We’re in the process of remodeling the basement of our 120 year old house, here in Chicago. The basement slab is about 4 feet below grade. We don’t get much water, just an occasional damp spot on the slab after really heavy rain. But the stone foundation walls do show some efflorescence and some mold, especially below grade.
I know that the only surefire way to eliminate moisture in the basement is to install a french drain system around the perimeter of the house, thus preventing any ground water from getting to it. Due to cost and other factors, this is not a step I’m eager to take right now. However, I am going to be re-landscaping in the spring, and am working out a plan to create an 8 – 10′ band of relatively dry ground around the perimeter of the foundation.
Here’s what I’m thinking:
Currently there are roofed porches that extend about 8′ beyond the foundation off the front and back of the house. I’m also planning to install a concrete or asphalt driveway along one side of the house, which will seal against the foundation. So three sides of the house will be done.
A yard area is on the fourth side of the house. Here I plan to slope the grade away from the house and extend the gutter downspouts out into the yard. In addition, I’m thinking of installing an 8′ to 10′ wide planter area along the whole length of this side of the house, fed by a drip irrigation system and covered w/a waterproof membrane sealed against the house. This would not prevent all water from getting through. But if done well should transfer 80% or more of surface water out away from house.
I’m wondering how far this approach seems likely to go toward resolving our basement moisture problem? Are there additional steps I could take (short of installing french drains) that I should consider?
Edited 11/20/2005 9:31 am by krx
Replies
Welcome to BT!
Are you sure your damp spot and mold aren't from high rh and condensation?
While I can't see your site, nor know anything about your groundwater levels, that shield you're proposing is exactly what we use to keep our underground houses dry. We go out a little farther from the perimeter, but that's for a different reason. All we use is 6 mil plastic, in multiple layers.
Typically we have hillside above the house and are careful to channel runoff around the house. Have never had any water problems. The last one, the client insisted on a traditional foundation drain anyhow. Never saw a drop come out of it.
If you click on your name, you'll find your personal profile, which you haven't filled in. Location is the most important thing so anybody responding will have an idea of your climate.
PAHS Designer/Builder- Bury it!
Thanks VaTom. I've now edited my profile, and original post, to reflect our location (just outside Chicago). It's flat as a pancake here and though I could be wrong I don't think there's much of a groundwater problem. The mold and efflorescence could be due to high RH and condensation, but wouldn't THAT be due largely to moisture my foundation walls/slab are wicking from outside to in? I've just installed a new HVAC system that now includes the basement, so we should be able to control the level of RH. Hopefully, combined w/the water shield above, that will keep us dry down there.Also, all of the mold/efflorescence is below grade. If it were high RH/cond wouldn't it be more uniform throughout the basement?I'm pretty sure the occasional dampspots on the slab are due to saturation of the ground outside and seepage through the foundation wall. It only happens after VERY heavy and prolonged rains (maybe once a year) and always forms in exactly the same spot. It's on the side where the driveway is going so hopefully it won't be a problem after that. As for the water shield in the yard, have you got any ideas about how to keep openings for plants from serving inadvertantly as drains? I'm thinking I'll plant the plants on little mounds and run a ring of round plastic edging in a tight circle around the plant (leaving room for it to grow, of course). The plastic would form a lip to keep run off from entering. May be a little labor intensive, but it's not a huge area to do this way.Thanks for the feedback, and I must say, that is one INTERESTING project you did there in VA (checked out your website). WOW!
Hmmmmm? Wow, I just did a bunch of digging to figure out how you found that page about our place. No secret, but I didn't set up that link. Big brother must be watching. LOL Glad you enjoyed your visit. It was put up, unbeknownst to me, by the guy sponsoring the accompanying forum, after exchanging emails. There aren't a lot of these around, despite the book being published in '83. BTW, 24º outside the other morning. House is still cruising near 70º, with us doing nothing. We're gonna try real hard not to be obnoxiously smug when we hear heating cost complaints this winter.
OK. Chicago, this time of year, means your basement walls are warmer on the lower buried parts, right? So with the upper walls colder, and water appearing on the lower parts, means it ain't condensation, as you pointed out. Move that house several states south and the opposite would be true.
Basements, unlike the one we live in, normally don't have many air changes or any rh control. Coupled with ground contact cooler temps during humid summers, the rh is normally very high. If your condition occurred during your summer, and not now, it'd likely be at least partly condensation on the cooler lower walls. Either way, controlling the rh will make a difference.
The normal test for condensation is to tape a piece of plastic to the wall (or floor) and see if it gets wet under it. I don't imagine your walls are flat enough for that.
Our umbrellas have enough dirt on top to support plant growth. We're in the middle of a mature hardwood forest. Amazingly, never occured to me that trees would try to get going there. Middle of the roof is a poor place for an 80' oak. I've got raised veggie beds up there and recently transplanted a bunch of wild raspberries to choke out the poison ivy on the rest. They'll compete with the volunteer tomatoes. No lawn mower lives here.
If you dropped your shield a foot or so you'd have enough soil to support the plants most people want close to their houses. Obviously a lot more excavation, but it works. Seems a little safer than having plant penetrations. "Flat as a pancake" means there's always going to be an issue of where the runoff's going. Clearly, farther from your foundation is better.
Sounds like a plan. Good luck.PAHS Designer/Builder- Bury it!
if you have effloresscence, it is NOT from condensation. Efflorescenece is minerlal salts being leached out by water moving THROUGH the masonry
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