The importance of grading around a home can be demonstrated with some recent failures that I have observed. Landscaping and grading is not just for a beautiful appearance around your home, but is also needed to keep slab-on-grade and crawlspaces dry and prevent structural movement or moisture damage.
As per "Code", something not normally cited, but a good reference point, the grade should slope away from the home at a rate of 1” per foot for the first six feet. This is to encourage any moisture, be it from rain or irrigation sprinklers, to flow away from the structure. When the soil becomes saturated the moisture will migrate downhill. The more moisture that accumulates near the foundation, the more pressure that is put upon the foundation, forcing moisture into the crawlspace or through the slab.
moisture content of wood flooring
I was called to a home in Rancho Santa Fe to investigate a possible moisture issue with a small guesthouse. The homeowner had recently installed wood floors over a concrete slab. Seems that the wood was buckling and warping. When I put my moisture meter on the floor it registered off the scale. A moisture content of 20% and above is conducive to mold growth and moisture damage.
effects of overwatering
After surveying the perimeter of the home, and speaking with the homeowner about their watering habits, it was determined that the homeowner was watering excessively on the slope behind the guesthouse. This was saturating the ground and causing the water to migrate downhill to the guesthouse, where it ultimately ended up in the slab, and the wood floor.
consequences of negative grade
I recommended that the homeowner correct the negative grade issues, water less, and install a french drain on the uphill side of the guesthouse to divert any excess water before it reaches the guesthouse.
Negative grade will have a different effect on a crawlspace. It can manifest itself as efflorescence on the foundation walls. This will eventually weaken the concrete structure or cause movement in the footings.
efflorescence in crawlspace
Or the entire crawl space could become saturated if there is enough moisture. This will lead to water damage and possible microbial growth.
Grading is something that many home owners can overlook, take for granted, or simply underestimate the importance of. As a professional home inspector this is one of the many items that I will be sure my client is aware of. I always recommend that they take the necessary steps to ensure a positive grade away from the home.