BK101 General — 2025 California Residential Code

This appendix provides prescriptive and performance-based requirements for the use of natural cob as a building material. Buildings using cob walls shall comply with this code except as otherwise stated in this appendix.

In addition to the intent described in Section R101.3, the purpose of this appendix is to establish minimum requirements for cob structures that provide flexibility in the application of certain provisions of the code, to permit the use of site-sourced and local materials, and to permit combinations of historical and modern techniques.

Tests for an alternative material, design or method of construction shall be in accordance with Section R104.2.2.5, and the building official shall have the authority to consider evidence of a history of successful use in lieu of testing.

Cob wall systems include those shown in Figure BK101.4 and approved variations.

FIGURE BK101.4—TYPICAL COB WALL

BOND BM

PER SECTION BK106.9

ANCHORS, WHERE OCCUR, PER TABLES BK105.3, BK106.11(1) AND BK106.12

WALL TAPER ALLOWED

ONE OR BOTH SIDES PER SECTION BK106.5(1)

HORIZONTAL REINFORCING, WHERE OCCURS, PER TABLE BK106.11(1)

VERTICAL REINFORCING, WHERE OCCURS, PER TABLE BK106.11(1)

COB MATERIAL

PER SECTION BK103

ANCHORS, WHERE OCCUR, PER TABLE BK106.11(1)

SEPARATION FROM

FINISHED GRADE

PER SECTION BK105.4.4

FINISHED FLOOR LEVEL

VARIES

FINISHED GRADE

FOUNDATION AND STEM WALL

PER SECTION BK106.4

H
HEIGHT,
WALL
COB
F
V