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My house is located in Missouri, currently I have a vented crawl space with a dirt floor. My home was built in 1998. I put a humidity tester in the crawl space and it reads anywhere from 75%-88% humidity at all times of the day. The living area hovers around 60% humidity.

I received a quote from a local company to fix the issue for $10,000.00, needless to say, I have decided to try and fix it myself first. Note, their solution only involved fixing the crawl space, they did not even mention fixing outside water issues.

The crawl space has a sump pump in the lowest corner, with a drain tile on the entire lowest side leading to the sump pump.

The house is on a slope, where the front of the house is the highest point, and the back of the house slopes down. The front of the house faces North.

All of the gutters go underground, and drain the water 5-6' from the house. The pipes which transport this water are always full of water, but when it rains they do seem to push water out.

The front of the house has no downspouts (they are on the sides), and during a downpour water overflows over the front gutters, then gets into the crawl space on the north side. After it rains, the front gutters still have 1/2" standing water which eventually evaporates. (I think the slope is wrong).

I also have a faucet on the front of the house, if this faucet is on for any amount of time, and drips onto the ground on the front of the house, this water also makes it's way into the crawl space.

  1. I find it odd that there are no downspouts on the front of the house, though this might be because of the slope?

  2. How should I deal with this humid crawl space?

  3. Note being Missouri the crawl space is super rocky, to the point where it would be impossible to remove all of the rocks, will 6 mil vapor barrier be OK on top?

After much research I came up with the following:

  • Fix front gutters so they do not overflow (either increase size, or fix slope)
  • Remove the handle from the front faucet so it is never used.
  • Seal Crawlspace Vents
  • Lay 6 mil vapor barrier, stake down with garden stakes (currently not planning to go up the walls)
  • Seal the top of the sump pump bucket
  • Install dehumidifier that will run continuously and drain into the sump pump (Frigidaire FFAD5033R1)

Does this seem like a sound plan? Any advice would be greatly appreciated.

More Information:

  • Currently there is about a 1/2" of standing water in the crawl space on the very north side.

  • I have done a thorough inspection, and crawled through the entire crawl space and there is no wood rot, the soil is damper in the center, and north side of the crawl. It smells like a cave, and this smell seeps into the living area. My hardwood floors have slight cupping.

  • Hello, and welcome to Stack Exchange. Please add new information to the question, rather than putting it into comments; it makes it easier for readers to understand what's going on. – Daniel Griscom Oct 25 '16 at 0:52
  • I have fixed that. – user1625155 Oct 25 '16 at 1:13
  • Does water run down the slope towards the north wall of your house? Could you ventilate the crawl space, perhaps adding insulation between the crawl space and the house? – Daniel Griscom Oct 25 '16 at 1:40
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Here is the solution I implemented to fix this issue and ultimately brought the humidity level to a stable 58%:

-First and foremost the first thing I did was get a Meade Instruments TM005X-M so I could measure the humidity levels in my crawl space and get a baseline. My starting humidity levels were 75%-88%, most likely hitting 100% over the summer.

-I Had a contractor come out and replace gutters, adding two downspouts to the front of the house. In addition I will be digging trenches to send the water at least 10 feet away from the house. This was necessary because there were no downspouts on the front of the house and the water would pour over the sides of the gutters.

-I then laid out 6mil black plastic on about 75% of the dirt in the crawl space. This alone lowered the humidity from 88% to around 75%. I did not remove all of the rocks, and even after crawling on it with kneepads it did not break or tear the plastic. We did remove some of the obnoxiously large Ozark rocks. The 6mil plastic (recycled even) ($75.00) is very strong. I did a 12"-24" overlap and did not seal the seams. We did not go up the wall. We staked it down with garden stakes ($8). It is by no means perfectly sealed, but is covered.

-I sealed up all of the crawl space vents (6) with 1.5" foam, and used expanding foam to make sure the seal was good. ($30.00)

-I installed the humidifier and set it to run in continuous mode. The humidifier model I ended up getting was the FFAD7033R1 which can run in continuous mode by hooking a hose up to it. This hose drains to the sump pump. The sump pump did not have a lid, so I purchased a standard 5gal bucket lid and used waterproof duct tape to seal the lid onto the sump pump, then drilled a hole in it for the hose to come through. This put us around 65% humidity. Later I will set this to a specific humidity to hold at, and it will only run when needed. ($250.00)

-Finally, we covered the final 25% of the crawl space with the same 6mil plastic. During this time we discovered standing water, a couple 1/4" deep small puddles near the front of the house (north, the bad spot). At this time I inspected the area thoroughly and found that the sewer line going through the foundation and out had no sealer around it. This left a 1/2" gap around the entire pipe, going directly to the dirt. Under the pipe there was mud-like residue, so I was now certain this was the root issue. We used expanding foam sealer around the pipe, and laid the 6mil plastic over the puddles. This final step brought us to 58%, and I am confident it will continue to drop.

All in all, I was quoted $10,000.00 to fix this problem with a CleanSpace® system, and ended up spending around $450.00 max plus my time, about 20 hours to fix it myself. Note I don't count the gutters as included in the price since they were old and failing already. Also, the solution from the contractor did not include solving outside water problems, which in my opinion is where you should start.

Additional note about sealed vs unsealed crawl spaces. There is tons of conflicting information on this subject so I decided to test for myself. On a day when the humidity was around 55% outside, and the humidity was around 70% in the crawl space, I setup box fans to suck the 55% humidity air from the outside into the crawl space for around 12 hours straight. Doing this lowered the humidity only by 1-2%, so I knew sealing my vents was the answer.

It may seem counter-intuitive, but when dealing with crawl space issues START OUTSIDE.

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