Section AU105

AU105.1 General.¶

Cob walls shall be designed and constructed in accordance with this section and Figure AU101.4 or an approved alternative design. In addition to the general requirements for cob walls in this section, cob structural walls shall comply with Section AU106.

AU105.2 Building limitations and requirements for cob wall construction.¶

wall construction. Cob walls shall be subject to the following limitations and requirements:

Number of stories: not more than one.
Building height: not more than 20 feet (6096 mm).
Seismic design categories: limited to use in Seismic Design Categories A, B and C, except where an approved engineered design is provided.
Wall height: in accordance with Table AU105.3, and with Table AU106.11(1) for braced wall panels.
Wall thickness, excluding finish, shall be not less than 10 inches (254 mm), not greater than 24 inches (610 mm) at the top two-thirds, not limited at the bottom third and, for structural walls, shall comply with Section AU106.2, Item 2. Wall taper is permitted in accordance with Section AU106.5, Item 1.
Interior cob walls shall require an approved engineered design that accounts for the seismic load of the interior cob walls, except in Seismic Design Category A for walls with a height to thickness ratio less than or equal to 6.

AU105.3 Out-of-plane resistance methods and unre-strained wall height limits.¶

strained wall height limits. Cob walls shall employ a method of out-of-plane load resistance in accordance with Table AU105.3, and comply with its associated height limits and requirements.

AU105.3.1 Determination of out-of-plane loading. Outof-plane loading for the use of Table AU105.3 shall be in accordance with the ultimate design wind speed and seismic design category requirements of Sections R301.2.1 and R301.2.2, respectively. An approved engineered design shall be required where the building is located in a special wind region or where wind design is required in accordance with Figure R301.2.1.1.

AU105.3.2 Bond beams for nonstructural walls. Nonstructural cob walls shall be provided with a bond beam at the top of the wall that complies with Section AU106.9, except for requirements relating to roof and/or ceiling loads or braced wall panels.

AU105.3.3 Lintels in nonstructural walls. Door, window and other openings in nonstructural cob walls shall require a lintel in accordance with Section AU106.10, except for requirements relating to roof and/or ceiling loads or braced wall panels.

AU105.3.4 Reinforcing at wall openings. Reinforcing shall be installed at window, door, and similar wall openings and penetrations greater than 2 feet (610 mm) in width in accordance with Sections AU105.3.4.1 through AU105.3.4.3. Surface voids deeper than 25 percent of the wall thickness shall be considered an opening.

AU105.3.4.1 Opening size limit. Openings shall not exceed 6 feet (1829 mm) in width, and the height of the cob wall below openings shall not exceed 6 feet (1829 mm) above the top of the foundation.

AU105.3.4.2 Horizontal reinforcing. Two-inch by 2inch (51 mm by 51 mm) 14-gage galvanized steel mesh shall be embedded 4 inches (102 mm) in the cob above the rough opening and below the rough opening for windows, and shall extend 12 inches (305 mm) beyond the sides of the opening. Walls below rough window openings greater than 4 feet 6 inches (1372 mm) in height shall be provided with additional horizontal reinforcing at midheight.

AU105.3.4.3 Vertical reinforcing. Full-height ⁵ /8-inch (16 mm) threaded rod shall be installed 4 inches (102

APPENDIX AU-4 2022 CALIFORNIA RESIDENTIAL CODE

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mm) from each side of the opening, centered in the thickness of the cob wall. The threaded rods shall be embedded 7 inches (178 mm) in the foundation, and 4 inches (102 mm) in concrete bond beams or shall penetrate through wood bond beams and be secured with a nut and washer. The threaded rods shall be embedded in concrete lintels or pass through a drilled hole in wood lintels.

AU105.3.5 Minimum length of cob walls. Sections of cob walls between openings shall be not less than 2 feet, 6 inches (762 mm) in length. Wall sections less than 4 feet (1219 mm) and not less than 2 feet, 6 inches (762 mm) in length shall contain vertical reinforcing in accordance with Section AU105.3.4.3.

AU105.4 Moisture control.¶

Cob walls shall be protected from moisture intrusion and damage in accordance with Sections AU105.4.1 through AU105.4.5.

APPENDIX AU—COB CONSTRUCTION (MONOLITHIC ADOBE)

AU105.4.1 Water-resistant barriers and vapor perme- ance. Cob walls shall be constructed without a membrane barrier between the cob wall and plaster to facilitate transpiration of water vapor from the wall, and to secure a mechanical bond between the cob and plaster, except as otherwise required elsewhere in this appendix. Where a water-resistant barrier is placed behind an exterior finish, it shall be considered part of the finish system and shall comply with Item 2 of Section AU104.1.2 for the combined vapor permeance rating.

AU105.4.2 Horizontal surfaces. Cob walls and other cob elements shall be provided with a water-resistant barrier at weather-exposed horizontal surfaces. The water-resistant barrier shall be of a material and installation that will prevent erosion and prevent water from entering the wall system. Horizontal surfaces, including exterior window sills, sills at exterior niches and exterior buttresses, shall be sloped not less than 1 unit vertical in 12 units horizontal to drain away from cob walls or other cob elements.

TABLE AU105.3 OUT-OF-PLANE RESISTANCE METHODS AND UNRESTRAINED WALL HEIGHT LIMITS

WALL TYPEa, g, h AND METHOD OF OUT-OF-PLANE LOAD RESISTANCE	FOR ULTIMATE DESIGN WIND SPEEDS (mph)	FOR SEISMIC DESIGN CATEGORIES	UNRESTRAINED COB WALL HEIGHT Hb, c, h		TOP ANCHORe SPACING (inches)	TENSION TIEf SPACING (inches)
WALL TYPEa, g, h AND METHOD OF OUT-OF-PLANE LOAD RESISTANCE	FOR ULTIMATE DESIGN WIND SPEEDS (mph)	FOR SEISMIC DESIGN CATEGORIES	Absolute Limit (feet)	Limit Based on Wall Thickness_T_d (feet)	Limit Based on Wall Thickness_T_d (feet)	Limit Based on Wall Thickness_T_d (feet)
Wall 1i: no anchors, no steel wall reinforcing	≤ 110	A	H ≤ 8	H ≤ 6_T_	None	48
Wall 2: top anchorsj, continuous vertical 6″ × 6″ × 6″ gage steel mesh in center of wall embedded in founda- tion 12 inches	≤ 140	A, B, C	H ≤ 8	H ≤ 8_T_	12	24
Wall Ai: top anchors, no vertical steel reinforcing	≤ 120	A, B	H ≤ 8	H ≤ 6_T_	12	48
Wall Bi: top and bottom anchors, no vertical steel rein- forcing	≤ 130	A, B	H ≤ 8	H ≤ 6_T_	12	48
Wall C: top and bottom anchors, continuous vertical threaded rod at 4 feet on center embedded in founda- tion and connected to bond beam	≤ 140	A, B, C	H ≤ 8	H ≤ 8_T_	12	24
Wall D: continuous vertical threaded rod at 1 foot on center embedded in foundation and connected to bond beam	≤ 140	A, B, C	H ≤ 8	H ≤ 8_T_	N/A	24
Wall E: top anchors, continuous vertical 6″ × 6″ × 6″ gage steel mesh 2 inches from each face of wall embedded in foundation	≤ 140	A, B, C	H ≤ 8	H ≤ 8_T_	12	24

For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 mile per hour = 0.447 m/s.

N/A = Not Applicable a. See Table AU106.11(1) for reinforcing and anchorage specifications for wall Types A, B, C, D and E. b. H = height of the cob portion of the wall only. See Figure AU101.4. The maximum H is the absolute limit or the limit based on wall thickness, whichever is

more restrictive. c. Bond beams or other horizontal restraints are capable of separating a wall into more than one unrestrained wall height with an approved engineered design. d. T = Cob wall thickness (in feet) at its minimum, without plaster. e. ⁵ /8-inch threaded rod anchors at prescribed spacing with 12-inch embedment in cob, full embedment in concrete bond beams or full penetration in wood bond

beam with a nut and washer. f. Attach rafters to bond beam with 4-inch by 3-inch by 3-inch by 18 gage tension tie angles at prescribed spacing. See Figure AU106.9.5. Where rafters are

attached to tension ties, roof sheathing shall be edge nailed. g. All walls shall be tested for compressive strength in accordance with Section AU106.6. h. For curved walls with an arc length to radius ratio of 1.5:1 or greater, the H / T factor shall be increased by 1, and the absolute height limit by 1 foot. i. Wall type requires a modulus of rupture test in accordance with Section AU106.7. j. See wall Type A in Table AU106.11(1) for top anchor requirements.

APPENDIX AU—COB CONSTRUCTION (MONOLITHIC ADOBE)

AU105.4.3 Separation of cob and foundation. A liquidapplied or bituminous Class II vapor retarder shall be installed between cob and supporting concrete or masonry.

Exception: Where local climate, site conditions and foundation design limit ground moisture migration into the base of the cob wall, including but not limited to the use of a moisture barrier or capillary break between the supporting concrete or masonry and the earth.

AU105.4.4 Separation of cob and finished grade. Cob shall be not less than 8 inches (203 mm) above finished grade.

Exception: The minimum separation shall be 4 inches (102 mm) in dry climate zones as defined in Section N1101.7.2, and shall be 2 inches (51mm) on walls that are not weather exposed.

AU105.4.5 Installation of windows and doors. Windows and doors shall be installed in accordance with the manufacturer’s instructions to a wooden frame of not less than nominal 2-inch by 4-inch (51 mm by 102 mm) wood members anchored into the cob wall with 16d galvanized nails half-driven at a maximum 6-inch (152 mm) spacing, with the protruding half embedded in the cob. The wood frame shall be embedded not less than 1 ¹ /2 inches (38 mm) in the cob and shall be set in from each face of the wall not less than 3 inches (76 mm). Alternative window and door installation methods shall be capable of resisting the wind loads in Table R301.2.1(1). Windows and doors in cob walls shall be installed so as to mitigate the passage of air or moisture into or through the wall system. Window sills shall comply with Section AU105.4.2.

AU105.5 Inspections.¶

In addition to ensuring compliance with Section R109.1, the building official shall inspect the following aspects of cob construction:

Anchors and vertical and horizontal reinforcing in cob walls, where required in accordance with Tables AU105.3 and AU106.11(1) and Sections AU105.3.4 through AU105.3.5.
Reinforcing in any concrete bond beams or lintels, in accordance with Section AU106.9.2 and Table AU106.10.