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B-41 2020-Current: Residential Pier Foundation Special Inspection

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The purpose of this technical bulletin is to clarify the required inspections for residential pier foundations.

Version: 04/01/2020
Revised: 05/28/2015
Effective date: 02/20/2008

Technical Details

Special inspections are not in lieu of the inspections required by this department, but inaddition to those required inspections. See Technical Bulletin B-14 for general residential special inspection requirements.

Residential Pier Foundations

Based upon the above, residential pier foundations will require special inspection. Inspection procedures for such foundations are as follows:

  1. The soils report will state that a representative of the soils firm shall observe the excavations prior to placing concrete. Verification that this observation has been done and the excavations approved must be on site prior to the foundation inspection by the building inspector.
  2. The building inspector will check that the excavations have been approved by the soils engineer, verify that the special inspector has approved the reinforcement steel, verify the setbacks, reinforcing steel, the number of pier holes, the ufer ground installation, and any other necessary foundation elements.
    1. Pier reinforcing steel may be approved when majority of the steel is in place according to the approved plans, and the rest of the steel is assembled according to the approved plans on site.
    2. If water in piers, collapsing soil, or other similar deficiencies are encountered, the building inspector may require structural observation of the measures taken to correct the deficiencies.
  3. For projects that have been approved for “drill and pour” piers, continuous special inspection is required during the drilling and placement reinforcing steel and concrete. The special inspector shall verify in their report that the placement of reinforcing steel and the number of pier holes were reviewed to the approved plans. Samples and strength tests are required when the required design strength exceeds 2500 psi. “Drill and pour” must be approved in advance by Permit Sonoma Building Division staff.


  • California Building Code, Chapter 17
  • 2019 California Building Code
  • Technical Bulletin B-14