious about the drywall you used in your wall assembly. Greenboard isn't waterproof, for example, and would probably start breaking down if used in a wet root cellar. Fiberglass encapsulated gypsum handles moisture better--if all penetrations and exposed edges are properly sealed.

  7. Mel Tillyard | | #7


  8. Expert Member
    Dana Dorsett | | #8

    So, the root cellar is insulated but has no ground vapor retarder(?). Is there a reason why it's only pea-gravel with pavers, no vapor retarder?

    A root cellar ventilated with outdoor air will be plenty humid just from the ventilation air during the summer- you don't really need or want ground moisture in there, and may even need to limit the amount of summertime ventilation to keep it from being too damp. The target conditions of 80% RH @ 55F, has a dew point of 49F, which is well below the average outdoor air dew point in summer.

  9. Steve Knapp CZ 3A Georgia | | #9

    Dana. I didn't get it either, but wet root cellars apparently are supposed to be cool and very moist (like 90%) to extend the shelf life of various root vegetables. Dirt floors with a gravel layer is what most people put down. Personally, I would have reservations about such a room to my main living space, even via an airlock in the basement. But I'm not homesteading or trying to live off the land.

  10. GBA Editor
    Martin Holladay | | #10

    I agree with Andrew: traditional root cellars shouldn't have polyethylene over the dirt floor.

    Whether a modern home should include a root cellar is controversial. My house is about 36 years old, and the entire cellar is a dirt-floored root cellar without any polyethylene. The floor joists above the roof cellar are still sound.

    I'm not saying that I recommend this approach -- proceed at your own risk. But my house is sound, and my carrots, potatoes, beets, and cabbages last all winter long.

  11. Expert Member
    Dana Dorsett | | #11

    Ventilating with outdoor air in winter would lower the RH in the root cellar, for the same reasons that venting it in summer raises the RH. If the wintertime RH needs to be 80-90% to keep the goods from dessicating, the moisture would indeed have to come either from the ground, or the stored roots themselves, with the wintertime ventilation dialed back.

  12. GBA Editor
    Martin Holladay | | #12

    The standard advice is to ventilate in October, to bring the temperature of the cellar to the 30s. By the end of October, ventilation openings are sealed for the winter.

    Of course, this advice may need to be modified depending on outdoor temperatures in your climate zone.

  13. Expert Member
    Michael Maines | | #13

    Mel didn't waste any words, but his suggestion that it might be cats is worth considering. On a few occasions, when I've inspected "stinky" crawlspaces or basements, animal urine or spray was the likely culprit. It could have been there a long time before you closed things up. You might try a product made to neutralize cat spray. Here's some more info:

  14. Drew Baden | | #14

    Could this be decomposing organic material? I had this same problem when I parked my grass-laden mower in my garage. I went back into the garage a few days later and it stunk exactly of ammonia. I also had my camper next to it, which contained an ammonia absorption refrigerator and I thought had a huge leak to the point where I started looking into the functionality of the refrigerator. I was pleased to learn that the ammonia smell was nothing more than decomposing clumps of grass on the deck mower.

  15. GBA Editor
    Martin Holladay | | #15

    Another possibility is a dead mouse. It's amazing how much of a stink such a small dead creature can produce.

  16. Expert Member
    Malcolm Taylor | | #16

    Or frog.

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