Basement Waterproofing

rain gutter

The first step of basement waterproofing can be found on the roof. Gutters are intregal in keeping your basement dry. (Photo courtesy of Craig E.)

Start at the Roof

Basement waterproofing is a complex subject, so before you hire a professional to fix that leak, learn what to expect with 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.

Ground-Level Problems

Basement waterproofing methods range from the simple to the complex, and can sometimes be costly. However, DIY basement waterproofing is not recommended by professionals; this is the kind of job that requires a qualified basement waterproofing contractor. The soil around the home should always slope away from the foundation and a declining slope of six inches for every six feet away from the home is preferred. However, this is not always possible.

Therefore, a French drain system may need to be installed where the soil slopes down towards the house, diverting water flow away from the home. The water can then be drained away from the house if a downgrade is available. It can also be emptied into a storm sewer or pumped away from the house. If the land surrounding the home has a downgrade towards the house, it may be necessary to install ditches where the slope meets your property.

When installing patios, porches, sidewalks or driveways, it is important to make sure the concrete or other material slopes away from the basement. Any flat surface that slopes towards the basement foundation will allow water to drain down beside the foundation. Adjoining edges should be sealed.

basement waterproofing graphic

Below-Grade Options

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.

A variety of basement waterproofing products exist for this purpose. Waterproofing paint is on the market, but should be used sparingly, and never as the sole waterproofing method. Sodium bentonite waterproofing uses a water-absorbing clay substance to fill cracks and prevent water from entering the basement. Crystalling waterproofing techniques are applied directly to concrete and make the concrete itself less porous. 

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.

basement foundation repair

To remedy this basement's failing foundation, the front area of the house was graded and a ditch/gravel drain system was installed. The foundation's walls were rebuilt with concrete blocks and rebar. (Photo courtesy of Angie's List member Lillian K.)

Damage to Walls and Floors

When the interior walls of a basement begin to bulge inward or the concrete floor begins to show cracks, it is probably due to improper or adequate water control. The first signs of a bulging wall are loose mortar joints or cinder blocks that stick out farther and surrounding blocks. The hydraulic movement and pressure of groundwater and saturated soil cause this bulging. Cracks in the concrete floor of the basement indicate movement of the soil below it.

Porous soils, especially clay, do not maintain consistent moisture content. As the clay becomes moist, it expands, and as it dries, it shrinks. This expanding and shrinking can cause the house to shift and settle. This is sometimes not discovered until a contractor is repairing water damage.

The contractor may state that the bulging walls will need to be reinforced. There are several methods of doing this and you may want to consult a structural engineer to determine the best solution. While reinforcement beams and struts can be used, it may not be the best solution in a finished basement. Additionally, replacing the entire wall is costly and does not always adequately solve the problem.

Wall plate anchors, approved by many structural engineers and building code officials, can be a more economical and efficient method of all repair. Because of their design, wall plate anchors require a minimal amount of excavation, can be installed more quickly than other solutions and are more aesthetically pleasing. The plate can be covered with paneling or drywall, using furring strips to elevate a wall covering above any mounting hardware. Whatever method is used, water control still needs to be addressed.

Cracked floors might need to be repaired by a process called slab jacking. In this procedure, access holes are drilled into the concrete floor and loose or liquefied material is removed. Quick-hardening slurry is pumped into the hole, bringing the floor back to level. The holes are sealed and the mixture is allowed to dry before use.

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