The drainage inspection should begin as you are driving to the house. When you approach the house, notice the overall topography. Is it level or inclined? If it is inclined, is it a gentle slope or a steep slope? With inclined topography, you should be concerned about the possibility of surface and subsurface water
Perforated pipe movement toward the house. If the house is located near the bottom of an inclined street, is a storm drain (catch basin) in the street at the low point? There should be, especially if the street is paved. Otherwise, after a rain or a snowmelt, water accumulates at the low area and depending on the amount, can flood the adjacent yards and driveways. Did you notice a waterway (stream, brook, etc.) on the street as you approached the house? If you did, the house might be located in a flood plain.
When you arrive at the house, notice whether the land between the house and the street is above or below the street level. If the land slopes downward from the street to the house, the house is vulnerable to drainage problems. The surface water, if not properly controlled, can accumulate around the foundation or can pond on the lawn or over the entry path. If the house is inspected when it is not raining, you might not see any problems. However, based on the slope and overall grading of the land around the house, you can at least determine the potential for a problem.
As you walk around the house, notice whether the ground immediately adjacent is graded so that it slopes away from the house on all sides. It should be. Otherwise, surface water can run directly to the foundation (see FIG. 6-6), seep down along the foundation walls, and accumulate at the lower section. This usually results in water seepage into the basement or crawl space. A rule of thumb for grading this area is a drop of about 1 inch per foot. The lawn should slope away from the house for at least 10 feet and should be pitched so that there is approximately a 10-inch drop over that distance. (See FIG. 6-7.)
Because of normal soil settlement and compaction, clogged gutter or faulty downspout, and foot traffic (especially when the ground is wet), the slope of the ground adjacent to the house usually changes with time. Consequently, the area around the foundation should be periodically checked for proper grading.
Fig. 6-6. Improper grading of the land adjacent to the house. The lawn pitches toward the door, resulting in surface water ponding in front of the entry area.
|Minimum 8" clearance|
|Finish grade should slope 1" per ft.||Drain away from house|
|Fig. 6-7. Finish grade of the ground adjacent to the foundation, sloped for proper drainage.||Basement wall||10'||Original grade|
When checking the grading around the foundation, you might occasionally see a pipe protruding through the foundation wall or from a basement window. Record the fact on your worksheet for further investigation when you inspect the basement. Usually, this pipe is connected to a sump pump and is used for discharging the water that accumulates in the sump pit. The end of the pipe should be extended away from the house so that the water does not accumulate around the foundation. Sometimes the pipe terminates just beyond the foundation wall, which negates the advantage of a sump pump. The discharging water accumulates around and under the foundation and reenters the sump pit, only to be pumped out again. (See FIG. 6-8.)
If you find a stream on the property, you should realize the potential for flooding. As discussed previously, flooding can occur because of increased surface runoff resulting from a prolonged heavy rain. In addition, if the stream channel is blocked by fallen trees, tree limbs, sediment, or trash, flooding can result. Depending on the location of the stream relative to the house, occasional overflowing of the stream banks might or might not be a problem.
As you walk around, look at the overall landscape. If the topography is sloping, does a natural drainageway direct surface runoff away from the house, or does the lot need a swale or ridge? If there is an abrupt change in the grading, is there a need for a retaining wall? Are any areas eroding to the extent that corrective action is necessary? Are low or level areas vulnerable to ponding? Ponded water on the lawn does not necessarily indicate a drainage problem. It might be caused by a malfunctioning septic system, a faulty sewer hookup, or a break in the main water-supply pipe. If you find ponded water during your inspection, try to determine the cause.
If there are footing drains around the foundation or curtain drains in a hillside, they will not be visible during your inspection. For these drains to function properly, they must have a free-flowing outlet. (See FIG. 6-9.) Ask the seller if there are drains, and if so, ask for the location of the outlets. Unfortunately, most homeowners do not know whether there are footing or curtain drains. When a house is sold, this type of information is usually not discussed, although it should be. Consequently, the location of the drain outlet is lost for all future owners. If you are lucky enough to have a seller who knows the location of the drain outlet, you should inspect the opening to make sure that it is not obstructed. If the footing drain discharges into a stream channel, an overflowing stream could be a problem. It all depends on the elevation of the footing drain relative to the level when the stream is running full. If the stream is above the level of the footing drain, then water will back up into the drain around the foundation and could cause a water seepage problem. Look for evidence of seepage when inspecting the basement or crawl space. In new homes, the drain outlet is sometimes inadvertently blocked when the lawn is landscaped. If you are buying a new house, ask the builder to show you the location of the drain outlet.