If you plan to build a new home, an addition, or a basement in the San Francisco Bay Area, your project will likely require the services from a geotechnical engineering firm. Geotechnical engineering companies consist of engineers and geologists, who establish site feasibility and design criteria for grading and foundation support. They also have the capacity to evaluate geohazards such as faults and landslides. To develop practical and cost effective foundation options, a geotechnical engineer provides clients and their design teams an understanding of the soil conditions (through soil testing and other methods) and geologic conditions.
The San Francisco Bay Area’s varied geology and seismic conditions demand different building solutions. Closer to the Bay, you may find shallow ground water, expansive soils, and potential for liquefaction settlement. The San Francisco Peninsula hillsides also present building challenges dealing with steep slopes, poor drainage, erosion, poorly placed fills and landslides. Hiring the right geotechnical firm, even when not required by your town, city, or county building department, can be a worthy long-term investment in your home and costs approximately .25% of the total home construction cost.
Flat building sites with expansive clay soils (with shrink-swell properties) can heave with rain and shrink during dry seasons. Expansive clay soils can produce up to 15,000 pounds per square foot of destructive uplift pressure on a foundation. A home built on an inadequate foundation can later show signs of cracks in interior and exterior walls, out of level floors, and doors and windows that stick seasonally. A deeper more rigid conventional foundation may be appropriate for expansive soil sites.
A geotechnical engineer strives to provide practical recommendations, in an effort to avoid over-engineering; this is both a greener and more economical way to proceed with your project. In particular, many areas on the peninsula have superior soils that don’t require massive foundations. On the other hand, portions of San Mateo County are well known for severely expansive claystone that can cause both lateral and vertical movement; in these areas, deep pier foundations may be required to adequately support new residences. The investment in a geotechnical investigation, which produces a soils report, guides the design and construction team to the most appropriate foundation for your specific property.
The geotechnical engineering firm is typically recommended by the architect and hired by the homeowner. The company acts as a homeowner advocate and is involved during the planning and construction phases of your home:
- The geotechnical firm’s scope includes soil borings, laboratory testing, surface and subsurface analysis, and recommendations for a cost-effective foundation. The geotechnical report is used by the architect, civil and structural engineers to prepare the plans and is submitted to the building department.
- The geotechnical engineering company also reviews the project plans and provide a letter to the building department to confirm the plans meet the intentions of the geotechnical report.
- The geotechnical engineer also performs grading and foundation site visits to confirm the project is being built per plan. For example, the geotechnical professional makes sure that foundation footings are properly excavated into the bearing soil or rock before they are ready for concrete placement, or that a demolished swimming pool is properly backfilled with the appropriate non-expansive fill.
To summarize, hiring a geotechnical engineering firm that is familiar with the San Francisco Bay Area is an investment in the long-term performance of your new custom home or home addition. These engineers recommend the most appropriate foundation type and confirm that the grading and foundation installation are being constructed properly.
The photo above is a foundation for a custom home in Los Altos with an interior spread footing that was recommended by Romig Engineers, inc., a geotechnical and geological engineering firm for Peninsula, South Bay and Northern California construction.