Solving Basement Water Problems

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Figure 1: Idealized basement to keep out water leaks.
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Figure 2: Inside drain for high groundwater.
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Diagram: Problems in home basement that could cause water leaks.

Laid-up masonry basement walls on concrete footers are sturdy, economical, and comparatively simple to erect. Combine those attributes with the fact that they allow great design flexibility, and you’ve got a pretty fair explanation of why concrete block basement walls are so common. Unfortunately, water leaks all too often seem to be another standard feature of block basement walls.

Solving Basement Water Problems

Once you’ve determined where the water in your basement is coming from, follow the key numbers to find solutions appropriate to your problems. Try the lowest-numbered solutions first, and move on to more drastic measures — such as digging up the foundation and installing a drain — only if the easier approaches fail.

[1] Landscaping

The simplest, least expensive way to solve surface water problems is to landscape the area around your house to prevent surface water from saturating the soil next to the basement walls. The ground should slope downward from the house at least 4 inches in the first 6 feet, and no shrubs or trees should be planted closer than 3 feet from the walls.

In a location where the terrain itself slopes significantly, it may not be practical to grade the entire area around the house to reroute drainage. In such a case, a shallow valley can be cut about 12 feet out from the wall to catch runoff and route it around the house. This depression need not be severe; a 1-foot-deep trench with gentle sides will channel a great deal of water and will still be easy to mow.

[2] Water-shedding layer

If you’re forced to strip back more than a few inches of topsoil to achieve the proper grading, it’s probably worthwhile to continue digging down to a point about a foot below the previous grade, and to then lay down a sheet of 10-mil polyethylene before replacing the soil. This barrier will usher water away from the basement walls.

[3] Redo sidewalks or porches that are poorly sloped or loose to the foundation.

It may sound drastic to rip up a sidewalk or porch and replace it, but this is still a much easier undertaking than uprooting the house’s footings. Break up the old concrete, and dig down 4 inches below what was the level of the underside of the slab. Lay a 4-inch layer of gravel for drainage, and set the forms for the new concrete so that the new slab or sidewalk will slope away from the foundation wall about 1 inch in 10 feet. Use a watertight expansion joint between the new concrete and the foundation wall.

[4] Investigate and repair the perimeter drain system

Unless you live in a very dry area, your home’s foundation should have a footing perimeter drain. There are two general types: On lots with sufficient slope, the drain may work by gravity, emptying out into a storm sewer downhill from your house’s foundation. On level terrain, the perimeter drain should be tied to a sump pump in the basement by drain lines that run under the footing, as shown in Figure 1 (See water problem diagrams in the image gallery).

Sump pump systems: If you’ve got a sump pump, you’re also almost certain to have a perimeter drain. In this case, if your pump is working but you’ve still got a water problem, at least a portion of the foundation drain isn’t flowing properly to the sump.

Gravity systems: Lacking advice from the builder or original owner, you may not find it easy to figure out whether your home has a gravity drain system. To confirm its existence, you’ll have to either locate the outlet for the system or dig down and look. If you find no drain, it’s time to call in a pro with a backhoe and have him or her put one in.

Assuming that you have a drain system and that all the accessible portions are in good or der, the difficulty may be that a section has become plugged or has collapsed. Either is a serious problem, but it still may not be necessary to uproot the whole foundation. If you can pinpoint where water is leaking into the basement by examining the inside of the wall, there’s a good chance that the problem area will be directly outside.

Barring that, you can test the drain system from the outside with a garden hose. Sump pump systems can be probed by attaching a 6-foot length of steel 1/2-inch water pipe to the hose and using the jet of water to bore down to the footing. Move around the basement walls in 6-foot intervals and look for locations where water doesn’t get to the sump in the basement. For gravity systems, just saturate the soil next to the exterior basement wall in a suspected area for several hours. If you get a gusher inside, you’ve found a good place to start digging.

[5] Add a perimeter drain system and sump pump

This is no small undertaking; you may want to consider hiring someone with the proper tools to do it for you. Nonetheless, here are the basics: Start from inside the basement by cutting a hole for a sump in the concrete slab about 2 feet from the basement wall. This hole will need to be about 2 feet in diameter, but you should find out the exact size of the sump tile (clay, concrete, or plastic) from your plumbing supplier.

Before placing the tile, dig a horizontal 6-inch-diameter hole under, and to the outside edge of, the footing. Place a section of 4-inch plastic pipe in the hole, and then complete the sump pump installation. By doing this work first, you’ll be sure that any rain that arrives while the footing is exposed will head straight for the sump.

A small backhoe will cut the time and effort needed to dig up the footings by several orders of magnitude. But if you’ve got a strong back and plenty of perserverance, you can save quite a bit of money by hefting a shovel yourself. Whichever approach you choose, start where the 4-inch pipe passes under the footing and dig a tapering trench all the way to the bottom of the footing. At the bottom, the ditch should be 10 to 12 inches wide to allow room for the tile and gravel. Continue around the house, tunneling under sidewalks when you can or leaving out the drain where it’s impractical to go under a larger section of concrete. Once the trench is finished, clean the wall thoroughly, and use Figure 1 (See water problem diagrams in the image gallery) as a guide for installing the drain, the waterproofing, and the backfill.

[6] Install a slab drain system for high groundwater

If your water problems stem from a rising water table, a perimeter drain alone won’t dry out your basement. You need a way for water to get to the sump from both inside and outside of the footings.

What I’m about to describe involves backbreaking labor — yours or your employee’s — but I don’t know any way to get around it. You’re going to remove a 3-foot-wide section of your basement floor all the way around the inside perimeter of the basement walls.

Start by breaking out the floor and digging the hole for the sump pump, and then work along parallel to the wall removing a piece of the slab at a time in a 3-foot swath. This will go more quickly and easily than you might think if you’ll undermine a section of the floor with a shovel to the depth of the shovel blade and then break the unsupported slab with a 10-pound sledge.

Use Figure 2 as a guide (See water problem diagrams in the image gallery) for installing the gravel and drain tile and repouring the floor. Be sure to include the weep holes and the inch of gravel on top of the footing and the weep holes so that water can drain from the block cores to the sump. Keep the new concrete — mixed at a ratio of about 1 part portland to 4 parts fine, clean gravel — level with, or about the thickness of a sheet of paper higher than, the adjoining old concrete.

[7] Install a block drain system

One solution to water that’s draining down through block cores to leak out between the joint of the wall and the floor is to drain the block cores to a sump pump. Go up about 4 inches from the floor to avoid mortar that may have dropped to the bottom of the cores, and drill a hole in each block core. Caulk a short piece of plastic pipe into each hole, and plumb the drains together with appropriate Ts so they lead to the sump. Observe proper drain slope of 1/4 inch per foot, so that water doesn’t back up.

EDITORS NOTE: Harold W Dickinson is a building inspector in Olivia, Minnesota.