An experienced builder understands that a sloped building lot presents issues such as stability, varying soil types, possible erosion, and poor drainage which can complicate construction and drive up costs.
The slope of the site might be obvious. If site drops six feet from one end to the other, for instance, you know you may need a deeper foundation on the low side, or a stepped-down foundation. Soil types are less obvious, but unstable soils can require remediation that also makes a site challenging to build on. And we have written previously about the utility of trenching to control water flow.
Excavating on Sloping Terrain
A slight slope actually adds a nice aesthetic aspect to a building, so we often work with the engineer to maintain it rather than excavate it. A low slope also facilitates site drainage, keeping the foundation clear of water. A grade of 10% or less presents few challenges when drilling and excavating to prepare a site for foundation construction.
Moderate slopes, with a 15% to 20% rise, require more care when grading (and when maneuvering our drilling and excavating equipment!) We may be excavating space for a stepped-down foundation with a walk-out basement, for instance.
Steep slopes. When the grade rises above 20%, we may need to carry out more extensive earth moving and soil stabilization to create a workable worksite and prevent erosion. We might also have to truck in additional fill to build up an area of slope.
Erosion during the building process must be controlled. Regrading eroded areas can add to a project’s final cost, and we work to avoid it. Terracing, soil stabilization techniques, retaining walls, and special foundation and drainage techniques may be needed to ensure a sound foundation on which to build.
Hillside foundations. Houses are routinely built on extreme grades of 50% or more in Northern California. Hillside home sites are popular given the views they offer. This type of construction demands highly engineered foundations installed by specialists in hillside work. In our 30 years of Bay Area foundation work, we have built that specialized skill set.
Drainage of steep slopes. On steep sites, we have to account for the site-specific soils and drainage patterns. If we find dense soils on the uphill side of a foundation that hold water well, winter rains can create soil conditions that exert extra force on the foundation wall facing the slope. Conversely, if the soil doesn’t hold the water, fast runoff can cause excessive erosion if not channeled properly using French Drains and other techniques. Input from a civil or geotechnical engineer familiar with local conditions makes all the difference!
Very steep sites may also require specially engineered piping and leach fields, which we need to incorporate into our excavating, drilling and trenching plans.
Call the Pros When a Highly Sloped Building Site Needs Excavation
We have been excavating Bay Area construction sites of all grades for thirty years. If you need more information about our services, or a referral to a civil engineer who can help assess your site and draw up a sound construction plan, contact us!