When Rainwater Seeps Into Heating Ducts

QUESTION: My house is built on a concrete slab. About five years ago, after a long hard rain or sudden deluge, we began to get water seeping under the slab and into the floor-heating ducts. Water enters the ducts on the side where the ground slopes upward, then fills all the other ducts. Is there any way to stop this water from entering the house?

ANSWER: The best way to control the problem is to intercept the water before it gets under the slab, and direct it away from the house. But, before you go to the expense of putting in a subsurface drainage system, check other possible solutions that are less expensive.

The ground immediately adjacent to the house should be graded so it slopes away from the foundation. There should be eight inches of minimum distance between the top of the foundation where the sills rest and the grade level. The eight-inch space will prevent rain from splashing up, soaking the wood and possibly rotting the structure.

The down slope stops water from collecting around the foundation and it also forms a swale, or depression, to carry surface water away from the house. To accomplish this, you may have to move quite a lot of earth but it may be easier than installing a drainage system.

If you do not have gutters to channel roof rain runoff away from the house, they should be installed. If you have gutters, make sure the downspout bases extend far enough away from the foundation or install splash blocks to prevent rain from collecting there.

If surface water is not the cause of your problem, you will have to intercept the subsurface water before it gets to the foundation. This can be done by installing a curtain drain parallel to the house on the slope that runs toward the house.