Water Seeping Under Foundation: How to Improve Drainage
LESLIE: Bill in Virginia is dealing with a wet basement. Tell us about the problem.
BILL: Yes, hi. My house is built like 130 years ago.
BILL: And I have water seeping in through under my foundation; through under the floor and through the bottoms of my foundation. I want to know what kind of product – is there any way I can fight that from inside?
LESLIE: Now Bill, do you find that the water is only coming in when there’s a really bad downpour going on outside?
BILL: Primarily when there’s a high water table. So yes, after we’ve had quite a bit of rain, the water doesn’t necessarily come in when it’s raining but if the water table rises, then it comes up through my floor.
TOM: So Bill, would you say it comes in maybe a couple of days or more after the heavy rain?
BILL: It can be a couple of days after the heavy rain or when we’re having the heavy rain, depending upon the water table.
TOM: Yep. OK, so here – let me explain something to you because you made a statement there which is a very, very common misconception. You think that it’s associated with the water table. It’s not. The water table doesn’t move that quickly. The water table moves seasonally. What you are seeing is a drainage problem that’s triggered by the heavy rain and the fact that the water is not being diverted properly away from the home.
When you have water that – a water problem in the basement that is consistent with rainfall, with melting snow or anything of that nature – and when I say “consistent,” it could happen during the rain or it could happen a day or two or four or five days after, when the ground is very saturated. That water saturates and soaks in that area right around the outside of the house, which is what we call the backfill zone, and it will either come straight through the wall or it’ll push under the foundation and come up through the floor.
The good news here, Bill, is that it’s an easy problem to fix. You have to improve the drainage around the house. Two things to do. Number one – I want you to examine the soil around the outside of the house. If it’s flat, you need to add more and slope it away from the walls. Now don’t add topsoil because that’s too organic and the water will stay trapped against the house. Add clean fill dirt. The slope that you’re looking for is a drop of six inches over four feet; about a 10-degree slope. So, establish a good slope there.
And the second thing, which is even more important than the grading, is to look at the gutter system. Do you have gutters on the house, Bill?
BILL: Yes, I do. They’re brand new.
TOM: Make sure that they’re clean. OK? Make sure that they are free-flowing and make sure that the downspouts are extended out away from that house at least four feet; not just a little turnout at the bottom and a little splashblock that takes the water out a couple of feet. I want it to go at least four feet.