CHBC · California Historical Building Code
What are general CHBC requirements for adobe and moisture protection?
Under the CHBC, adobe must be protected from moisture and kept in reasonably good condition (see **§ 8-806.1** and **§ 8-806.2**). The code is performance-based: it requires provisions and evaluation for moisture-related deterioration but does not list numeric moisture limits in these sections — those numeric test limits are found in the regular CBC and referenced standards. For repairs, use compatible materials, document condition, and get the enforcing agency’s concurrence for alternative approaches.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
The California Historical Building Code requires that unburned clay masonry (adobe) be managed so it does not deteriorate from water — in other words, provisions to protect adobe from moisture penetration must be in place and adobe must be maintained in reasonably good condition. This is stated in § 8-806 and specifically in § 8-806.1 (scope/alternative approaches) and § 8-806.2 (moisture protection) of the CHBC.
Protect adobe from moisture: the CHBC requires measures to prevent deterioration from moisture and that adobe walls be maintained in reasonably good condition.
Requirements in detail
Key plain-language obligations (CHBC)
- Scope — § 8-806.1: Unburned clay masonry (adobe) may be constructed, reconstructed, stabilized or rehabilitated under the CHBC; alternative approaches that provide equivalent or greater safety are allowed with the enforcing agency’s concurrence.
- Moisture protection — § 8-806.2: Provisions shall be in place to protect adobe structures from deterioration due to moisture penetration. Particular attention must be paid to the moisture content of adobe walls; unmaintained walls or ruins must be evaluated for safety and additional protection measures may be required with the enforcing agency’s concurrence.
Decision-relevant dimensions / values (CHBC text)
| Decision point | What the CHBC requires | Why it matters | Code Reference |
|---|---|---|---|
| What material is covered | Unburned clay masonry (adobe) may be handled under this chapter | Identifies applicability of the CHBC Adobe rules | § 8-806.1 |
| Primary moisture rule | Provisions to protect adobe from moisture penetration must be in place | Water accelerates loss of strength and deterioration of adobe units | § 8-806.2 |
| Maintenance expectation | Adobe shall be maintained in reasonably good condition | Ongoing maintenance prevents progressive deterioration | § 8-806.2 |
| Unmaintained walls / ruins | Evaluate for safety based on condition and stability; extra protection may be required | Unsafe ruins may need shoring, stabilization, reconstruction or demolition | § 8-806.2 |
| Use of alternatives | Alternative approaches (that give equal/greater safety) may be used with enforcing agency concurrence | Allows tailored repairs that respect historic fabric while ensuring safety | § 8-806.1 |
Notes: The CHBC language is performance/condition-based rather than prescriptive for moisture (it does not set a numeric moisture limit in § 8-806.2). For numerical test criteria applied to adobe units (e.g., unit moisture-content limits or laboratory requirements), other codes such as the California Building Code (CBC) contain specific numeric limits — see Related Provisions below.
Short checklist for plan reviewers / contractors (from CHBC)
- Confirm the work involves adobe as defined in the chapter and that CHBC procedures apply. § 8-806.1
- Verify that the project includes measures to prevent moisture penetration (e.g., drainage, capillary breaks, protective finishes, waterproofing where historically appropriate) — CHBC requires provisions but allows flexibility with enforcing agency concurrence. § 8-806.2
- Require an inspection/report for unmaintained walls or ruins before reuse or occupancy; document condition and proposed protection measures. § 8-806.2
Exceptions & special cases
- Alternative methods that provide an equal or greater level of safety are permitted, but they require the concurrence of the enforcing agency (i.e., your building official). § 8-806.1
- Unmaintained walls or ruins are not treated the same as intact, maintained adobe — they must be evaluated for safety and may require additional protection measures beyond routine maintenance. § 8-806.2
- The CHBC language is intentionally flexible (performance-based). It does not itself list required materials or exact protective details (e.g., it does not specify exact waterproofing products or moisture content thresholds in § 8-806.2). For prescriptive or numeric specifications, the project may need to refer to the regular CBC or conduct testing as part of the structural survey/agreed approach.
Common mistakes
- Assuming § 8-806.2 gives a numeric moisture limit. It does not — CHBC requires attention to moisture but is non‑prescriptive; numeric limits are found in other codes (see Related Provisions).
- Failing to get the enforcing agency’s concurrence for an alternate protective approach or for nonstandard repair techniques — CHBC explicitly requires concurrence for alternatives. § 8-806.1
- Treating ruins or visibly deteriorated adobe the same as sound, maintained walls — CHBC requires evaluation and possibly extra protection or stabilization for unmaintained walls. § 8-806.2
- Overlooking compatibility of repair materials with original adobe (CHBC permits traditional compatible materials; see related adobe repair sections in CHBC).
Worked example — applying the CHBC requirement
Scenario: An inspector finds a one-story historic adobe wall with visible softening near the base after seasonal flooding. Laboratory moisture measurement of a sampled adobe unit reads 6% moisture by weight.
Step 1 — CHBC obligation: Under § 8-806.2, provisions must be in place to protect the wall from moisture penetration and the wall must be maintained in reasonably good condition; because the wall shows deterioration and elevated moisture, it needs evaluation and protective measures.
Step 2 — Evaluate severity: The CHBC does not give a numeric “pass/fail” moisture threshold in § 8-806.2, so document condition, test for strength/deterioration, and develop a protection plan. Note: the CBC (regular code) sets a moisture-content limit for adobe units at 4% by weight for some adobe unit tests, which can be used as a technical reference when determining acceptability or repair scope. If measured moisture is 6%, it exceeds the CBC test threshold and supports the finding that the unit is at risk and that additional protection/stabilization is warranted.
Step 3 — Action & approval: Propose measures (e.g., improved drainage away from the wall, repair of protective plaster/roof overhangs, replacement of saturated lower-course units with stabilized adobe compatible with the original, and/or temporary shoring). Submit the approach to the enforcing agency; because CHBC allows alternative approaches with concurrence, obtain written concurrence before major nonstandard repairs. § 8-806.1, § 8-806.2
Related provisions (quick list)
- § 8-806.3 — Height-to-thickness ratio limits for unreinforced adobe walls (addresses when out-of-plane evaluation is needed).
- § 8-806.4 — Nonload-bearing adobe: evaluation and anchorage against out-of-plane failure.
- § 8-806.5 — Bond beam requirements where provided (top-of-wall structural element).
- § 8-806.6 — Repair or reconstruction: allows use of unstabilized brick or adobe compatible with existing materials.
- § 8-806.7 — Allowable shear values for existing adobe (strength considerations).
- For numeric unit test criteria (e.g., moisture content limits such as 4%), see the California Building Code provisions on adobe (for example CBC § 2109.2.1.3), which supply laboratory test limits used in engineered evaluations; CHBC § 8-806.2 directs attention to moisture but is not prescriptive for numeric test values.
Code references
Grounded in the retrieved California Historical Building Code — click a citation to read the verbatim passage:
CHBC § 2109.2.1.2 High relevance — show source text
2109.2.1.2 Modulus of rupture. Adobe units shall have an average modulus of rupture of 50 psi (345 kPa) when tested in accordance with the following procedure. Five samples shall be tested and individual units shall not have a modulus of rupture of less than 35 psi (241 kPa).
2109.2.1.2.1 Support conditions. A cured unit shall be simply supported by 2-inch-diameter (51 mm) cylindrical supports located 2 inches (51 mm) in from each end and extending the full width of the unit.
2109.2.1.2.2 Loading conditions. A 2-inch-diameter (51 mm) cylinder shall be placed at midspan parallel to the supports.
2109.2.1.2.3 Testing procedure. A vertical load shall be applied to the cylinder at the rate of 500 pounds per minute (37 N/s) until failure occurs.
2109.2.1.2.4 Modulus of rupture determination. The modulus of rupture shall be determined by the equation: Equation 21-2 f r = 3 PL s /[2 S w ( S t 2 )]
2109.2.1.3 Moisture content requirements. Adobe units shall have a moisture content not exceeding 4 percent by weight.
2109.2.1.4 Shrinkage cracks. Adobe units shall not contain more than three shrinkage cracks and any single shrinkage crack shall not exceed 3 inches (76 mm) in length or [1] / 8 inch (3.2 mm) in width.
2109.2.2 Stabilized adobe. Stabilized adobe shall comply with Section 2109.2.1 for unstabilized adobe in addition to Sections 2109.2.2.1 and 2109.2.2.2.
2109.2.2.1 Soil requirements. Soil used for stabilized adobe units shall be chemically compatible with the stabilizing material.
2109.2.2.2 Absorption requirements. A 4-inch (102 mm) cube, cut from a stabilized adobe unit dried to a constant weight in a ventilated oven at 212°F to 239°F (100°C to 115°C), shall not absorb more than 2 [1] / 2 percent moisture by weight when placed on a constantly water-saturated, porous surface for seven days. Not fewer than five specimens shall be tested and each specimen shall be cut from a separate unit.
2109.2.3 Allowable stress. The allowable compressive stress based on gross cross-sectional area of adobe shall not exceed 30 psi (207 kPa).
2109.2.3.1 Bolts. Bolt values shall not exceed those set forth in Table 2109.2.3.1.
CHBC § 2109.2.1.3 High relevance — show source text
2109.2.1.3 Moisture content requirements. Adobe units shall have a moisture content not exceeding 4 percent by weight.
2109.2.1.4 Shrinkage cracks. Adobe units shall not contain more than three shrinkage cracks and any single shrinkage crack shall not exceed 3 inches (76 mm) in length or [1] / 8 inch (3.2 mm) in width.
2109.2.2 Stabilized adobe. Stabilized adobe shall comply with Section 2109.2.1 for unstabilized adobe in addition to Sections 2109.2.2.1 and 2109.2.2.2.
2109.2.2.1 Soil requirements. Soil used for stabilized adobe units shall be chemically compatible with the stabilizing material.
2109.2.2.2 Absorption requirements. A 4-inch (102 mm) cube, cut from a stabilized adobe unit dried to a constant weight in a ventilated oven at 212°F to 239°F (100°C to 115°C), shall not absorb more than 2 [1] / 2 percent moisture by weight when placed on a constantly water-saturated, porous surface for seven days. Not fewer than five specimens shall be tested and each specimen shall be cut from a separate unit.
2109.2.3 Allowable stress. The allowable compressive stress based on gross cross-sectional area of adobe shall not exceed 30 psi (207 kPa).
2109.2.3.1 Bolts. Bolt values shall not exceed those set forth in Table 2109.2.3.1.
TABLE 2109.2.3.1—ALLOWABLE SHEAR ON BOLTS IN ADOBE MASONRY Col2 Col3 DIAMETER OF BOLTS (inches) MINIMUM EMBEDMENT (inches) SHEAR (pounds) 1/2 — — 5/8 12 200 3/4 15 300 7/8 18 400 1 21 500 11/8 24 600 For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. 2109.2.4 Detailed requirements. Adobe construction shall comply with Sections 2109.2.4.1 through 2109.2.4.9.
2109.2.4.1 Number of stories. Adobe construction shall be limited to buildings not exceeding one story, except that two-story construction is allowed where designed by a registered design professional.
2025 CALIFORNIA BUILDING CODE 21-9
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
2109.2.4.2 Mortar. Mortar for adobe construction shall comply with Sections 2109.2.4.2.1 and 2109.2.4.2.2.
CHBC § 8-805.3 High relevance — show source text
8-805.3 Reconstructed walls. Totally reconstructed walls utilizing original brick or masonry, constructed similar to original, shall be constructed in accordance with the regular code. Repairs or infills may be constructed in a similar manner to the original walls without conforming to the regular code.
SECTION 8-806 — ADOBE
8-806.1 General. Unburned clay masonry may be constructed, reconstructed, stabilized or rehabilitated subject to this chapter. Alternative approaches which provide an equivalent or greater level of safety may be used, subject to the concurrence of the enforcing agency.
8-806.2 Moisture protection. Provisions shall be in place to protect adobe structures from deterioration due to moisture penetration. Adobe shall be maintained in reasonably good condition. Particular attention shall be given to moisture content of adobe walls. Unmaintained walls or ruins shall be evaluated for safety based on their condition and stability. Additional protection measures may be appropriate subject to the concurrence of the enforcing agency.
8-806.3 Height to thickness ratio. Unreinforced new or existing adobe walls meeting these criteria need not be evaluated for out of plane failure. Where existing dimensions do not meet these conditions, additional strengthening measures, such as a bond beam, may be appropriate. Existing sod or rammed earth walls shall be considered similar to the extent these provisions apply.
- One-story adobe load-bearing walls shall not exceed a height-to-thickness ratio of 6.
- Two-story adobe buildings or structures’ height- to-thickness wall ratio shall not exceed 6 at the ground floor and 5 at the second floor, and shall be measured at floor-to-floor height when the second floor and attic ceiling/roof are connected to the wall as described below.
8-806.4 Nonload-bearing adobe. Nonload-bearing adobe partitions and gable end walls shall be evaluated for stability and anchored against out-of-plane failure if necessary.
8-806.5 Bond beam. Where provided, a bond beam or equivalent structural element shall be located at the top of all adobe walls, and at the second floor for two-story buildings or structures. The size and configuration of the structural element shall be sufficient to provide an effective brace for the wall, to tie the building together and to connect the wall to the floor or roof.
8-806.6 Repair or reconstruction. Repair or reconstruction of wall area may utilize unstabilized brick or adobe masonry designed to be compatible with the constituents of the existing adobe materials.
8-806.7 Shear values. Existing adobe may be allowed a maximum strength level of 12 pounds per square inch (82.7 kPa) for shear.
8-806.8 Mortar. Mortar may be of the same soil composition as that used in the existing wall, or in new walls as necessary to be compatible with the adobe brick.
SECTION 8-807 — WOOD
8-807.1 Existing wood diaphragms or walls. Existing wood diaphragms or walls of straight or diagonal sheathing shall be assigned shear resistance values appropriate with the fasteners and materials functioning in conjunction with the sheathing. The structural survey shall determine fastener details and spacings and verify a load path through floor construction. Shear values of Tables 8-8-A and 8-8-B.
8-807.2 Wood lath and plaster. Wood lath and plaster walls and ceilings may be utilized using the shear values referenced in Section 8-807.1.
CHBC § 8-805.2 High relevance — show source text
8-805.2 Stone masonry.
8-805.2.1 Solid-backed stone masonry. Stone masonry solidly backed with brick masonry shall be treated as solid brick masonry as described in Section 8-805.1 and in the 2009 International Existing Building Code [®] (IEBC [®] ), provided representative testing and inspection verifies solid collar joints between stone and brick and that a reasonable number of stones lap with the brick wythes as headers or that steel anchors are present. Solid stone masonry where the wythes of stone effectively overlap to provide the equivalent header courses may also be treated as solid brick masonry.
8-805.2.2 Independent wythe stone masonry. Stone masonry with independent face wythes may be treated as solid brick masonry as described in Section 8-805.1 and the CEBC, provided representative testing and inspection verify that the core is essentially solid in the masonry wall and that steel ties are epoxied in drilled holes between outer stone wythes at floors, roof and not to exceed 4 feet (1219 mm) on center in each direction, between floors and roof. A reinforcing element shall exist or be provided at or near the top of all stone masonry walls.
2025 CALIFORNIA HISTORICAL BUILDING CODE 15
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
ARCHAIC MATERIALS AND METHODS OF CONSTRUCTION
8-805.2.3 Testing of stone masonry. Testing of stone masonry shall be similar to the 2010 CEBC requirements for brick masonry, except that representative stones which are not interlocked shall be pulled outward from the wall and shear area appropriately calculated after the test.
8-805.3 Reconstructed walls. Totally reconstructed walls utilizing original brick or masonry, constructed similar to original, shall be constructed in accordance with the regular code. Repairs or infills may be constructed in a similar manner to the original walls without conforming to the regular code.
SECTION 8-806 — ADOBE
8-806.1 General. Unburned clay masonry may be constructed, reconstructed, stabilized or rehabilitated subject to this chapter. Alternative approaches which provide an equivalent or greater level of safety may be used, subject to the concurrence of the enforcing agency.
8-806.2 Moisture protection. Provisions shall be in place to protect adobe structures from deterioration due to moisture penetration. Adobe shall be maintained in reasonably good condition. Particular attention shall be given to moisture content of adobe walls. Unmaintained walls or ruins shall be evaluated for safety based on their condition and stability. Additional protection measures may be appropriate subject to the concurrence of the enforcing agency.
8-806.3 Height to thickness ratio. Unreinforced new or existing adobe walls meeting these criteria need not be evaluated for out of plane failure. Where existing dimensions do not meet these conditions, additional strengthening measures, such as a bond beam, may be appropriate. Existing sod or rammed earth walls shall be considered similar to the extent these provisions apply.
- One-story adobe load-bearing walls shall not exceed a height-to-thickness ratio of 6.
- Two-story adobe buildings or structures’ height- to-thickness wall ratio shall not exceed 6 at the ground floor and 5 at the second floor, and shall be measured at floor-to-floor height when the second floor and attic ceiling/roof are connected to the wall as described below.
CHBC § 2109.1.1 Medium relevance — show source text
2109.1.1 Limitations. The use of empirical design of adobe masonry shall be limited as noted in Section A.1.2 of TMS 402—16. In buildings that exceed one or more of the limitations of Section A.1.2 of TMS 402—16, masonry shall be designed in accordance with the engineered design provisions of Section 2101.2 or the foundation wall provisions of Section 1807.1.5.
Section A.1.2.3 of TMS 402—16 shall be modified as follows:
A.1.2.3 – Wind. Empirical requirements shall not apply to the design or construction of masonry for buildings, parts of buildings, or other structures to be located in areas where V asd as determined in accordance with Section 1609.3.1 of the California Building Code exceeds 110 mph.
2109.2 Adobe construction. Adobe construction shall comply with this section and shall be subject to the requirements of this code for Type V construction, Appendix A of TMS 402—16, and this section.
2109.2.1 Unstabilized adobe. Unstabilized adobe shall comply with Sections 2109.2.1.1 through 2109.2.1.4.
2109.2.1.1 Compressive strength. Adobe units shall have an average compressive strength of 300 psi (2068 kPa) when tested in accordance with ASTM C67. Five samples shall be tested and individual units are not permitted to have a compressive strength of less than 250 psi (1724 kPa).
2109.2.1.2 Modulus of rupture. Adobe units shall have an average modulus of rupture of 50 psi (345 kPa) when tested in accordance with the following procedure. Five samples shall be tested and individual units shall not have a modulus of rupture of less than 35 psi (241 kPa).
2109.2.1.2.1 Support conditions. A cured unit shall be simply supported by 2-inch-diameter (51 mm) cylindrical supports located 2 inches (51 mm) in from each end and extending the full width of the unit.
2109.2.1.2.2 Loading conditions. A 2-inch-diameter (51 mm) cylinder shall be placed at midspan parallel to the supports.
2109.2.1.2.3 Testing procedure. A vertical load shall be applied to the cylinder at the rate of 500 pounds per minute (37 N/s) until failure occurs.
2109.2.1.2.4 Modulus of rupture determination. The modulus of rupture shall be determined by the equation: Equation 21-2 f r = 3 PL s /[2 S w ( S t 2 )]
2109.2.1.3 Moisture content requirements. Adobe units shall have a moisture content not exceeding 4 percent by weight.
2109.2.1.4 Shrinkage cracks. Adobe units shall not contain more than three shrinkage cracks and any single shrinkage crack shall not exceed 3 inches (76 mm) in length or [1] / 8 inch (3.2 mm) in width.
CHBC § 0.35 Medium relevance — show source text
Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|For SI: 1 inch = 25.4 mm, 1 mile per hour = 0.447 m/s, 1 foot = 304.8 mm, 1 mil = 0.0254 mm.
a. Ceiling diaphragm is composed of1/2-inch gypsum board (min. thickness) secured with screws spaced at 6 inches o.c. at panel edges and 12 inches o.c. infield. Use No. 8
screws (min.) where framing members have a designation thickness of 54 mils or less and No. 10 screws (min.) where framing members have a designation thickness greater
than 54 mils.
b. Maximum aspect ratio (length/width) of diaphragms is 2:1.
c. Building width is in the direction of horizontal framing members supported by the wall studs.
d. Required diaphragm lengths are to be provided at each end of the structure.
e. Multiplying required diaphragm lengths by 0.35 is permitted if all panel edges are blocked.
f. Multiplying required diaphragm lengths by 0.9 is permitted if all panel edges are secured with screws spaced at 4 inches o.c.
g. To determine the minimum diaphragm length for buildings with ceiling heights of 9 feet or 10 feet values in this table shall be multiplied by 1.15.|FIGURE R804.3.7.1(1)—CEILING DIAPHRAGM TO GABLE ENDWALL DETAIL
CEILING JOISTS
FLAT STUD OR TRACK BLOCKING AT 48 IN. O.C. AT FIRST TWO JOIST SPACES
CHBC § 2108.2 Medium relevance — show source text
Exception: AAC masonry shall comply with the requirements of Chapters 1 through 7 and Chapter 11 of TMS 402.
2108.2 TMS 402, Section 6.1.6, development. Add a second paragraph to Section 6.1.6 as follows:
The required development length of reinforcement need not be greater than 72 d b .
2108.3 TMS 402, Section 6.1.6.1.1, splices. Add to Sections 6.1.7.2.1 and 6.1.7.3.1 as follows:
6.1.7.3.1 – Welded splices shall not be permitted in plastic hinge zones of intermediate or special reinforced walls.
6.1.7.2.1 – Mechanical splices shall be classified as Type 1 or 2 in accordance with Section 18.2.7.1 of ACI 318. Type 1 mechanical splices shall not be used within a plastic hinge zone or within a beam-column joint of intermediate or special reinforced masonry shear walls. Type 2 mechanical splices are permitted in any location within a member.
21-8 2025 CALIFORNIA BUILDING CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
SECTION 2109—EMPIRICAL DESIGN OF ADOBE MASONRY
[OSHPD 1R, 2 & 5] Not permitted by OSHPD .
2109.1 General. Empirically designed adobe masonry shall conform to the requirements of Appendix A of TMS 402—16, except where otherwise noted in this section.
2109.1.1 Limitations. The use of empirical design of adobe masonry shall be limited as noted in Section A.1.2 of TMS 402—16. In buildings that exceed one or more of the limitations of Section A.1.2 of TMS 402—16, masonry shall be designed in accordance with the engineered design provisions of Section 2101.2 or the foundation wall provisions of Section 1807.1.5.
Section A.1.2.3 of TMS 402—16 shall be modified as follows:
A.1.2.3 – Wind. Empirical requirements shall not apply to the design or construction of masonry for buildings, parts of buildings, or other structures to be located in areas where V asd as determined in accordance with Section 1609.3.1 of the California Building Code exceeds 110 mph.
2109.2 Adobe construction. Adobe construction shall comply with this section and shall be subject to the requirements of this code for Type V construction, Appendix A of TMS 402—16, and this section.
2109.2.1 Unstabilized adobe. Unstabilized adobe shall comply with Sections 2109.2.1.1 through 2109.2.1.4.
2109.2.1.1 Compressive strength. Adobe units shall have an average compressive strength of 300 psi (2068 kPa) when tested in accordance with ASTM C67. Five samples shall be tested and individual units are not permitted to have a compressive strength of less than 250 psi (1724 kPa).
California Historical Building Code Medium relevance — show source text
; 2′ C.R.S. with 1″ cover on
both top and bottom flanges; 13′1″ span
restrained.|60 psf|2 hrs|||7|1, 3|2| |F/C-6-RC-34|61/4″|61/4″ thick; 43/4″ (5120 psi) concrete core;
1″ T&G board flooring;1/2″ plaster under-
coat; 4″ × 3″ × 10 lbs R.S.J.; 3′ C.R.S. flush
with top surface concrete; 12′ span simply
supported; 2″ × 1′3″ clinker concrete
insert.|100 psf|4 hrs|||7|1, 7|4| |F/C-6-RC-35|61/4″|43/4″ (3600 psi) concrete core; 1″ T&G
board flooring;1/2″ plaster undercoat; 4″ ×
3″ × 10 lbs R.S.J.; 3′ C.R.S. flush with top
surface concrete; 12′ span simply
supported; 2″ × 1′3″ clinker concrete
insert.|100 psf|2 hrs
30 min|||7|1, 5|21/2| |F/C-6-RC-36|61/4″|43/4″ (2800 psi) concrete core; 1″ T&G
board flooring;1/2″ plaster undercoat; 4″ ×
3″ × 10 lbs R.S.J.; 3′ C.R.S. flush with top
surface concrete; 12″ span simply
supported; 2″ × 1′3″ clinker concrete
insert.|80 psf|4 hrs|||7|1, 7|4| |F/C-7-RC-37|7″|(3640 psi) concrete deck;1/4″ reinforce-
ment bars at 6″ pitch with 11/2″ cover;1/4″
reinforcement bars at 5″ pitch perpendic-
ular with 11/2″ cover; 13′1″ span
restrained.|169 psf|6 hrs|||7|1, 14|6| |F/C-7-RC-38|7″|(4060 psi) concrete deck; 4″ × 3″ × 10 lbs
R.S.J.; 2′6″ C.R.S. with 11/2″ cover on both
top and bottom flanges; 4″ × 6″ × 13 SWG
mesh reinforcement 11/2″ from bottom of
slab; 13′1″ span restrained.|175 psf|6 hrs|||7|1, 14|6| |F/C-7-RC-39|71/4″|53/4″ (4010 psi) concrete core; 1″ T&G
board flooring;1/2″ plaster undercoat;
4″ × 3″ × 10 lbs R.S.J.; 2′6″ C.R.S.CHBC § 8-8 Medium relevance — show source text
CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15
Section
8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15
8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-809 Steel and Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-810 Hollow Clay Tile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-811 Veneers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8-812 Glass and Glazing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
CHAPTER 8-9 MECHANICAL, PLUMBING AND ELECTRICAL REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . 19
Section
8-901 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 19 8-902 Mechanical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8-903 Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 8-904 Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
CHAPTER 8-10 QUALIFIED HISTORICAL DISTRICTS,
SITES AND OPEN SPACES . . . . . . . . . . . . . . . 23
Section
CHBC § 2109.2.3.1 Medium relevance — show source text
TABLE 2109.2.3.1—ALLOWABLE SHEAR ON BOLTS IN ADOBE MASONRY Col2 Col3 DIAMETER OF BOLTS (inches) MINIMUM EMBEDMENT (inches) SHEAR (pounds) 1/2 — — 5/8 12 200 3/4 15 300 7/8 18 400 1 21 500 11/8 24 600 For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. For SI: 1 inch = 25.4 mm, 1 pound = 4.448 N. 2109.2.4 Detailed requirements. Adobe construction shall comply with Sections 2109.2.4.1 through 2109.2.4.9.
2109.2.4.1 Number of stories. Adobe construction shall be limited to buildings not exceeding one story, except that two-story construction is allowed where designed by a registered design professional.
2025 CALIFORNIA BUILDING CODE 21-9
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
MASONRY
2109.2.4.2 Mortar. Mortar for adobe construction shall comply with Sections 2109.2.4.2.1 and 2109.2.4.2.2.
2109.2.4.2.1 General. Mortar for adobe units shall be in accordance with Section 2103.2.1, or be composed of adobe soil of the same composition and stabilization as the adobe brick units. Unstabilized adobe soil mortar is permitted in conjunction with unstabilized adobe brick units.
2109.2.4.2.2 Mortar joints. Adobe units shall be laid with full head and bed joints and in full running bond.
2109.2.4.3 Parapet walls. Parapet walls constructed of adobe units shall be waterproofed.
2109.2.4.4 Wall thickness. The minimum thickness of exterior walls in one-story buildings shall be 10 inches (254 mm). The walls shall be laterally supported at intervals not exceeding 24 feet (7315 mm). The minimum thickness of interior load-bearing walls shall be 8 inches (203 mm). The unsupported height of any wall constructed of adobe units shall not exceed 10 times the thickness of such wall.
2109.2.4.5 Foundations. Foundations for adobe construction shall be in accordance with Sections 2109.2.4.5.1 and
2109.2.4.5.2.
2109.2.4.5.1 Foundation support. Walls and partitions constructed of adobe units shall be supported by foundations or footings that extend not less than 6 inches (152 mm) above adjacent ground surfaces and are constructed of solid masonry (excluding adobe) or concrete. Footings and foundations shall comply with Chapter 18.
2109.2.4.5.2 Lower course requirements. Stabilized adobe units shall be used in adobe walls for the first 4 inches (102 mm) above the finished first-floor elevation.
California Historical Building Code Medium relevance — show source text
; 2′6″ C.R.S. with 1″ cover on
both top and bottom flanges; 12′ span
simply supported.|115 psf|29 min|||7|1, 5,
13|1/4| |F/C-6-RC-31|6″|6″ deep (3450 psi) concrete deck; 4″ ×
13/4″ × 5 lbs R.S.J.; 2′6″ C.R.S. with 1″ cover
on both top and bottom flanges; 12′ span
simply supported.|25 psf|3 hrs
35 min|||7|1, 2|31/2| |F/C-6-RC-32|6″|6″ deep (4460 psi) concrete deck; 4″ ×
13/4″ × 5 lbs R.S.J.; 2′ C.R.S. with 1″ cover
on both top and bottom flanges; 12′ span
simply supported.|60 psf|4 hrs
30 min|||7|1, 10|41/2| |F/C-6-RC-33|6″|6″ deep (4360 psi) concrete deck; 4″ × 13/4″
× 5 lbs R.S.J.; 2′ C.R.S. with 1″ cover on
both top and bottom flanges; 13′1″ span
restrained.|60 psf|2 hrs|||7|1, 3|2| |F/C-6-RC-34|61/4″|61/4″ thick; 43/4″ (5120 psi) concrete core;
1″ T&G board flooring;1/2″ plaster under-
coat; 4″ × 3″ × 10 lbs R.S.J.; 3′ C.R.S. flush
with top surface concrete; 12′ span simply
supported; 2″ × 1′3″ clinker concrete
insert.|100 psf|4 hrs|||7|1, 7|4| |F/C-6-RC-35|61/4″|43/4″ (3600 psi) concrete core; 1″ T&G
board flooring;1/2″ plaster undercoat; 4″ ×
3″ × 10 lbs R.S.J.; 3′ C.R.S. flush with top
surface concrete; 12′ span simply
supported; 2″ × 1′3″ clinker concrete
insert.|100 psf|2 hrs
30 min|||7|1, 5|21/2| |F/C-6-RC-36|61/4″|43/4″ (2800 psi) concrete core; 1″ T&G
board flooring;1/2″ plaster undercoat; 4″ ×
3″ × 10 lbs R.S.J.; 3′ C.R.S.CHBC § 8-6 Medium relevance — show source text
CHAPTER 8-6 ACCESSIBILITY . . . . . . . . . . . . . . . . . . . . . . . . 11
Section
8-601 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 11
8-602 Basic Provisions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8-603 Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8-604 Equivalent Facilitation. . . . . . . . . . . . . . . . . . . . . . . . . . 12
CHAPTER 8-7 STRUCTURAL REGULATIONS. . . . . . . . . . . . . 13
Section
8-701 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 13 8-702 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8-703 Structural Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-704 Nonhistorical Additions and
Nonhistorical Alterations . . . . . . . . . . . . . . . . . . . . . . . 13
8-705 Structural Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . 13 8-706 Lateral Load Regulations. . . . . . . . . . . . . . . . . . . . . . . . 14
CHAPTER 8-8 ARCHAIC MATERIALS AND METHODS OF
CONSTRUCTION . . . . . . . . . . . . . . . . . . . . . . . 15
Section
8-801 Purpose, Intent and Scope . . . . . . . . . . . . . . . . . . . . . . 15 8-802 General Engineering Approaches. . . . . . . . . . . . . . . . . 15 8-803 Nonstructural Archaic Materials. . . . . . . . . . . . . . . . . . 15
8-804 Allowable Conditions for Specific Materials . . . . . . . 15 8-805 Masonry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8-806 Adobe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-807 Wood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8-808 Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Frequently asked questions
Does the CHBC state a maximum allowable moisture percentage for adobe?
No. § 8-806.2 requires attention to moisture and protective measures but does not specify a numeric moisture percentage. For laboratory/test numeric limits commonly used in engineering evaluations, see the California Building Code (for example CBC § 2109.2.1.3 which references 4% moisture by weight for adobe units).
What if the historic repair method uses unstabilized soil mortar inconsistent with modern materials?
The CHBC permits mortar compatible with existing adobe materials and allows repair methods that match historic practice where appropriate; alternative approaches that provide equivalent or greater safety may be used with enforcing agency concurrence. § 8-806.6 and § 8-806.1 apply.
Who decides what “additional protection measures” are required?
The enforcing agency (building official) must concur on alternative approaches and may require additional protection measures when CHBC § 8-806.2 identifies unmaintained or deteriorated walls needing evaluation and action. Documented inspection and a proposed plan are typically reviewed by that agency.
If I find a ruined adobe wall on my property, can I rebuild it exactly as it was?
Totally reconstructed walls using original materials constructed similar to original may need to comply with the regular code; repairs or infills may be allowed in a similar manner to the original without full compliance. Confirm with the enforcing agency and reference CHBC reconstruction guidance.
Should moisture-control details (e.g., capillary breaks, drainage) be included on permit drawings for CHBC projects?
Yes — because § 8-806.2 requires provisions to protect adobe from moisture, include proposed moisture-control measures in plans and get enforcing-agency concurrence for alternatives. Specific prescriptive details may reference other codes or accepted conservation practice.
More in California Historical Building Code
Ask about the CHBC
Get cited, plain-English answers on the California Historical Building Code for your project — any code section, any scenario.
Start Free Trial