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  1. #1
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    Crawl space dehumidifier without vapor barrier?

    I have a very humid crawl space which causes my house to be overly humid (70+%). Water used to get into my crawl space due to poor yard drainage. I've fixed that but the crawl space is still very humid. I plan on sealing the crawl space vents and I'm wondering if I can add a crawl space dehumidifier without adding a vapor barrier? My crawl space has a dirt floor and is about 24" tall. I wasn't sure if a vapor barrier is required in order to successfully use a dehumidifier. If a vapor barrier is a must, is it worth it to look into the huge expense of full encapsulation or would a simple vapor barrier likely be good enough when combined with a good dehumidifier? Thanks in advance for any advice.

  2. #2
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    Just the dehumidifier will remove moisture from the crawlspace air. But as the majority of the moisture comes from the dirt floor - covering it with a vapor barrier will make the dehumidifying process much more efficient and effective.

    How is the ground graded around your house? Does it pitch away or toward the house?

    PHM
    ----------------



    Quote Originally Posted by brock125 View Post
    I have a very humid crawl space which causes my house to be overly humid (70+%). Water used to get into my crawl space due to poor yard drainage. I've fixed that but the crawl space is still very humid. I plan on sealing the crawl space vents and I'm wondering if I can add a crawl space dehumidifier without adding a vapor barrier? My crawl space has a dirt floor and is about 24" tall. I wasn't sure if a vapor barrier is required in order to successfully use a dehumidifier. If a vapor barrier is a must, is it worth it to look into the huge expense of full encapsulation or would a simple vapor barrier likely be good enough when combined with a good dehumidifier? Thanks in advance for any advice.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #3
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by Poodle Head Mikey View Post
    Just the dehumidifier will remove moisture from the crawlspace air. But as the majority of the moisture comes from the dirt floor - covering it with a vapor barrier will make the dehumidifying process much more efficient and effective.

    How is the ground graded around your house? Does it pitch away or toward the house?

    PHM
    ----------------
    Could not have said it better myself.
    Normal ground wicks water from any ground water source from below down to 1,000 ft. Cove the earth with 10 mil plastic covering all the exposed earth with gravel or spicks eliminating air circulation under the plastic.
    Keep us posted on the results.
    The Santa Fe Compact or Ultra-Aire 70H are good minimal dehumidifiers. They good fro upto 3,000 sqft. Close the Vents.
    Make sure you a/c is set up to maintain 50%RH during peak cooling colds and high outdoor dew points.
    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"

  4. #4
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    Thread Starter
    Quote Originally Posted by Poodle Head Mikey View Post
    Just the dehumidifier will remove moisture from the crawlspace air. But as the majority of the moisture comes from the dirt floor - covering it with a vapor barrier will make the dehumidifying process much more efficient and effective.

    How is the ground graded around your house? Does it pitch away or toward the house?

    PHM
    ----------------
    The ground around my house varies. There is one low point where the water can gather at the base of my house. I used to have an issue where a downspout moved the water out about 6 ft but it would end up draining back to the low point. I dug a trench and put in a 70 ft drain pipe so now the downspout goes directly into that pipe. I also added a catch basin about 8 ft from my house at the edge of the low spot. We've had a couple of decent showers here in Dallas over the past month and I haven't seen any standing water around my house or in the crawl space like I used to see in both places. I know I still need to change the grade of the slope to make sure that it slopes away from my foundation in all spots. That's on my To Do list.

    Is there a best way to seal crawl space vents? I have 5 of them and have added metal covers (not sealed all that well) around 4 of them. The 1 remaining uncovered one has the central air coolant line and condensation line running through it. Is that normal or should they be rerouted through the side of the wall of the crawl space? I've owned the house for about 18 months now so most of this stuff is new to me (1st house).

    The crawl space has a dirt floor and it looks very "wavy", if that's a term. I can't see pencil-sized roots at spots near the surface edge. There is a bit of debris in there too from when the previous owners remodeled the house prior to me purchasing it. How would the waviness and debris affect the vapor barrier? I assume it would be best to removed the debris first. My only access to the crawl space is about a 24" cutout in one of my closets.

    I also looked at the dehumidifiers that were suggested. My crawl space is about 1200 sq ft and around 24" tall. Is it best to hand the dehumidifiers from the floor joists? Should they be situated in any certain way so they can move the air in the most efficient way?

    I really appreciate the responses I've already received. You guys are great for helping us inexperienced people out. Thank you so much!

  5. #5
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    Hanging the unit would be best as it would be away from the humid and dirty floor and easier to service. Put the unit(s) as close to the access panel as possible. The humidity will always equalize throughout the space so placement-for-effectiveness is not a factor. Make it easy to get to - someone will eventually appreciate your thoughtfulness. And it may even be you. <g>

    I think I would use a long handled gravel rake to both remove debris and to even the dirt floor level at the same time. Wear coveralls and wear a good respirator filter mask. Direct a fan to supply fresh air down into the crawlspace while you work.

    All of the ground immediately around the house foundation should be higher than the ground is 6-8-12 feet away from the foundation walls. You can't see the water under the ground - and you don't want it flowing towards the house.

    Roots in the crawlspace are bad. They went in there seeking water and they had to grow through the wall structure to get there.

    PHM
    ------------






    Quote Originally Posted by brock125 View Post
    The ground around my house varies. There is one low point where the water can gather at the base of my house. I used to have an issue where a downspout moved the water out about 6 ft but it would end up draining back to the low point. I dug a trench and put in a 70 ft drain pipe so now the downspout goes directly into that pipe. I also added a catch basin about 8 ft from my house at the edge of the low spot. We've had a couple of decent showers here in Dallas over the past month and I haven't seen any standing water around my house or in the crawl space like I used to see in both places. I know I still need to change the grade of the slope to make sure that it slopes away from my foundation in all spots. That's on my To Do list.

    Is there a best way to seal crawl space vents? I have 5 of them and have added metal covers (not sealed all that well) around 4 of them. The 1 remaining uncovered one has the central air coolant line and condensation line running through it. Is that normal or should they be rerouted through the side of the wall of the crawl space? I've owned the house for about 18 months now so most of this stuff is new to me (1st house).

    The crawl space has a dirt floor and it looks very "wavy", if that's a term. I can't see pencil-sized roots at spots near the surface edge. There is a bit of debris in there too from when the previous owners remodeled the house prior to me purchasing it. How would the waviness and debris affect the vapor barrier? I assume it would be best to removed the debris first. My only access to the crawl space is about a 24" cutout in one of my closets.

    I also looked at the dehumidifiers that were suggested. My crawl space is about 1200 sq ft and around 24" tall. Is it best to hand the dehumidifiers from the floor joists? Should they be situated in any certain way so they can move the air in the most efficient way?

    I really appreciate the responses I've already received. You guys are great for helping us inexperienced people out. Thank you so much!
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #6
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    Feb 2019
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    Thread Starter
    Thanks again for the responses. Any ideas on my question below about sealing the vents? What do people usually use to seal them? Foam board?

    Is there a best way to seal crawl space vents? I have 5 of them and have added metal covers (not sealed all that well) around 4 of them. The 1 remaining uncovered one has the central air coolant line and condensation line running through it. Is that normal or should they be rerouted through the side of the wall of the crawl space? I've owned the house for about 18 months now so most of this stuff is new to me (1st house).

  7. #7
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    Jun 2003
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    Madison, WI/Cape Coral, FL
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    Stop air movement in a light breeze. Caulk or foam will do the job.
    Here is the other side of the coin. Your home need a fresh air change in 4-5 hours when occupied and calm winds to purge indoor pollutants. This is needed purge indoor pollutants and renew oxygen during calm winds and occupancy.
    In my house, I wold use a small whole house dehumidifier in the crawlspace with the fresh air option connected to the a/c and a small dry air supply to the crawlspace.
    This will get the needed fresh air to the home and humidity control to entire home.
    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"

  8. #8
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    Thread Starter
    Quote Originally Posted by teddy bear View Post
    Stop air movement in a light breeze. Caulk or foam will do the job.
    Here is the other side of the coin. Your home need a fresh air change in 4-5 hours when occupied and calm winds to purge indoor pollutants. This is needed purge indoor pollutants and renew oxygen during calm winds and occupancy.
    In my house, I wold use a small whole house dehumidifier in the crawlspace with the fresh air option connected to the a/c and a small dry air supply to the crawlspace.
    This will get the needed fresh air to the home and humidity control to entire home.
    Keep us posted.
    Regards Teddy Bear
    Can you explain the fresh air change to me?

  9. #9
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    Jun 2003
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    Quote Originally Posted by brock125 View Post
    Can you explain the fresh air change to me?
    You start by building a home that does not leak air excessively in a strong wind or extreme cold.
    When that is done as best as reasonably do able, you find that in mild calm air, the home does not get enough air to purge indoor pollutants and renew oxygen.
    It take a fresh filtered air change in 4-5 hours purge indoor pollutants and renew oxygen typically.
    Makes sense to have a small mechanical device that introduces that amount of filtered air, mixes it with house air, circulates the fresh filtered air through the home, when the home is occupied. In green grass climates, moisture should be maintained <55%RH to avoid mold/dust mites and be comfortable.
    A simple method of providing this is a small whole house dehumidifier with fresh air option like the Ultra-Aire.
    Ultra-Aire.com
    You also need a well setup a/c to do the heavy dehumidification during peak sensible cooling loads. The dehumidifier is sized for evenings, rainy days, plus the moisture from the occupants.
    Simple!
    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"

  10. #10
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    Apr 2003
    Location
    St. Louis
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    What have you done with the joists and subfloor. High RH goes to low RH so if the RH is higher in the house it will migrate down or up. After closing my crawl space vents off spraying insulating foam on the back side, taking all ductwork out adding dehumidifier found all waters lines sweating had to insulate both hot and cold lines. Using mini splits for a system.

  11. #11
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    Feb 2019
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    Thread Starter
    I have a question about installing the vapor barrier. I have a pier and beam foundation. Do I also cover the beams with plastic? What about the walls? I wasn’t sure if installing a vapor barrier was the same as the similar step in the encapsulation process.

    Is installing a vapor barrier something that an average “handyman” could do? I’d normally try to do it myself but I have a short crawl space and I’m a big guy. I’m looking to see if one of the neighborhood handymen can do it. I’m planning on buying some of the heavier duty plastic gurvghe vapor barrier. Do I need to add any padding or anything on top of the dirt prior to covering it with the plastic? I plan on clearing out the debris that is currently scattered throughout my crawl space first. Any other tips/suggestions would be greatly appreciated. Thanks!

  12. #12
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    Quote Originally Posted by servicefitter View Post
    What have you done with the joists and subfloor. High RH goes to low RH so if the RH is higher in the house it will migrate down or up. After closing my crawl space vents off spraying insulating foam on the back side, taking all ductwork out adding dehumidifier found all waters lines sweating had to insulate both hot and cold lines. Using mini splits for a system.
    Cover all earth plastic and close off outside air. Add a dehumidifier that is capable of lowering the interior dew point below the temperature of cold surfaces.
    Condensation can not occur.
    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"

  13. #13
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    Thread Starter
    Quote Originally Posted by teddy bear View Post
    Cover all earth plastic and close off outside air. Add a dehumidifier that is capable of lowering the interior dew point below the temperature of cold surfaces.
    Condensation can not occur.
    Keep us posted.
    Regards Teddy Bear
    Do I need to run the plastic up the foundation piers or the walls at all?

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