Angie's LIST Guide to
Basement waterproofing

Interestingly enough, waterproofing the basement begins at the top, on the roof. The main purpose of a home's gutter system is to redirect roof runoff so that the area around the foundation is not saturated by rainwater during a downpour. Homes with no rain gutters, or with inadequate or inoperable gutters, are at risk of being damaged by water.

Gutters must be sized large enough to handle the volume of water that will run down the roof during a rainstorm. Additionally, they should be installed on every roofline that is parallel to the ground, not just over windows and doors. It is important to ensure that the gutters are properly sloped towards a downspout during installation.

Because an average house roof can shed upwards of 2,000 gallons of water during a heavy downpour, buying oversized gutters is a smart choice. Of course, a properly guttered roof will still be inadequate if the guttering is full of leaves or debris. Therefore, the homeowner must be responsible for regular cleaning.

Moving down, the next order of business is the downspout system. The homeowner should not scrimp on downspouts. Downspouts should be adequately sized to handle the volume of the water in the rain gutter; there should also be enough of them for efficient rainwater removal.

The bottom of the downspout should divert the water away from the foundation of the home. Ideally, the water should be diverted between six and ten feet away from the home on a grade that slopes away from the house. In locations where a downspout cannot be installed, the use of splash blocks can help divert water away from the foundation.

Below-grade waterproofing solutions are easier to implement during construction; however, many of these options can be done on an existing home. The exterior walls of the basement can be coated with a waterproofing substance. Petroleum-based products have often been used, but newer technologies exist that paint the block with a sealant that is overlaid with a waterproof covering or vapor barrier.

An increasing popular option for waterproofing existing homes is to install drainage systems around the bottom of the footing and under the concrete floor of the basement. The drains can be constructed of perforated PVC pipe, encased in a filtering cloth. They are installed on a sand base for cushioning and additional drainage and are covered with a layer of gravel to allow water to drain into the pipe. The cloth prevents debris and rocks from clogging the drainpipe.  These hidden interior drain pipes are typically then directed to a sump pump.

While these solutions are best implemented at the time of construction, it is still possible to install the drains after the home has already been built. It will be more expensive, however, because extensive excavation may be necessary to install the drain system or apply the waterproof coatings.

Nevertheless, this expense may offset the inevitable cost of interior repairs and cleanup, especially if leakage or flooding occurs frequently. In finished basements, cleanup costs will be considerably higher because of water damage to furniture, utility equipment, interior room walls and wall coverings.