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A couple of years ago we watched as our Midwestern neighbors experienced record rains and flooding. Next it was the West Coast that received all the rain.

Each year, it seems, record rains cause once-dry basements to leak and crawl spaces to flood somewhere in the country.Homeowners are asking: What causes a basement that has never had a water problem to suddenly start leaking? Is this a serious problem? Will it leak again? Can the water damage the foundation? How will I stop the water from coming in, and what will it cost?

Some basements have received serious damage and need immediate attention, and some need repairs that can wait. Others may not need repairs.

Most basements are built of hollow concrete blocks. In heavy rain, the blocks can fill with water and start to leak at the seams and cracks. Some walls leak where the basement floor meets the wall, and others leak up through the floor.

The reason basements have been leaking is simple: The ground is saturated with water.

Imagine your house as a boat trying to float, but with holes and cracks in its concrete block walls. Noah sealed his biblical boat inside and out with pitch, but your boat's walls are probably not sealed at all.

Once the groundwater level returns to normal, your basement may not leak until the next record rain. If so, you can afford to take a wait-and-see attitude.

But if your basement had a trickle before and now has several trickles, you should have it waterproofed. And if your basement floods often, don't wait for the next rain. If you delay, you may have to repair your foundation as well as waterproof your basement.

You will hear contractors use the terms "hydrostatic pressure." That is the pressure of groundwater against the wall and under the floor.

As the ground becomes saturated, the pressure builds. It can get as high as 500 pounds per square foot at the bottom of a saturated concrete block wall. Under that kind of pressure, water is forced through and under walls of basements that have never leaked before.

Some walls will develop a horizontal crack about two or three blocks down from the top. This is a normal crack - called a drought crack - and is usually caused by the expansion and contraction of soil around the house.

On the other hand, a horizontal crack near the middle of the wall is a serious problem and may need immediate attention.

There are two basic ways to waterproof a basement. One way is to stop the water before it gets to the wall and drain it away. The other way is to trap the water as it enters the basement and drain it away.

The proper choice depends on the style of home you have and the grading and drainage outside.

Homes on level lots are more suited to the interior drainage system.

The concrete floor is cut along the inside of the wall, a drain tile is laid in a bed of river rock, and the concrete is replaced. Water drains to a sump pump that gets rid of it.

Homes on sloping lots and split-level homes can be effectively waterproofed from the outside. The dirt is removed, a drain tile is installed in a bed of river rock, the wall is covered with a waterproofing mastic and a layer of plastic film and the dirt is replaced.

If you choose interior waterproofing, you can expect to pay $25 to $30 per linear foot of the four outside walls. There is also the cost of a sump pump and, in some cases, the costs of installing PVC panels on the walls; the panels are used when the walls are known to weep. They cover the wall up to a height of 4 feet, trap water behind the panels and direct it to the drainage system.

Waterproofing on the exterior costs $18 to $20 per lineal foot for areas less than four feet below grade and $32 to $40 per linear foot for deeper areas. The water can be drained by gravity, and a sump pump is not needed.

Most companies offer a guarantee good for the lifetime of the homeowner; a few will pass the guarantee on to a buyer if the home is sold within a set amount of time.

Walls that have serious cracks and walls that are bowed can be repaired by installing steel braces.

If the wall is bowed, it may need to be excavated and the blocks shoved back to an upright position. Steel I-beams used to brace the walls are about 3-1/2 inches thick, the same as a two-by-four.