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  1. #1
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    Jan 2017
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    Crawlspace Makes My House Stink

    My crawlspace is making my house stink, but here's the thing: It only happens on rainy days.

    The smell in my house on rainy days is the same as the smell inside my crawlspace all of the time. If it's not raining, I don't smell it in my house. If it does rain – even just a little bit – I smell it in a big way.

    Some facts about my crawlspace and my house:

    1. HVAC is down there
    2. It's partially encapsulated, not fully
    3. I've got a vapor barrier all along the floor and nailed to the concrete walls about 6" above the ground.
    4. The vapor barrier also extends up the piers about 6".
    5. I've closed off/sealed all the vents.
    6. I've got a dehumidifier down there and keep it at 60% RH
    7. It's got relatively modest amounts of mold on the joists – nothing crazy. Just some fuzzy stuff. No more is growing b/c I've had the dehumidifier running down there for over a year. I've not cleaned the mold.
    8. I've sealed my ducts with mastic and mastic tape (Hardcast 1402) all over the place; I've even taped the air handler cabinet.
    9. I've sealed all the floor penetrations (HVAC, plumbing, electrical) with fire caulk.
    10. I have a whole-house dehumidifier that keeps the inside of my home at 50% RH or less.
    11. The dehumidifier has a ventilation damper that brings fresh air into my home, filtered and dehumidified, for 15 minutes out of every hour.

    So I've got this fancy crawlspace and fancy dehumidification/ventilation system and I still have an indoor air quality problem. It's been at 60% RH or less down there for over a year. I have no idea what to do, but...

    1. I've read reports about people smelling soil gas (not radon, but other gases) following crawlspace encapsulation. After installing the type of mitigation system normally used for radon, the smell went away.
    2. There is a particular type of vapor barrier that has, in some homes, given off a bad smell. I might have that type of vapor barrier, but I don't understand why I'd smell it considering I've sealed off my ducts and sealed the floor penetrations in the crawlspace.

    And the fact that I only smell it when it rains is just... weird. Any ideas? If it's soil gases, I'm wondering if I should seal the vapor barrier to the walls of the crawlspace before installing a radon mitigation system. Is that the next step? I'm at a loss.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    I am impressed with what you have done. You have a wet spot some place and a dam good nose.
    Because of dormant mold, I would lower the crawlspace to 50%RH and measure the amount of fresh air to assure a fresh air change in 4-5 hours, 24/7. 80-100 cfm 24/7. Most fresh air ducts do not bring in adequate fresh air. In most cases the fresh air duct needs to be enlarged. You will never stop crawlspace air from moving up into the home.
    After significant rain around a home, soil gas may be forced up into your crawlspace.
    Also the idea of a small amount of air sucked out from under the vapor barrier is great. Take a 4" radon fan sucking from the center of the space under the vapor barrier and exhaust to the outside. Tape or cauk the seams.Operate fan 24/7 during the times of the year when odors are sensed.
    You are real close.
    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

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  4. #3
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    Jan 2017
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    Thread Starter
    Quote Originally Posted by teddy bear View Post
    I am impressed with what you have done. You have a wet spot some place and a dam good nose.
    Because of dormant mold, I would lower the crawlspace to 50%RH and measure the amount of fresh air to assure a fresh air change in 4-5 hours, 24/7. 80-100 cfm 24/7. Most fresh air ducts do not bring in adequate fresh air. In most cases the fresh air duct needs to be enlarged. You will never stop crawlspace air from moving up into the home.
    After significant rain around a home, soil gas may be forced up into your crawlspace.
    Also the idea of a small amount of air sucked out from under the vapor barrier is great. Take a 4" radon fan sucking from the center of the space under the vapor barrier and exhaust to the outside. Tape or cauk the seams.Operate fan 24/7 during the times of the year when odors are sensed.
    You are real close.
    Keep us posted.
    Regards Teddy Bear
    Thanks, Teddy Bear.

    Can you clarify your comment: "assure a fresh air change in 4-5 hours, 24/7. 80-100 cfm 24/7."

    Are you just saying that the fresh air setting should be at whatever it needs to be to completely change out the air in my home every 4-5 hours? By 24/7 do you just mean it should be set up at all times of day to enable a complete air exchange every 4-5 hours?

    Also: Lowering the dehumidifier setting in the crawlspace to 50%... what will this do to the dormant mold? The crawlspace has already gone through an entire winter where the RH was around 30% down there. I figured the mold couldn't grow back as long as I set it to 60%. Could I be smelling dormant mold? Does that make sense?

    Do you think sealing the vapor barrier to the walls with some kind of caulk or mastic might keep the soil gases down there (if it is, in fact, soil gas that I'm smelling)? At present, the vapor barrier is tacked/nailed to the foundation wall, but not sealed.

  5. #4
    Join Date
    Jun 2017
    Location
    Atlanta, GA
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    I've got this same issue! I noticed that I had some water collecting near my air handler and decided it was time to replace (I assumed that was the culprit) I replaced with a Goodman Air Handler (got an INSANELY good deal and the house / AC was old so figured may as well) Anyway - here I am 2 months later; still dealing with the smell on rainy days. I too have a vapor barrier but I DON'T have a de-humidifier running down there. I guess my question is - do you think adding a de-humidifier would help me issue? I did NOT seal off my crawl space vents. Should I? Sorry - I know that's a lot. But I wanted to piggy back into this if I could because it's driving my wife (and me cause she's complaining to me) nuts!! Thanks

  6. #5
    Join Date
    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by greenink View Post
    Thanks, Teddy Bear.

    Can you clarify your comment: "assure a fresh air change in 4-5 hours, 24/7. 80-100 cfm 24/7."

    Are you just saying that the fresh air setting should be at whatever it needs to be to completely change out the air in my home every 4-5 hours? By 24/7 do you just mean it should be set up at all times of day to enable a complete air exchange every 4-5 hours?

    Also: Lowering the dehumidifier setting in the crawlspace to 50%... what will this do to the dormant mold? The crawlspace has already gone through an entire winter where the RH was around 30% down there. I figured the mold couldn't grow back as long as I set it to 60%. Could I be smelling dormant mold? Does that make sense?

    Do you think sealing the vapor barrier to the walls with some kind of caulk or mastic might keep the soil gases down there (if it is, in fact, soil gas that I'm smelling)? At present, the vapor barrier is tacked/nailed to the foundation wall, but not sealed.
    60%RH setting is on the edge for controlling odors from established mold. Dehumidistats may be inaccurate and have a dead band, on/off differential. Also sensing at the dehumidifier may be allow higher %RH in the far corners. Sealing alone will not be perfect. Soil gas pressure from change in moisture levels surrounding the home slowly migrate to the space. Either air change in the space or negative pressure below the vapor barrier should fix this. Pressurizing the home with 80-100 cfm of fresh air will stop/slow unfiltered air from entering your home from all sources. When windy, you get much more fresh air into your home. Operating your exhaust devices, like clothes drier, kitchen hood, and bath fans sucks in ail form all over.

    Yes, completely change out the air in 4-5 hours. This is a trickle but assures purging of pollutants and odors. This suggested by most experts. It is not very costly. Try it and see for yourself.
    You are close, just use the equipment you have more aggressively.
    Keep us posted.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by NoviceHVACguy View Post
    I've got this same issue! I noticed that I had some water collecting near my air handler and decided it was time to replace (I assumed that was the culprit) I replaced with a Goodman Air Handler (got an INSANELY good deal and the house / AC was old so figured may as well) Anyway - here I am 2 months later; still dealing with the smell on rainy days. I too have a vapor barrier but I DON'T have a de-humidifier running down there. I guess my question is - do you think adding a de-humidifier would help me issue? I did NOT seal off my crawl space vents. Should I? Sorry - I know that's a lot. But I wanted to piggy back into this if I could because it's driving my wife (and me cause she's complaining to me) nuts!! Thanks
    What is your wife complaining about? Vented crawlspaces will be damp when the wind is up, the outside dew point is high, and the a/c does not have high sensible cooling loads. Close the vents for lower indoor %RH, monitor the %RH until you are assured that the a/c alone does not keep the space 50%RH. Get a small whole house dehumidifier like the Ultra-Aire 70H. A 6" fresh air inlet connected to the dehumidifier is ideal.
    Get %RH meter from Walmart or where ever.
    Keep us posted on what you learn.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  8. #7
    Join Date
    Jun 2017
    Location
    Atlanta, GA
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    Quote Originally Posted by teddy bear View Post
    What is your wife complaining about?
    Better question may be "what DOESN'T she complain about?!" =P may sound stupid but I don't have a humidity monitor down there. Looks like I'm headed to Wal-Mart to scoop up the one that you recommended. Will most likely get down there again next weekend so I'll keep you posted once I have some data recorded on the %RH.

    Thanks again

  9. #8
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    Oct 2008
    Location
    Royal Palm Beach, FL
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    IMO, if you pressurize the crawl space air, you have to use outside air to provide the air to pressurize the crawl space. Outside Air with Humidity. Thereby making the problem worse. Just normal air exfiltration will make the crawl space humidity higher always. Its not easy to fool your Mother Nature.

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