BK108 Fire Resistance — 2025 California Residential Code

BK108.1 Fire-resistance rating.¶

Cob walls that comply with Table BK108.1 have a 2-hour fire-resistance rating.

TABLE BK108.1—TWO-HOUR FIRE-RESISTANCE-RATED COB WALLS

ALLOWABLE SUPER- IMPOSED LOAD (plf)	DENSITYa, d (pcf)	MINIMUM COMPRES- SIVE STRENGTH PER SECTION BK106.6.1 (psi)	WALL-TYPE REINFORCEMENT PER TABLE BK105.3	MINIMUM THICKNESSc, e, f AT TOP OF WALL (inches)	MINIMUM THICKNESSc, e, f AT BOTTOM OF WALL (inches)
1,200	100	85	E	9	12
475	≥ 50 pcf: less than 40 inches from top of wall	40b	E or F	8	12
475	≥ 70 pcf: from 40 inches to 80 inches from top of wall	55b	55b	55b	55b
475	≥ 90 pcf: more than 80 inches from top of wall	85	85	85	85
Nonload bearing	50 to 100	≥ 60 psi < 60 psib	E or F	9	9
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound = 0.45 kg, 1 pound per cubic foot = 16.02 kg/m3. a. Density is to be measured at equilibrium moisture content. Average wall density shall be within ±5 pcf of the tabulated value. b. Requires an approved engineered design per Section BK106.6. c. Cob thickness only. The interior and exterior cob faces shall be permitted to be unfinished or receive any plaster finish allowed by this appendix. d. Cob walls with more than one density shall be built with heavier densities below lighter densities. e. Minimum cob wall thickness shall be whichever is greater in Tables BK105.3, BK106.11(1) and BK108.1. f. Wall thicknesses less than 10 inches require an engineered design.

Exceptions & meaning →

BK108.2 Clearance to fireplaces and chimneys.¶

Cob walls or other cob surfaces shall not require clearance to fireplaces and chimneys, except where clearance to noncombustibles is required by the manufacturer’s instructions.

Exceptions & meaning →