Chapter 44 — REFERENCED STANDARDS
Section BK106 — COB WALLS—STRUCTURAL
2025 California Residential Code (Title 24, Part 2.5) · 2025 edition · ingested 2026-07-07 · California
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BK106.1 General. ¶
BK106.1 General. Cob structural walls shall be in accordance with the prescriptive provisions of this section. Designs or portions of designs not complying with this section shall require an approved design by a registered design professional, except where an engineered design is required.
BK106.2 Requirements for cob structural walls. ¶
BK106.2 Requirements for cob structural walls. In addition to the requirements of Section BK105.2, cob structural walls shall be subject to the following: 1. Wall height: shall be in accordance with Table BK105.3 for load-bearing cob walls or Table BK106.11(1) for cob braced wall panels, as applicable and most restrictive. 2. Wall thickness: shall be in accordance with Sections BK105.2, Item 5 and Section BK106.8.1 for load-bearing cob walls or Table BK106.11(1) for cob braced wall panels, as applicable and most restrictive. 3. Braced wall panel lengths: for buildings using cob braced wall…
BK106.3 Loads and other limitations. ¶
BK106.3 Loads and other limitations. Live and dead loads and other limitations shall be in accordance with Section R301, except that the dead load for cob walls shall be determined by Equation BK-1. Equation BK-1 CW DL = ( H × T avg × D ) CW DL = Cob wall dead load (in pounds per lineal foot of wall). H = Height of cob portion of wall (in feet). T avg = Average thickness of wall (in feet). D = Density of cob = 110 (in pounds per cubic foot), unless a lesser value at equilibrium moisture content is demonstrated to the building official.
BK106.4 Foundations. ¶
BK106.4 Foundations. Foundations for cob walls shall be in accordance with Chapter 4. The width of foundations for cob walls shall be not less than the width of the cob at its base, excluding finish.
BK106.5 Wall taper, straightness and surface voids for cob walls. ¶
BK106.5 Wall taper, straightness and surface voids for cob walls. Cob walls shall be in accordance with the following: 1. Cob structural and nonstructural walls shall be vertical or shall taper from bottom to top with the wall thickness in accordance with Section BK105.2, Item 5 and the wall height in accordance with Section BK105.2, Item 4. APPENDIX BK-8 2025 CALIFORNIA RESIDENTIAL CODE on Jul 18, 2025 11:14 AM (CDT) THEREUNDER. APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE) 2. Cob structural and nonstructural walls shall be straight or curved. Curved braced wall panels shall be in…
BK106.6 Compressive strength of cob structural and nonstructural walls. ¶
BK106.6 Compressive strength of cob structural and nonstructural walls. All cob walls shall have a minimum compressive strength of 60 psi (414 kPa), and cob in walls used as braced wall panels shall have a minimum compressive strength of 85 psi (586 kPa), except with an approved engineered design. BK106.6.1 Demonstration of compressive strength. The compressive strength of the cob mix to be used in structural walls and nonstructural walls as required in Section BK106.6 shall be demonstrated to the building official before the placement of cob onto walls, with compressive strength tests and an…
BK106.7 Modulus of rupture of cob structural walls. ¶
BK106.7 Modulus of rupture of cob structural walls. Cob in walls used as braced wall panels shall have a minimum modulus of rupture of 50 pounds per square inch (345 kPa). BK106.7.1 Demonstration of modulus of rupture. The modulus of rupture of cob used in structural walls shall be demonstrated to the building official before the placement of cob onto walls, with modulus of rupture tests and an associated report by an approved laboratory or with an approved on-site test as follows: 1. Five samples of the proposed cob mix shall be placed moist to completely fill a 6-inch by 6-inch by 12-inch…
BK106.8 Bearing capacity. ¶
BK106.8 Bearing capacity. The allowable bearing capacity for cob load-bearing walls supporting vertical roof and/or ceiling loads imposed in accordance with Section R301 shall not exceed 2,200 pounds per linear foot (plf) and shall be determined by Equation BK2. Use of bearing capacities determined with Equation BK-2 exceeding 2,200 plf requires an approved design prepared by a registered design professional that accounts for buckling. Equation BK-2 BC = ( C × T min × 12)/3 – ( H × T avg /12 × D ) BC = Allowable bearing capacity of wall (in pounds per lineal foot of wall). C = Compressive…
BK106.9 Bond beams. ¶
BK106.9 Bond beams. Cob structural walls shall require a bond beam at the top of the wall in accordance with Section BK106.9.1, BK106.9.2 or BK106.9.3, and shall be anchored to the cob below in accordance with Tables BK105.3, BK106.11(1) and BK106.12, as applicable and most restrictive. Bond beams spanning openings shall be in accordance with Section BK106.9.4. BK106.9.1 Wood bond beams. Wood bond beams shall be not less than nominal 4 inches (102 mm) high by 8 inches (203 mm) wide and shall comply with Sections BK106.9.1.1 through BK106.9.1.3. on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.…
BK106.10 Lintels. ¶
BK106.10 Lintels. Door, window and other openings in load-bearing cob walls shall be provided with a lintel of wood or concrete in accordance with Table BK106.10. TABLE BK106.10—LINTELS AND BOND BEAMS SPANNING OPENINGSCol2Col3Col4Col5Col6Col7 --------------------- GROUND SNOW LOAD ≤ 30 PSFGROUND SNOW LOAD ≤ 30 PSFGROUND SNOW LOAD ≤ 30 PSFWOOD: <br•<brFb ≥ 850 psi<br•<brE ≥ 1,300,000 psi<br•<brNo. 2 Grade or better<br•<brOriented flat<br•<br1 piece or 2 equal-width pieces<br•<brExtend 1 foot beyond opening sidesWOOD: <br•<brFb ≥ 850 psi<br•<brE ≥ 1,300,000 psi<br•<brNo.
BK106.11 Cob braced wall panels. ¶
BK106.11 Cob braced wall panels. Cob braced wall panels shall be in accordance with Section R602.10 and Tables BK106.11(1), BK106.11(2), BK106.11(3), BK106.11(4) and BK106.11(5). Wind design criteria shall be in accordance with Section R301.2.1. Seismic design criteria shall be in accordance with Section R301.2.2. An approved engineered design shall be required in accordance with Section R301.2.1 where the building is located in a special wind region or where wind design is required in accordance with Figure R301.2.1.1. TABLE BK106.11(1)—COB BRACED WALL PANEL TYPESCol2Col3Col4Col5Col6Col7…
BK106.12 Resistance to wind uplift forces. ¶
BK106.12 Resistance to wind uplift forces. Cob walls that resist uplift forces from the roof assembly, as determined in accordance with Section R802.11, shall be in accordance with Table BK106.12. TABLE BK106.12—ANCHORAGE OF BOND BEAMS FOR WIND UPLIFTCol2Col3Col4 ------------ ANCHORS: <br•<br5/8″ ALL THREAD AT 12″ O.C.a, b<br•<br2″ × 2″ ×1/4″ WASHERS AND NUT AT END IN COB<br•<br4″ EMBEDMENT IN CONCRETE BOND BEAMS<br•<brFULL PENETRATION THROUGH WOOD BOND BEAMS WITH 2″ × 2″ ×1/4″ WASHER AND NUTANCHORS: <br•<br5/8″ ALL THREAD AT 12″ O.C.a, b<br•<br2″ × 2″ ×1/4″ WASHERS AND NUT AT END IN…
BK106.13 Post-and-beam with cob infill. ¶
BK106.13 Post-and-beam with cob infill. Post-and-beam with cob infill wall systems shall be in accordance with an approved engineered design.
BK106.14 Buttresses. ¶
BK106.14 Buttresses. Cob buttresses that are intended to provide out-of-plane wall bracing or additional capacity for braced wall panels shall be in accordance with an approved engineered design. on Jul 18, 2025 11:14 AM (CDT) THEREUNDER. APPENDIX BK — COB CONSTRUCTION (MONOLITHIC ADOBE)