# Gravel crawl space. Plastic vs concrete



## gregzoll (Dec 25, 2006)

You can use a Dehumidifier to pull the moisture out of the space, and also keep it vented.


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## concretemasonry (Oct 10, 2006)

A good thick layer of poly (6 or 10 mil) would be better than concrete if you are concerned with the general moisture from the soil.

If you have water leakage, a slab (with poly under it) and possibly drain tile would be a solution after you have looked closely at your exterior drainage and gutter downspouts.

Dick


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## howard.wheaton (Oct 7, 2008)

The concrete solution will be a 10mil plastic on top on the gravel and then the concrete placed. May I ask why plastic is a better solution then concrete? I am looking at permaseal also and their plastic goes up the concrete wall 3" from the top. They sell it as a reverse pool liner.


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## howard.wheaton (Oct 7, 2008)

gregzoll,

They are actually now saying that crawl spaces should be sealed and vents closed or sealed. When warmer or cooler enter enters a crawl space, the change in temperature increases the humidity, which increase the moisture content.


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## concretemasonry (Oct 10, 2006)

Howard -

Who is "THEY"? A change in temperature does not increase the humidity and it just increases the ability of the air to hold moisture. The dew point is the inportant measure.

Unfortunately, you did not say where your are or what the climate is like. Do you have an actual problem of just a fear of going the wrong way?

Humidity is not a problem if it does not create the condensation that can cause loss of insulation (in fiberglass) or even rot/mold. In many situations, a well ventilated crawl space can be very effective. In some climates, it is advised to have operable vents for seasonal (not daily) variations.

Vapor barriers (actually vapor retarders) are used to prevent condensation at the dew point. Generally, they only apply to heating conditions where you have a cool climate and not just a cool night. Vapor barriers are applied to the warm side of the insulation in these situations.

For some professionals, concrete can supply moisture or dry it out since it is a valuable source of temperature and moisture control/moderation in some instances.

Dick


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## howard.wheaton (Oct 7, 2008)

I live in Chicago and looking at either permaseal or concrete floor. I just moved into a house in January. I don't really have a moisture problem and the wood looks fine in this this 1977 house. We had 9" or rain here and the rocket scientist that lived here before me had the check valve reversed so when the exterior drain tile drained into the sump, it kicked on, but nothing happened and the sump over flowed (had 5" water discoloration along the wall so I know it flooded) . Not sure if water came through the gravel floor or not, but i assume that it was caused by the sump overflowing. The gravel has been dry with other rains so I assume all is good. when I bought this place I knew I wanted to do something in the crawl, but the big rain moved it up the list.

I was doing some poking on the wed and the gov't just released a brochure on crawl space and local code also changed to indicate that vented crawl spaces are no longer a good idea if you have taken care of moisture coming from the ground. I am torn between the "pool liner" solution or installing 304" on concrete. Both solutions would have an interior drain tile installed and draining to sump. Any thoughts?


Thanks!


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## gregzoll (Dec 25, 2006)

The change is only on new construction. Since you are in an existing structure, then you should be grandfathered in. After the rains in Sept., there was nothing that you could do to stop the flooding, other then get out the canoes & John Boats and have fun.


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## howard.wheaton (Oct 7, 2008)

thanks. Local codes stated that crawl spaces should be sealed on new construction and recommend that if moisture barrier (concrete or plastic) is install on old homes, that the vents are to be sealed up.

would you recommend plastic or the concrete as a permanant solution?

How about installation on the walls? Does anyone have any recommendation? I am going to place R-19 unfaced along the sill plate, but not sure what to place on the walls.


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## Wildie (Jul 23, 2008)

I have a cottage about 500 miles due west of Chicago and it has a crawl space.
I built this place back in the 70's.
I placed 6 mil plastic over the earth and had the recommended venting.
Eight years ago, I had a new furnace with a/c installed and this included conditioning of the crawl space. With this in mind, I closed the vents and installed R12 insulation on the walls.
I have since found that the area is much dryer ( no need for dehumidication)
Research has shown that more moisture comes from humid air flowing in from outside, rather than being wicked up from the ground.
I would expect that this would be dependant on the soil condition and drainage.
In my case there is about 24" of clay, another 24" of sand and then at least 12' of gravel, so i have very good drainage.


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## howard.wheaton (Oct 7, 2008)

What type of insulation did you use? fiberglass (faced or non-faced), foam board, spray, etc...


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## Wildie (Jul 23, 2008)

howard.wheaton said:


> What type of insulation did you use? fiberglass (faced or non-faced), foam board, spray, etc...


 I used Roxul bat insul, held in place by adhesive pins!

read about em here! http://www.wipo.int/pctdb/en/wo.jsp?IA=US1994002115&DISPLAY=DESC


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## NW Indiana (Oct 27, 2008)

*concrete in crawl*

The discussion was helpful about gravel vs. concrete in the crawl. Same decision for me in the gravel crawl. The exterior drain tile that exists, original to home (45 yrs), runs right through the middle of the crawl space. After inspecting a length of 12" drain tile, is it safe to pour the 4" of concrete over tile, or should we leave open a 6" gap in the concrete to access this tile in the future? Also, is adding interior drain tile for hydrostatic pressure plus the existing exterior drain tile overkill? Building inspectors and contractors haven't been much help with this.


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## howard.wheaton (Oct 7, 2008)

Just to give an update, I had 4" of concrete poured in my crawl space, placed R-19 insulation along the walls and sill plate and sealed up the vents (per buildng code for new homes and DOE recommendation). It has worked great. It is 62 degrees and humidity level is 42% and it is 18 degrees and 91% humidity outside. I have a dehumidifier down there and it very rarely kicks on.


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## NW Indiana (Oct 27, 2008)

*concrete crawl*

Thanks for the update, we also went with about 3 inches of concrete in the crawl and so far working nicely.


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