According to California regulations, when is a soils investigation report required for new residential construction?
Correct Answer
A) For all construction in Seismic Design Categories D, E, and F
CBC Section 1803.5.12 mandates that a geotechnical investigation be conducted for structures assigned to Seismic Design Category D, E, or F. Given California's high seismicity, most areas fall into these categories, making soils reports a standard requirement for new construction.
Why This Is the Correct Answer
California Building Code Section 1803.5.12 specifically mandates geotechnical investigations for all structures assigned to Seismic Design Categories D, E, and F. Since California is located in a highly seismic region, the vast majority of the state falls into these high-risk seismic categories. This makes soils investigation reports a standard requirement for virtually all new residential construction projects throughout California, regardless of building height, slope conditions, or building official discretion.
Why the Other Options Are Wrong
Option B: Only for structures over 3 stories in height
Building height is not the determining factor for soils investigation requirements. The CBC requires geotechnical reports based on seismic design category, not the number of stories. Even single-story homes in high seismic zones (Categories D, E, F) require soils reports, while tall buildings in lower seismic zones might not need them under this specific provision.
Option C: When the structure is located on a slope greater than 20%
While steep slopes can trigger additional geotechnical requirements under other code sections, the 20% slope threshold is not the primary trigger for mandatory soils investigations. The seismic design category is the controlling factor under CBC Section 1803.5.12, meaning even flat sites in high seismic zones require geotechnical reports.
Option D: Only when the building official determines the site has questionable soil conditions
This option makes the requirement discretionary rather than mandatory. CBC Section 1803.5.12 establishes clear, objective criteria based on seismic design categories, not subjective building official judgment. While building officials have authority in many areas, soils investigations for high seismic zones are required by code, not left to individual determination.
Memory Technique
Remember 'DEF needs dirt' - Seismic Design Categories D, E, and F DEFinitely need geotechnical investigation of the dirt (soil) before construction can begin.
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