Basement Flood: How to Adjust Downspouts and Grading to Prevent
LESLIE: Robin in South Dakota needs help keeping a basement dry. Tell us what’s going on.
ROBIN: I’d like to insulate the basement but before we do that, I’d like to seal it from water. Several years ago, I had dug up all around the outside of the house and put on that tar substance and that didn’t do it. So, I was just seeing if that spray-on poly spray would do both for me: both seal the basement up from some water coming in and also to insulate for me.
TOM: Do you have more water problems when you get a heavy snow melt or a big rainstorm or something like that?
ROBIN: Yeah, that is what’s coming in. It’s the rain. Actually, the rain hitting the foundation wall coming in is what causes it. It’s not groundwater coming up.
TOM: Well, typically the reason the basements leak is because when you have a heavy rain, water collects around the foundation perimeter. And many folks do try to seal walls from the outside or from the inside but we found it far easier and more effective to simply take some steps to divert that water away from the walls.
If you take a look at our website, MoneyPit.com – in fact, on the home page, this is – we have the list of the most viewed articles. This is constantly in the top 10 articles and that is the step-by-step advice on how to stop a wet basement.
But generally speaking, you’re going to do a couple of things. First of all, you’re going to examine the foundation perimeter of your home and look carefully at the grade. You want the soil to slope away about 6 inches over 4 feet. So you want kind of a 10-degree slope. And you want to make that slope happen with clean fill dirt, not top soil because it’s too organic.
Secondly, and perhaps most importantly, you want to take a look at your gutter system. First, you need to have enough downspouts. You need 1 downspout for every 600 to 800 square feet of roof surface. Next, those gutters obviously have to be clean and the downspouts have to be extended 4 to 6 feet away from your house.
Now, most of the time when downspouts are installed, they turn into a splash block and go out maybe a couple of feet. But what happens is the water runs down there, does a U-turn and just saturates the foundation and leaks through the block wall, which is very hydroscopic, very absorbent and will show up as a leak inside.
We’ve seen situations where just one downspout can cause an issue of flooding. And that water can either come through the wall and fall or it can go under the floor and come up. But if your basement is leaking consistent with rainfall, it is always, always, always due to grading and drainage on the outside. So address that and your problem will go away.
ROBIN: OK. Sounds good.