The footprint of my house is approximately 1500 sq. ft. of which about 400 sq. ft. is basement and the remainder is crawl space. Having read that it is a good idea to cover the dirt crawl space with a vapor barrier, I installed blue tarp over one 500 sq. ft. section. Since then in the summertime the bottom of the basement wall next to this covered area is quite damp. Also, when I lift the edge of the tarp the dirt under the tarp is very moist.
My question is: Have I done a good thing or bad thing by installing the tarp over the crawl space? Any ideas?
Ken_r
Replies
The object of the plastic over the dirt in the C/S is to reduce the amount of moisture that moves into the crawlspace thence into the floor system and eventually on up through the house and out the attic.
Depending on your location/weather/temperature that extra humidity may cause a number of potential problems. Mould & Mildew, warped wood members, ice formation in the attic, sweating of forced air A/C ducts, excessive condensate from the A/C, musty smelling basement, buckled hardwood floors.....ETC.....et.al.
For some good insight go to http://www.buildingscience.com !!
No, you probably have done nothing wrong in applying a band-aid. You should actually pursue the souce of the water saturated soil...it would be best if it were powder dry.
The wet spot on the wall may be the saturated air moving from under the tarp to condense on the colder wall surface....or you have a leak in the perimeter of the house foundation or from the gutters, or a negative grade landscape, or an underground spring, or a leaking water or septic line, or........etc..etc.. any of which is keeping the C/S wet. Wet is not good.
...............Iron Helix
The ground water level is roughly 8 feet below the level of the basement floor and perhaps 12 feet below the ground level in the crawl space. It hasn't rained here in the San Francisco Peninsula area since March or so. There is no water source near the basement wall. My guess is the water is rising through the soil from the ground water and the soil under the tarp is wet because I have blocked water vapor from rising thru the house. And incidently, before I installed the tarp my wife did complain about a slight mildew smell in the area above the crawl space covered with the tarp.
ken_r
There is a neat article within the last year or two in FHB about totally sealing the C/S with a membrane. Might look it up to have an idea about TOTAL moisture control.
You might consider sealing that blue tarp to the foundation wall with mastic to really seal out that moisture. Likewise complete the install of more blue tarps over the rest of the crawl space.
If you have an opening between the C/S and the basement you could allow for an A/C duct to be slightly open at the far end of the C/S which would then return back to the central unit in the unit inthe basement area. This would act as a dehumidifier for the C/S.
Yes, you live in a warmer dryer environment than I do ....we get over 40 inches of rain per year here in deep southern Illinois plus very high humidity, all of which makes most C/S's that I see moist to sopping wet.
..............Iron Helix
is the C/S vented? just wondered...........
sam
VENTILATE; A minimum of 1 sq ft of vent opening to every 500 sq ft of crawl space floor area. Hube
Where'd you get that number? Last I checked code was 1 sq ft vent per 150 sq ft floor area. We recently went to the IRC here and I have not specifically read up on that yet.
1 sq ft for every 150 sg ft of floor space. One opening within 3 ft of each corner.
My house which was built in about 1930 has 5 vents, each of which is probably about half a square foot.
Basically, my concern is more with the extremely damp soil under the vapor barrier. Can this cause some kind of foundation problem?
ken_r
Depending on your soil, wet/dry cycles thru the seasons can causing settling of the building, seen as foundation cracks, doors that don't open/shut, windows getting tight, plaster cracks, floor sloping, etc. If you're on clay it's more problematic. You shouldn't have much moisture under the house. What if any drainage is installed around the perimeter?
Assuming 1930 standards, there is absolutely no drainage around the foundation. However, it is almost 75 years later and the house hasn't rotted away yet.
Ken_r
Just out of curiosity.....where or why did you acquire/have the "ground water level" numbers for your 75 yr old house?
Very rarely do I have access to that type of info unless the there is a "spring" bubbling up in an old basement floor or the new basement excavation fills with water during the dig!
And no one here does site bores for soil composition or water table levels...too thrifty! Prefer to deal with it after the fact, even if there are warning signs.
As far as your concern with damp soil and your 75 year old foundation.... First I would agree that the current condition of the house and foundation as its "history" would be a reasonable indicator of the future.....Secondly if I were wanting factual info to settle my mind, I would seek out a soils specialist/engineer to give you the characteristic of your damp soil.
As an example....locally we have a clay hardpan that digs like concrete, but as soon a it is saturated with water to its point of plasticity it flows like grease. Footings set in this clay must be kept free from standing water. Strange things happen, especially for houses built on the sides of hills. They slide and settle.
Start with a local university geology department, or the US Department of Ag, Soil & Water Conservation for an insight to the soils in your area. Most county USDA's have soil maps and resources for more info ....gratis from your tax dollars. In the phone book under U.S. government.
..............Iron Helix
Thanks for the info, everyone.
To satisfy your curiosity as to my knowledge of the ground water level. I have a 20 foot deep well in the basement floor which supplies water at 12 gpm to a 5 ton geothermal heatpump which supplies the house with economical conditioned air. The used water is then dumped in another well approximately 50 feet away from the house.
Ken_r
Hey.....that's cool! Several puns intended!.........Iron Helix
Depends on the roof slope.
2/12 or less is 1 ;150
3/12 or more is 300
Thread is about crawl spaces under the house...