B-14 2020-Current: Residential Special Inspection and Structural Observation

The purpose of this technical bulletin is to clarify the requirements for special inspections and structural observations based on Chapter 17 of the 2019 California Building Code (CBC) for the construction/alteration of one or two-family dwellings of Group R-3 occupancies and residential accessory U occupancies.  Chapter 17 specifies when special inspections or structural observations are required or exempt based on building and/or site characteristics (e.g. height, geometry, construction materials, type of construction, wind/seismic loading, foundation type, etc.).  Chapter 17 also allows the building official to require special inspection and structural observation when requested by the building official.  This bulletin provides general guidelines of the instances when Permit Sonoma will require special inspection and structural observation.

Special inspections and structural observations are not in lieu of the inspections required by this department, but in addition to those required inspections (CBC 1704.2).  Where special inspection or structural observation is required below, they shall be conducted per the requirements of Chapter 17.

Effective Date: 01/2019
Revised: 07/27/2021
Revised: 02/20/2008
Revised: 05/28/2015
Revised: 12/16/2016
Revised: 02/13/2017

Group R-3 Special Inspection Requirements

• CBC Sections 1705.2 through 1705.10 describe special inspection for various materials and construction methods:  Steel, Concrete, Masonry; Wood, Soils, Driven Deep Foundations, Cast-in-place Deep Foundations, and Helical Pile Foundations.  (Sonoma County does not have wind loads that would require special inspection for wind resistance per CBC 1705.11)  Based upon these sections, special inspections are generally required for R-3 Occupancies whenever a construction material or method listed in those sections is proposed.
• CBC 1705.12 Special Inspections for seismic resistance exempts special inspection for detached one or two-family dwellings except those that exceed two stories above grade plane, provided the structure does not have any of the following horizontal or vertical irregularities in accordance with Section 12.3.2 of ASCE 7:
  1. Torsional irregularity
  2. Nonparallel systems
  3. Stiffness irregularity—extreme soft story and soft story
  4. Discontinuity in capacity—weak story
  If the irregularities above are not present in the design then inspection requirements of CBC 1705.12.1 through 1705.12.9 do not apply with the exception of 1705.12.1 for Structural Steel and 1705.12.9 for Cold-formed steel special bolted moment frames.  The requirements of CBC 1705.1 through 1705.10 would still apply.  Inspection is required for moment frame anchorage.
• Special Inspection is also required if:
  1. The registered design professional who prepares the plans states that special inspection is required or recommended.
  2. Items where the product listing specifically requires special inspection, such as epoxy anchors.
  3. Other cases when specifically required by the building official and/or his or her designee.

Group U Special Inspection Requirements

• CBC Section 1704.2 exempts special inspection for U occupancies that are accessory to residential occupancies unless otherwise required by the building official. Special inspection requirements for U-Occupancy Structures will be the same as listed above for R-3 Occupancies. The exemption noted in section 1704.2 will only apply to agricultural exempt structures.

Structural Observations

• Structural observation is typically performed by the design professional in responsible charge, although it can be performed by another registered professional if the registered design professional in responsible charge is not available and has pre-approved a substitute.

  • Areas of Sonoma County are either located in Seismic Design Category (SDC) D or E. CBC Section 1704.6.1 and 1704.6.2 requires structural observation in SDC C, D, E, & F for the following cases:
    1. Such observation is required by the registered design professional responsible for the structural design.
    2. The structure is greater than two stories above grade plane and in SDC E, and classified as either Risk Category I or II. (R-3 and residential accessory U occupancies would be classified as either Risk Category I or II.)
  • Per CBC 1704.6.1 structural observations for structures also must be performed when specifically required by the building official. These cases may include but are not limited to:
    1. Permits to resolve code enforcement violations.
       • Prior to plancheck approval, the engineer of record shall submit the verification methodology per Concealed Construction Verification Guidelines, Policy and Procedure 1-4-2 and a written statement identifying the frequency and extent of structural observations (1704.6).
    2. Wood Frame structures with any of the following:
       • Greater than 5000 square feet
       • Two story structures with upper shear walls not located directly above lower level shear walls.
       • Drag connections
       • Shear walls with staggered edge nailing at 3 inches on center or less
    3. Horizontal or Vertical Irregularities per ASCE7-10 Sections 12.3.2.1 and 12.3.2.2.
    4. Diaphragms with construction other than unblocked wood sheathed diaphragms with maximum 6 inches edge or boundary nailing.
    5. Foundations that support lateral load resisting systems other than wood shear walls

  References

  • 2019 California Building Code (CBC) Chapter 17
  • 2019 California Building Code (CBC) Chapter 23
  • 2019 California Residential Code (CRC) Chapter 3 & 4
  • American Society of Civil Engineers (ASCE) 7-16