Surface Drainage Adjacent to Houses

One thing we frequently hear from people when buying a new home or when looking for a new home is the concern about proper surface drainage within the first 5-10 feet from a home (backfill zone). This concern is often expressed on both new construction and older homes. The new urban trend of putting homes on smaller lots with more density, yet still having generous home footprints has created some engineering challenges when trying to maintain positive drainage away from a home. As a rule of thumb, about 99% of geotechnical reports and home building guides recommend the following for finished grades outside of a home: 6″ down from top of foundation (TOF) and a minimum of 1′ vertical drop in the first 10′ horizontal (10% slope) (where possible). The key words being “where possible”. As most landscapers, engineers, architects, etc. know it is not always possible to achieve those recommendations given existing constraints. What we try to do as civil engineers when presented with an existing home that has insufficient surface drainage around the building is to look at the entire picture and come up with a long term, low maintenance solution, that is cost effective for the home owner. For example, we first gather accurate survey spot elevations around the entire home and at areas that we anticipate being flow lines for surface drainage away from the house. Our next step is to typically analyze our survey spot elevations and see if we can simply recommend some re-grading adjacent to the home that will help move the surface drainage away from the foundation and into a swale located away from the backfill zone. In many cases, surface drainage adjacent to a home can be drastically improved with some simple (and inexpensive) re-grading adjacent to the home as recommended by a civil engineer. On more complex situations, we look at adding concrete pans and even some basic storm sewer drainage infrastructure such as NDS Drainage Products. Let us know if you are concerned with the drainage adjacent to your home and we’d be happy to schedule a site visit to discuss.