Lot grading is extremely important whether your home has a basement, crawlspace or just basic foundations. You want the areas under and adjacent to your home as dry as possible. Water contributes to the degradation of your home’s foundations, basement finishes, the structure of your home and more. There are materials within your home, like concrete and wood that wick water into them, get saturated and even transfer that humidity into other building systems and components.
Ground that diverts surface water (rainwater, melting snow) towards the home may cause extensive damage throughout the home. Correspondingly, when surface water is drained away from the home there are fewer water-related issues in basements and crawlspaces. There is a reduced risk of foundation deterioration due to hydrostatic or frost pressures.
Generally, speaking and minimally, a slope of 15 centimeters per two meters (or one inch per foot for at least six feet) is a common recommendation. That being said, even this recommendation is subject for re-evaluation from site-to-site depending on the soils capacity to absorb water or keep water away from the home and foundations. If the grading around the home includes walkways and driveways, in other words hard, more impervious surfaces, then the recommended slope down and away from the house should be at least 2,54 centimeters per 1,2 meters (one inch per four feet).
Since during an inspection an inspector does not have access to a soil report, and often wet basement conditions are either unknown or concealed by the current owner, the building inspector can only observe both from the outside and inside of the home to validate what may be happening.
Swales are good strategy to deal with difficult lot slopes. Swales (or catch basins) are shallow ditches that in combination with lot sloping away from the home towards the swales, diverts the water away from the home either moving it away from the home, or that retain that water as it percolates into the ground.
The grading around this home sloped slightly towards the home or at best was flat. Visually it was difficult to see that the soil was sloping towards the home, but if you put a long level on the ground it became apparent that the slope was towards the house. In fact, in some places the soil settled over time because it was never compacted and graded properly during the home's construction. It also had down spouts that drained the roof water into drain pipes that were directed down into the soil, not 2 meters (6 feet) away from the home.
The signs that there was water going towards the foundation wall were: the grass up against the home was rotting or having difficulty growing; there were areas where you could see that the soil compacted with time because the painted foundation line was well above the ground-level; there were several cracks along the foundation wall; and, finally, the carpeting in a section of the basement was wet and there were water stains on the baseboard.
Surface water that can migrate towards the foundation of a home can find its way through cracks in the foundation wall and into the home. In freezing cold climates, this water that penetrates the foundation can freeze, expand and further crack the foundation wall. Water infiltrating through a foundation can not only damage interior finishes but it can also damage the structure of the home, promote the growth of mold and mildew, and destroy the foundation.
In conclusion, if there are signs of water migration towards the home and evidence of it in a basement or crawlspace, it cannot be left that way. There are many solutions, some of which may involve a specialized contractor to either waterproof the foundations or regrade and dig swales around the home, or some of this work can become a do-it-yourself project. But do not tolerate this situation.
- Daniel da Chão