If anyone has expertise in on this subject, I welcome your opinions. A few years ago, I sealed a 15×15 basement crawlspace using a vapor barrier over which a lightweight concrete product was poured. The floor has been dry since installation. Whenever it rains, water weeps through the base of one side (exterior side) of the wall and when it dries, a white residue remains.
How do I fix this drainage problem? My house (30 yrs. old) sits nicely on the side of a gently sloping hill. The problem is that when it rains, some of the water flows from the street and onto my driveway/lawn and eventually seeps into this basement foundation wall. Another issue is that my neighborhood has a huge amount of ledge which I suspect contributes much to this problem. Also, I’m curious as to why builders sometimes leave a dirt basement crawlspace instead of pouring a concrete floor? In my case, I surmise that there may be ledge there since the floor slopes dramaticaly upward – on one end there is 7 ft. of clearance and on the opposite end there is about 4 ft. of head clearance. Thanks.
Replies
Just curious, you refer to ledge. Is that like a ledge of rock or a type?
Yes. I live in new England so there is plenty of massive granite/stone ledge.
A few ideas here. I think the best advice is to attack the water problem as far away from your crawlspace as possible. If your house is downgradient of a hill, you've got a surface water problem (as you noted). I'd think about trying to do some grading on your property to intercept the surface water periodically along the slope.
You may also have groundwater heading towards the house because it often mimicks the ground surface. That would be a little more costly to address. I think most new houses are (or should be) built with a french drain around the perimeter of the house to intercept this groundwater. Your house may or may not have one- if it doesn't, you'd need to excavate to the footer and install one- probably not cheap. Also, when you installed your vapor barrier in the floor, did you install any sort of french drain inside at the edges of the slab? Bad time to ask, but if you didn't, maybe sawcutting the concrete back and putting a french drain in leading to a sump would work for you.
Finally, it seems that one of the most recommended improvements for drainage is adequate gutters on the house. I've read that this can make a big difference in how dry the basement is and I know of at least one person who can actually tell when his gutters need to be cleaned out because his basement is noticeably more wet.
Not sure about the white residue- maybe lime leaching out of the concrete?
As far as why a crawl space wouldn't have anything more than a dirt floor, I'd suspect it's cost, which is also likely why a crawl space was used instead of a full basement. Besides, few things in life can compare to the joy of crawling into a dark, damp, dirt-lined area...
Edited 3/11/2003 12:54:17 PM ET by stonebm
Thanks. My comments are in [] after your responses.
A few ideas here. I think the best advice is to attack the water problem as far away from your crawlspace as possible. If your house is downgradient of a hill, you've got a surface water problem (as you noted). I'd think about trying to do some grading on your property to intercept the surface water periodically along the slope.
[One of the challenges is that my driveway is on this slope. I don't think it would be possible to intercept the the surface water. Correct? I suspect that the driveway helps direct water to the foundation since it slopes down. I will be replacing the diveway in the next year or so. Maybe some time of drain pipe could intercept the water and carry it out to the street? I'm not sure if a drywell would work since they seem useless once the watertables have maxed.]
You may also have groundwater heading towards the house because it often mimicks the ground surface. That would be a little more costly to address. I think most new houses are (or should be) built with a french drain around the perimeter of the house to intercept this groundwater. Your house may or may not have one- if it doesn't, you'd need to excavate to the footer and install one- probably not cheap. Also, when you installed your vapor barrier in the floor, did you install any sort of french drain inside at the edges of the slab? Bad time to ask, but if you didn't, maybe sawcutting the concrete back and putting a french drain in leading to a sump would work for you.
[You're right, it's too late. And cutting the concrete would eliminate the seal and probably lead to the rest of the floor breaking apart over time. The concrete is a proprietary product - very light weight. As I said, the house is 30 yrs. old so the only evidence of a Fr. drain is a sole drain in a corner of the basement far from the crawlspace. ]
Finally, it seems that one of the most recommended improvements for drainage is adequate gutters on the house. I've read that this can make a big difference in how dry the basement is and I know of at least one person who can actually tell when his gutters need to be cleaned out because his basement is noticeably more wet.
[Yes, I have optimized my gutters/downspouts and clean them every year. I even installed a few drywells]
Not sure about the white residue- maybe lime leaching out of the concrete?
[Yes, you are correct]
As far as why a crawl space wouldn't have anything more than a dirt floor, I'd suspect it's cost, which is also likely why a crawl space was used instead of a full basement. Besides, few things in life can compare to the joy of crawling into a dark, damp, dirt-lined area...
[90% of my basement is finished with a level concrete floor. Wht this raea was left unfinished is a mystery. I think it has to do with massive ledge. Why spend the $ on blasting? Maybe that was the builder's thinking]
Concrete is great for producing runoff (I'm being sarcastic). I'd bet even in a light rain, you can see sheets of water running down your driveway. I think including some sort of interceptor drain in the driveway is a good idea. You could cut one in any time but it'd be a lot easier if you did it when you replace the driveway. You should look for a continuous drain (I think they call them a "trench drain" or something). It basically extends all the way across your driveway to intercept all runoff from the driveway. The next thing will be to see if you can daylight the pipe somewhere without causing another drainage problem.
I generally agree with you on dry wells. However, they can work if 1) they're big enough 2) the soil drains well (or the well is huge) and 3) the water table is sufficiently low. How much the water table affects the well will depend on how deep the well is (obviously). Keep in mind that one single rain storm isn't likely to raise the water table all by itself- usually water table fluctuations are seasonal in nature. If the water table is at least 4 feet below ground, I'd say you could make a dry well work. Being in the northeast and having large rock outcroppings nearby, the soil is probably granular and will drain well- you could check it by doing a "perc" test like they do to site a septic tank. Not sure of the exact procedure, but you want to dig a small hole and fill it with water and measure how rapidly the water surface drops.
Yes, I too was thinking about a continuous drain across the bottom of the driveway with a steel grit/grate cover over it. ideally it would empty into a pipe the spills into a street storm drain. Thanks.
Regrade driveway to collect water in a catch basin provide a 12'' min. sump in bottom of catch basin to allow silt and dirt to drop into basin without flowing into pipe. Create positive drainage from house and if possible direct to catch basin. Excavate to top of footings and install drain tile with pea stone surrounding pipe, cover pipe and stone with geotextile fabric to minimize silt clogging pipe. Daylight pipe or tie into sump pump in crawl. Ideally you would like to have drain on interior of wall ,but seeing how you already have a slab poured, it is possible that this fix may be sufficent, if not you can always saw cut perimeter and install interior drains.