Rainwater and a home's foundation don't make a compatible marriage. Unless its path is diverted, the rain that runs off a roof forms a vertical sheet of water that falls around the perimeter of a house. As the water collects around a home's foundation, the soil can only absorb so much before excess water finds a path of least resistance. To prevent water damage, engineer the rainwater's path to flow away from your house.
A guttering system that you install on your home's roof serves as a perimeter catch basin that collects rainwater. Downspouts channel the collected water from the roof to the ground at the corners of the house and other locations. Guttering systems are effective in moving rainwater away from your house only if you divert the water that comes out of the downspouts. Otherwise, the downspouts deposit the collected rainwater at your home's foundation. Typically, splash blocks that you place underneath the downspouts are too short to move water far enough away from a home's foundation. A better choice is to attach a downspout extender or a flexible corrugated pipe to the downspout terminal that is at least 5 feet long.
Grading the soil away from your house helps carry rainwater away from its foundation. The slope's effectiveness depends on the percentage of the grade and the soil's permeability. As a minimum, the slope should extend 10 feet from the foundation and drop 6 inches, which results in a 5 percent grade. Soils with low permeability, such as clay, typically do not absorb water quickly and are more apt to allow rainwater to flow down a graded slope. Sandy soils that have higher permeability absorb rain water easily. With sandy soil a 10 percent grade is recommended.
Foundation plantings gained popularity around older homes as a way to block the view of their unsightly foundations. This practice is no longer recommended because of how the plants hold water around a home and compromise the integrity of its foundation. Instead, entry gardens are favored as a way to complement a home's design. Remove foundation plantings and replant them -- or replace them with new plants -- beyond the roof's drip line, ideally at least 5 feet from the foundation.
Even if you heed other recommendations for diverting rainwater away from your house, persistent moisture problems may require additional measures to protect the foundation. Drain tile collects rainwater that would otherwise puddle around the foundation and channels it into a sump. The sump is a hole that holds up to 25 gallons of water. Inside the sump is a pump that turns on automatically when the water rises above a certain level. The sump pump moves the water into a pipe, which channels the water away from the house.
- United States Environmental Protection Agency: Technical Guidance to the Indoor airPLUS Construction Specifications
- Rutgers Green Building Manual: New Residential
- International Code Council: National Association of Home Builders RB101
- North Carolina State University Cooperative Extension: Moisture Control and Prevention Guide
- North Dakota State University Extension Service: Sump Pump Helps Keep Water Out
Victoria Lee Blackstone
Victoria Lee Blackstone is a horticulturist and a professional writer who has authored research-based scientific/technical papers, horticultural articles, and magazine and newspaper articles. After studying botany and microbiology at Clemson University, Blackstone was hired as a University of Georgia Master Gardener Coordinator. She is also a former mortgage acquisition specialist for Freddie Mac in Atlanta, GA.