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High Moisture Level Crawl Space?
Old 06-07-2019, 04:51 PM   #1
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High Moisture Level Crawl Space?

We’re scheduled to close on a 3 yr old house in just over a week. The home inspection yesterday came back pretty clean with mostly small easily corrected issues. However there was one major issue (actual report below) and we’ve never had a house on a crawl space. Whatever the source(s) of the high moisture, it’s not something we want to just accept - high moisture can lead to mold, termites/wood boring insects, critters, air quality issues and sagging floors, cracked drywall or even structural issues eventually.

We’ve scheduled a foundation/crawl space expert firm (Dry-Pro) to do an assessment and $ estimate next Tuesday. Our due diligence period ends Thursday.

Any experience with an issue like this? I’m just trying to educate myself and get ahead of the situation.

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(1) The moisture level in the floor system is elevated in the crawlspace. Water intrusion signs were seen at one right side foundation vent, all front right foundation vents and at one left side foundation vent. Some of the vent wells have leaves and debris inside which could be allowing water to enter. The ground at the rear of the crawlspace was very damp and muddy. Moisture readings ranged from 18% to 22%. It has been 25 days with no rain in the area and it is unusual to see the dampness in the crawlspace. If not corrected, excessive moisture in the wood may lead to deterioration of building components which can increase repair costs. Here is some info about crawl space moisture levels from a local engineering company. Runoff water from the roof should be checked to ensure that all of it is adequately piped away from the foundation. A crawlspace drain was found at the left rear but no drain was seen at the right rear which is isolated from the left side. Three drain pipes were seen in the rear yard which may all be coming from the crawlspace since no downspouts have underground drains. If this is the case, the other two drains may be covered up and in need of clearing. I recommend a qualified contractor investigate further and perform any needed corrective actions. Monitoring the moisture levels over time is also recommended to ensure that the corrective actions are working and are adequate.
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Old 06-07-2019, 05:09 PM   #2
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The answer is usually very straightforward:
- Assure good ventilation (open and unblock the vents)
- cover the soil floor in the crawlspace with thick plastic. This needs to be done right--all the way to the foundation and up a bit, weighted down everywhere along the perimeter, no open seams, no open penetrations at the piers, pipes, etc. A nicer approach is to pour a concrete "rat slab" over the plastic to protect it.
- finding what is going on with those drains might be a struggle. You need to get the water away from the foundation. If there's a slope that leads water against the foundation, then it needs to be re-sloped or a curtain/foundation drain installed, and it is better for it to be outside the foundation than in the crawlspace.
- in some cases, it may be necessary to prevent intrusion of water vapor through the foundation walls. That can be done with the right kind of paint/coatings in some cases. Keeping liquid water out is best done from the outside
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Old 06-07-2019, 05:19 PM   #3
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I canít add anything to Samclemís answer, heís very knowledgeable in these matters. That sounds like a lot of moisture, though, and it wonít be a minor expense to remedy. Did the engineer give a cost estimate? If not, Iíd postpone the closing and get a couple of quotes from companies that specialize in foundation leak repairs.
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Old 06-07-2019, 05:33 PM   #4
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I also agree with samclem. Interestingly enough, when I bought a house in NC in 1994, the inspector also found the moisture level was just a little too high, though it hadn't caused any problems yet. Maybe a 10 year old house? He recommended the plastic sheeting, but said to not run it up the sides, but instead leave a few inches all the way around. But when I look now, every source seems to recommend running it up the side. I don't recall the theory my guy had. When I sold the house 7 years later, nothing was flagged on the inspection.

It could just be that the yard isn't graded well to move water away from the house. I hope a foundation expert looks at that as well as the foundation itself.

Definitely a big issue down there. If it's that moist in a dry spell, it's got to be worse after rains. The Carolina clay just doesn't absorb moisture like good Midwestern soil does, so if the water does have a place to run off, much of it just sits there.
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High Moisture Level Crawl Space?
Old 06-07-2019, 05:47 PM   #5
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High Moisture Level Crawl Space?

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Originally Posted by RunningBum View Post
I also agree with samclem. Interestingly enough, when I bought a house in NC in 1994, the inspector also found the moisture level was just a little too high, though it hadn't caused any problems yet. Maybe a 10 year old house? He recommended the plastic sheeting, but said to not run it up the sides, but instead leave a few inches all the way around. But when I look now, every source seems to recommend running it up the side. I don't recall the theory my guy had. When I sold the house 7 years later, nothing was flagged on the inspection.

It could just be that the yard isn't graded well to move water away from the house. I hope a foundation expert looks at that as well as the foundation itself.

Definitely a big issue down there. If it's that moist in a dry spell, it's got to be worse after rains. The Carolina clay just doesn't absorb moisture like good Midwestern soil does, so if the water does have a place to run off, much of it just sits there.

It is an issue down here. Lots of trees. Depending on the situation, a tree canopy close to the property can also prevent moisture from drying out (direct sun is blocked). Deep greens and blues.
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Old 06-07-2019, 06:07 PM   #6
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Originally Posted by MichaelB View Post
I canít add anything to Samclemís answer, heís very knowledgeable in these matters. That sounds like a lot of moisture, though, and it wonít be a minor expense to remedy. Did the engineer give a cost estimate? If not, Iíd postpone the closing and get a couple of quotes from companies that specialize in foundation leak repairs.
The inspection and estimate come Tuesday. Hopefully weíll have a better idea then.
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Old 06-07-2019, 06:09 PM   #7
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............ He recommended the plastic sheeting, but said to not run it up the sides, but instead leave a few inches all the way around. But when I look now, every source seems to recommend running it up the side. I don't recall the theory my guy had. .......
I believe an open strip is left at the top to be able to see termite tunnels extending from ground level to the wooden floor.

Agree with Samclem in general - once any water is eliminated, you want to use 6 mil plastic to seal off the ground and foundation below ground level. I found some standing water in mine after a heavy rain and it was just due to a downspout extension that was misplaced. Generally, just proper grading is enough to keep a crawlspace dry, though back fill tends to settle over time so there may be low spots or negative grade in some areas adjacent to the foundation.

YouTube has a lot of videos on crawlspaces.
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Old 06-07-2019, 06:11 PM   #8
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Originally Posted by RunningBum View Post
I also agree with samclem. Interestingly enough, when I bought a house in NC in 1994, the inspector also found the moisture level was just a little too high, though it hadn't caused any problems yet. Maybe a 10 year old house? He recommended the plastic sheeting, but said to not run it up the sides, but instead leave a few inches all the way around. But when I look now, every source seems to recommend running it up the side. I don't recall the theory my guy had. When I sold the house 7 years later, nothing was flagged on the inspection.

It could just be that the yard isn't graded well to move water away from the house. I hope a foundation expert looks at that as well as the foundation itself.

Definitely a big issue down there. If it's that moist in a dry spell, it's got to be worse after rains. The Carolina clay just doesn't absorb moisture like good Midwestern soil does, so if the water does have a place to run off, much of it just sits there.
There is plastic sheeting covering the floor of the crawl space, but I have no idea yet of the quality of the install.

Iíve seen several sites that suggest a dehumidifier is part of the solution, but others say thatís a band aid at best. It does seem counterintuitive to me that a dehumidifier would do much in a totally vented space.
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Old 06-07-2019, 06:24 PM   #9
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There is plastic sheeting covering the floor of the crawl space, but I have no idea yet of the quality of the install.

Iíve seen several sites that suggest a dehumidifier is part of the solution, but others say thatís a band aid at best. It does seem counter intuitive to me that a dehumidifier would do much in a totally vented space.
There are two schools of thought on crawlspaces. One is the long used, vents open in summer, closed in winter and the second is no vents, careful sealing and either a connection to the main floor HeVac ducting (conditioned space) or a separate dehumidifier.

I've seen studies that show that venting doesn't work all that well because the ground is cooler than the air in summer. Outside, moist air getting into the crawlspace tends to condense when it comes into contact with the cooler ground.
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Old 06-07-2019, 07:08 PM   #10
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There is plastic sheeting covering the floor of the crawl space, but I have no idea yet of the quality of the install.

Iíve seen several sites that suggest a dehumidifier is part of the solution, but others say thatís a band aid at best. It does seem counterintuitive to me that a dehumidifier would do much in a totally vented space.
A humidifier is very unlikely to keep up, and it would jack up your energy bills. Seems like a last grasp if nothing else works, and not a plan for a house you're looking to buy.
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Old 06-07-2019, 07:20 PM   #11
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There are two schools of thought on crawlspaces. One is the long used, vents open in summer, closed in winter and the second is no vents, careful sealing and either a connection to the main floor HeVac ducting (conditioned space) or a separate dehumidifier.

Yes to the above. The later approach basically treats the crawlspace like another room in the house (with supply and return ductwork from the HVAC system), and it works very well. It is the surest way to protect wooden structural members in the crawlspace, and provides warmer floors in the winter. But, it still requires that the dirt floor be covered well with a vapor barrier and, for energy efficiency purposes, the walls of the crawlspace need to be insulated (since you'll be pumping warm air down there in the winter, cool air in the summer). Insulating the foundation walls and header bays can be done quickly and easily by a pro with spray foam (though the material is pricey). If access is okay and you want to DIY, rigid sheet foam works well and the edges can be sealed with Great Stuff.
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Old 06-07-2019, 08:47 PM   #12
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We have a lot of experience with this situation. A sealed crawlspace is ideal. Go to crawlspaces.org for more information. Building code allows several ways to control the humidity in a sealed crawl. Your contractor should choose the code approved solution that is site specific for your house. In the southeast a vented crawl is the worst for mold and rot.
P.S. no need to buy a dehumidifier marketed just for crawls. They are overpriced. Any dehu will work in a sealed crawl as long as itís rating meets code- normally 15 pints per day min. Your contractor can pipe the condensate from the dehu outside so youíll never have to literally crawl under there and empty a bucket. We also recommend installing a remote humidity sensor that will give you a reading in the crawl space so you can monitor the humidity which should be below 50% to prevent mold growth. Of course, all perimeter drainage must be installed correctly and slopes properly before you seal the crawlspace.
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Old 06-08-2019, 01:48 AM   #13
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Yes to the above. The later approach basically treats the crawlspace like another room in the house (with supply and return ductwork from the HVAC system), and it works very well. It is the surest way to protect wooden structural members in the crawlspace, and provides warmer floors in the winter. But, it still requires that the dirt floor be covered well with a vapor barrier and, for energy efficiency purposes, the walls of the crawlspace need to be insulated (since you'll be pumping warm air down there in the winter, cool air in the summer). Insulating the foundation walls and header bays can be done quickly and easily by a pro with spray foam (though the material is pricey). If access is okay and you want to DIY, rigid sheet foam works well and the edges can be sealed with Great Stuff.
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We have a lot of experience with this situation. A sealed crawlspace is ideal. Go to crawlspaces.org for more information. Building code allows several ways to control the humidity in a sealed crawl. Your contractor should choose the code approved solution that is site specific for your house. In the southeast a vented crawl is the worst for mold and rot.
P.S. no need to buy a dehumidifier marketed just for crawls. They are overpriced. Any dehu will work in a sealed crawl as long as it’s rating meets code- normally 15 pints per day min. Your contractor can pipe the condensate from the dehu outside so you’ll never have to literally crawl under there and empty a bucket. We also recommend installing a remote humidity sensor that will give you a reading in the crawl space so you can monitor the humidity which should be below 50% to prevent mold growth. Of course, all perimeter drainage must be installed correctly and slopes properly before you seal the crawlspace.
What I think I’ve learned:
  • Sealing the crawl space floor better isn’t going to mitigate high moisture and neither is clearing vents and drains because relative humidity is too high for much of summer. Ideally the crawl space will be around 50% RH or less, anything above 60-70% RH brings problems with mold, termites, etc. Moisture will be condensing out constantly during summer and parts of spring and fall.
  • Putting in a humidifier in a vented crawl space is a waste of money that won’t help. If a contractor suggests it I’m probably going to be suspicious, I’ve seen such recommendations online and that just doesn’t make any sense to me in a vented crawl.
My Dad used to say “a little information is dangerous,” but I’ve been reading and watching videos for hours and I’m starting to conclude crawl space encapsulation may be the only solution I can live with - this is a forever home we’re buying. That includes perimeter drains, sealing off all existing vents, a new better access door, insulating the crawl space walls, a thick vapor barrier with seam sealing over the entire floor and up all the walls and pillars, termite barrier at sill-foundation, a dehumidifier that drains condensate outside and maybe a sump pump or better drainage. Not sure about floor insulation between joists, don’t know what’s there or what’s appropriate. At least the inspector said there’s no mold or termite damage in the crawl space yet (house less than 3 years old).

From what I can tell encapsulation could easily cost $10-15K (2600 sqft footprint) but the crawl space professionals will provide a cost I can share with the sellers. Our signed offer was for top dollar/almost asking so I’m probably going to ask the sellers for a full amount price reduction for the crawl space encapsulation- and unfortunately I suspect that will kill the deal. It appears the sellers know less than squat about houses (even the simplest questions we’ve asked have been answered with “we don’t know anything about that”) so I suspect they’ll assume I’m being unreasonable without bothering to understand the crawl space issue. Too bad as we really like the house otherwise...
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Old 06-08-2019, 05:41 AM   #14
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............ It appears the sellers know less than squat about houses (even the simplest questions weíve asked have been answered with ďwe donít know anything about thatĒ) so I suspect theyíll assume Iím being unreasonable without bothering to understand the crawl space issue. Too bad as we really like the house otherwise...
My emphasis above....that seems to be the standard answer these days of "full disclosure" in real estate transactions.

Good luck, and if this deal falls apart, there are many other houses for sale.
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Old 06-08-2019, 08:04 AM   #15
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My Dad used to say ďa little information is dangerous,Ē but Iíve been reading and watching videos for hours and Iím starting to conclude crawl space encapsulation may be the only solution I can live with - this is a forever home weíre buying. That includes perimeter drains, sealing off all existing vents, a new better access door, insulating the crawl space walls, a thick vapor barrier with seam sealing over the entire floor and up all the walls and pillars, termite barrier at sill-foundation, a dehumidifier that drains condensate outside and maybe a sump pump or better drainage. Not sure about floor insulation between joists, donít know whatís there or whatís appropriate.
If you decide to go this route, then you can either choose to:
1) Incorporate the crawlspace into the conditioned envelop of the home (just like another room--heat it and cool it). The heating and cooling of this space won't change your utility bill much at all, since the walls of the crawlspace will be insulated.
2) Just run a dehumidifier in the crawlspace and don't incorporate it into the HVAC envelope. It would be hot in the summer, cold in the winter.


If you go with 1), you would not need insulation between your floor joists. Also, your existing HVAC system will be doing the dehumidification of the crawlspace, so you wouldn't need to add another mechanical "thing" (a dehumidifier, which will become a no-fail ite, to inspect and keep operational). If you go with 2 you'll need to keep the floor insulation between the joists.
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Old 06-08-2019, 08:33 AM   #16
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Just a quick comment... before deciding to seal a crawlspace and connect it with the house's HVAC system to make it conditioned space, BE SURE that the house is not in a radon area!
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Old 06-08-2019, 09:02 AM   #17
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Just a quick comment... before deciding to seal a crawlspace and connect it with the house's HVAC system to make it conditioned space, BE SURE that the house is not in a radon area!
Hopefully that was part of the inspection. We have a crawl space and when we purchased the house we had a radon test done. Radon came in at an 8, which is reasonably high. We had it mitigated by covering it with plastic and adding a fan out the side of the foundation. The radon dropped to 1.
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Old 06-08-2019, 10:19 AM   #18
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My crawl space had moisture had it encapsulated in plastic, it had the auto vents in it that closed in the cold, they removed them and insulated everything above grade. I run a dehumidifier and monitors to keep it under 60 %.
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Old 06-08-2019, 10:26 AM   #19
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ďwe donít know anything about thatĒ seems to be the standard answer these days of "full disclosure" in real estate transactions.
We sold my mom's house last year after she had a stroke. I hadn't seen her in over 20 years so I literally knew nothing about that house.

Midpack,

The best things you can do to control moisture in a crawlspace is to slope the yard away from the house, and make sure gutters and downspouts drain away from the house too.

Then make sure the entire crawlspace is covered with at least a 6mil thick plastic vapor barrier.

Most building codes require 1 square foot of vent for every 150 square foot of crawlspace. You can get by with less venting by installing the vapor barrier in the crawlspace. If you still have moisture issues, you can install powered ventilation fans such as this:

https://www.homedepot.com/p/110-CFM-...n-V1/302248029

https://www.amazon.com/Tjernlund-Und.../dp/B077SQJ65F

If you have standing water in the crawlspace, you may need to install drains and a sump pump, again discharging the water from from the house.
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Old 06-08-2019, 10:34 AM   #20
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Just a quick comment... before deciding to seal a crawlspace and connect it with the house's HVAC system to make it conditioned space, BE SURE that the house is not in a radon area!
It’s been tested for radon (0.4) and it’s not an issue for this house, but very good point.
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