CRC · California Residential Code
Concrete slabs on grade: design and construction requirements
For homeowners: California's Residential Code (CRC § R506) requires most residential concrete slabs on grade to be at least 3 1/2 inches thick, built on a properly prepared subgrade with limits on fill, have a 4‑inch base when below grade, and use a 6‑mil vapor retarder where required. Post‑tensioned slabs and detailed reinforcement or strength requirements must follow the referenced standards (PTI DC10.5 or ACI 332 and § R402.2 for concrete strength) — check the specific CRC sections cited for exceptions and site‑specific rules.
Last reviewed: July 6, 2026
What the code requires — 2-4 sentences
Concrete slab‑on‑ground floors must be designed and built to the requirements of § R506 of the California Residential Code (CRC). The slab thickness shall be not less than 3 1/2 inches (89 mm) and the specified concrete compressive strength is set by § R402.2; post‑tensioned slabs must be designed per PTI DC10.5 as required by § R506.2. Site preparation (removal of vegetation/topsoil), limits on fill depth, a 4‑inch base where the slab is below grade, and a 6‑mil vapor retarder where required are all spelled out in § R506.3 and its subsections .
The single most important rule: a slab on grade for a residence must meet the minimum thickness (3 1/2 in) and the site, base, vapor‑retarder and reinforcement support requirements in § R506, unless the slab is designed under the referenced standards (ACI 332/PTI DC10.5) .
Requirements in detail
Governing language and referenced standards
- Design and construction must follow § R506 or ACI 332 (plain‑concrete slab guidance) — see § R506.1 .
- Post‑tensioned slab‑on‑ground floors require design to PTI DC10.5 per § R506.2 .
- Specified concrete compressive strength is governed by § R402.2 (refer to the CRC tables for minimum f'c values) .
Site preparation (what to do before placing slab)
- Remove all vegetation, topsoil and foreign material from the area inside foundation walls — § R506.3 .
- Fill must be free of vegetation/foreign material and compacted to provide uniform support. Fill depth limits (unless approved otherwise) are: 24 inches (610 mm) for clean sand or gravel, and 8 inches (203 mm) for earth — § R506.3.1 .
- Where the slab is below grade, a 4‑inch (102 mm) base course of clean graded sand, gravel, crushed stone, crushed concrete or crushed blast‑furnace slag (passing a 2‑inch sieve) is required — § R506.3.2 .
Vapor retarder and capillary break
- Where a base course does not exist, install a minimum 6‑mil (0.006 in; 152 μm) polyethylene or approved vapor retarder, with joints lapped not less than 6 inches (152 mm), between the slab and the base/subgrade — § R506.3.3 .
- The code lists exceptions where the vapor retarder is not required (garages, small unheated storage < 70 sq ft, carports, exterior flatwork not likely to be enclosed, or where the building official approves based on local conditions) — § R506.3.3 .
- When a vapor retarder is required, a capillary break must be installed in accordance with the California Green Building Standards Code (referenced from § R506.3.3.1) .
Reinforcement support and placement
- If reinforcement is used in a slab‑on‑ground, it must be supported so it remains from the center to the upper one‑third of the slab thickness for the duration of concrete placement — § R506.3.4 .
- The CRC allows use of ACI 332 for design details (reinforcing sizes/spacing, joints, etc.) — see § R506.1 .
Compressive strength and other concrete properties
- The required concrete compressive strength for slabs is set by § R402.2 (refer to the CRC tables for location‑specific minimums; e.g., many interior slabs have a minimum of 2,500 psi at 28 days) — see § R402.2 for values and notes on air‑entrainment and special finishes .
Quick decision table (code reference)
| Item | Required value / action | Code Reference |
|---|---|---|
| Minimum slab thickness (typical) | 3 1/2 in (89 mm) | § R506.1 |
| Post‑tensioned slabs design standard | PTI DC10.5 | § R506.2 |
| Remove vegetation/topsoil | Required in area within foundation walls | § R506.3 |
| Fill depth limits (unless approved) | 24 in (clean sand/gravel); 8 in (earth) | § R506.3.1 |
| Base course where slab below grade | 4 in (102 mm) of clean graded material | § R506.3.2 |
| Vapor retarder (where base absent) | 6‑mil polyethylene; 6 in lap | § R506.3.3 |
| Vapor retarder exceptions | Garages, small unheated storage < 70 ft², carports, exterior flatwork, or BO approval | § R506.3.3 |
| Reinforcement support location | From center to upper 1/3 of slab | § R506.3.4 |
| Specified compressive strength (typ.) | See § R402.2 (e.g., 2,500 psi for many interior slabs) | § R402.2 |
Exceptions & special cases
- Base course not required where slab is installed on well‑drained or sand‑gravel mixture soils classified as Group I (USCS) — exception to § R506.3.2 .
- Vapor retarder not required for garages, unheated accessory structures, unheated storage < 70 ft², carports, exterior flatwork not likely to be enclosed, or where the building official approves based on local site conditions — exception to § R506.3.3 .
- For expansive soils, other provisions may control (see § R403.1.8 referenced from § R506.1) — R506 notes the connection to the foundation/soil provisions for such conditions .
- Post‑tensioned slabs are a separate category and must follow PTI guidance per § R506.2 .
Common mistakes
- Skipping a vapor retarder when the slab is over subgrade and a base course is absent — CRC requires a 6‑mil retarder unless an exception applies (§ R506.3.3) .
- Using loose or organic fill without removing vegetation/topsoil or without compaction; failing to respect the 24 in / 8 in fill depth limits in § R506.3.1 .
- Assuming the 4‑inch base is optional for below‑grade slabs — it is required unless the Group I soil exception applies (§ R506.3.2) .
- Not supporting reinforcement to the specified elevation (center to upper one‑third) so the steel ends up at the bottom of the slab — see § R506.3.4 .
- Confusing a vapor retarder with a structural capillary break: both are addressed but the capillary break requirement (when vapor retarder is required) refers to the California Green Building Standards Code (§ R506.3.3.1) .
- Overlooking that post‑tensioned slabs require a separate design standard (PTI DC10.5) under § R506.2 — do not attempt to treat a PT slab as plain slab without PTI design documentation .
Worked example — typical residential interior slab (numbers)
Scenario: New single‑story residence with a 20 ft × 30 ft (600 ft²) interior slab‑on‑grade living area, slab below grade on non‑Group‑I soils.
Apply CRC minimums from § R506:
- Slab thickness: use CRC minimum 3 1/2 in (0.2917 ft) (per § R506.1) .
- Base: install 4 in (0.3333 ft) aggregate base under the entire slab (per § R506.3.2) .
- Vapor retarder: place 6‑mil poly with 6 in lap between slab and base/subgrade (per § R506.3.3) .
- Reinforcement: if using wire mesh/rebar, support to remain between center and upper 1/3 of slab during placement (per § R506.3.4) .
- Concrete strength: specify concrete per § R402.2 (commonly 2,500 psi for interior slabs unless other conditions dictate) .
Estimated materials (approx.):
- Concrete volume = area × thickness = 600 ft² × 0.2917 ft = 175 ft³ = ≈ 6.48 yd³ of concrete.
- Base aggregate volume = 600 ft² × 0.3333 ft = 200 ft³ = ≈ 7.41 yd³ of base material.
- Vapor retarder: one 10 ft × 100 ft roll covers 1,000 ft² — you need one roll for 600 ft² plus overlap; ensure 6 in lap at seams and extra to extend to edges for proper placement.
Notes: if the soils report indicates expansive soil or other adverse conditions, comply with foundation/soil provisions (e.g., § R403.1.8) or provide engineered design; if post‑tensioned slab is selected, provide PTI DC10.5 design documentation per § R506.2 .
Related provisions (CRC / referenced)
- § R506.1 — General slab‑on‑ground requirements and reference to ACI 332
- § R506.2 — Post‑tensioned slab‑on‑ground design required to PTI DC10.5
- § R506.3 & subsections — Site preparation, fill, base, vapor retarder, reinforcement support
- § R402.2 — Specified compressive strengths (minimum f'c values) for concrete locations (interior slabs, garage slabs, etc.)
- § R403.1.8 — Expansive soil provisions referenced from § R506.1 (see foundation/soil sections)
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 3.8 High relevance — show source text
Each header joist shall be connected to trimmer joists with four 2-inch by 2-inch (51-mm by 51-mm) clip angles. Each clip angle shall be fastened to both the header and trimmer joists with four No. 8 screws, evenly spaced, through each leg of the clip angle. The clip angles shall have a thickness not less than that of the floor joist. Each track section for a built-up header or trimmer joist shall extend the full length of the joist (continuous).
FIGURE R505.3.8(1)—COLD-FORMED STEEL FLOOR CONSTRUCTION—6-FOOT FLOOR OPENING
JOIST
CLIP ANGLE
For SI: 1 foot = 304.8 mm.
For SI: 1 foot = 304.8 mm.
JOIST
FIGURE R505.3.8(2)—COLD-FORMED STEEL FLOOR CONSTRUCTION—8-FOOT FLOOR OPENING
JOIST
CLIP ANGLE
JOIST
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FLOORS
WITH 4 NO. 8 SCREWS THROUGH EACH LEG, BOTH SIDES OF CONNECTION
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
MINIMUM 2 IN. × 2 IN. CLIP ANGLE
WITH 4 NO. 8 SCREWS THROUGH EACH LEG, BOTH SIDES OF CONNECTION
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
(TYP.)
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FLOORS
SECTION R506—CONCRETE FLOORS (ON GROUND)
R506.1 General. Concrete slab-on-ground floors shall be designed and constructed in accordance with the provisions of this section or ACI 332. Such floors shall be not less than 3 [1] / 2 inches (89 mm) thick (for expansive soils, see Section R403.1.8). The specified compressive strength of concrete shall be as set forth in Section R402.2.
R506.2 Post-tensioned slab-on-ground floors. Post-tensioned concrete slabs-on-ground floors placed on expansive or stable soils shall be designed in accordance with PTI DC10.5.
R506.3 Site preparation. The area within the foundation walls shall have all vegetation, topsoil and foreign material removed.
R506.3.1 Fill. Fill material shall be free of vegetation and foreign material. The fill shall be compacted to ensure uniform support of the slab, and except where approved, the fill depths shall not exceed 24 inches (610 mm) for clean sand or gravel and 8 inches (203 mm) for earth.
R506.3.2 Base. A 4-inch-thick (102 mm) base course consisting of clean graded sand, gravel, crushed stone, crushed concrete or crushed blast-furnace slag passing a 2-inch (51 mm) sieve shall be placed on the prepared subgrade where the slab is below grade.
CRC § 25.4 High relevance — show source text
For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
(TYP.)
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FLOORS
SECTION R506—CONCRETE FLOORS (ON GROUND)
R506.1 General. Concrete slab-on-ground floors shall be designed and constructed in accordance with the provisions of this section or ACI 332. Such floors shall be not less than 3 [1] / 2 inches (89 mm) thick (for expansive soils, see Section R403.1.8). The specified compressive strength of concrete shall be as set forth in Section R402.2.
R506.2 Post-tensioned slab-on-ground floors. Post-tensioned concrete slabs-on-ground floors placed on expansive or stable soils shall be designed in accordance with PTI DC10.5.
R506.3 Site preparation. The area within the foundation walls shall have all vegetation, topsoil and foreign material removed.
R506.3.1 Fill. Fill material shall be free of vegetation and foreign material. The fill shall be compacted to ensure uniform support of the slab, and except where approved, the fill depths shall not exceed 24 inches (610 mm) for clean sand or gravel and 8 inches (203 mm) for earth.
R506.3.2 Base. A 4-inch-thick (102 mm) base course consisting of clean graded sand, gravel, crushed stone, crushed concrete or crushed blast-furnace slag passing a 2-inch (51 mm) sieve shall be placed on the prepared subgrade where the slab is below grade.
Exception: A base course is not required where the concrete slab is installed on well-drained or sand-gravel mixture soils classified as Group I according to the United Soil Classification System in accordance with Table R401.4.1(2).
R506.3.3 Vapor retarder. A minimum 6 mil (0.006 inch; 152 μ m) polyethylene or approved vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the concrete floor slab and the base course or the prepared subgrade where a base course does not exist.
Exception: The vapor retarder is not required for the following:
- Garages, utility buildings and other unheated accessory structures.
- For unheated storage rooms having an area of less than 70 square feet (6.5 m [2] ) and carports.
- Driveways, walks, patios and other flatwork not likely to be enclosed and heated at a later date.
- Where approved by the building official, based on local site conditions.
R506.3.3.1 Capillary break. When a vapor retarder is required, a capillary break shall be installed in accordance with the Califor- nia Green Building Standards Code, Chapter 4, Division 4.5.
R506.3.4 Reinforcement support. Where provided in slabs-on-ground, reinforcement shall be supported to remain in place from the center to upper one-third of the slab for the duration of the concrete placement.
SECTION R507—EXTERIOR DECKS
CRC § 25.4 Medium relevance — show source text
The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
o. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm, 1 pound per square foot per foot = 0.1571 kPa2/m, 1 pound per square inch = 6.895 kPa.
NR = Not Required.
DR = Design Required.
a. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
b. Table values are based on reinforcing bars with a minimum yield strength of 60,000 psi.
c. Vertical reinforcement with a yield strength of less than 60,000 psi and bars of a different size than specified in the table are permitted in accordance with Section
R404.1.3.3.7.6 and Table R404.1.3.2(9).
d. NR indicates vertical wall reinforcement is not required, except for 6-inch nominal walls formed with stay-in-place forming systems in which case vertical reinforcement shall
be No. 4@48 inches on center.
e. Allowable deflection criterion is_L_/240, where_L_ is the unsupported height of the basement wall in inches.
f. Interpolation is not permitted.
g. Where walls will retain 4 feet or more of unbalanced backfill, they shall be laterally supported at the top and bottom before backfilling.
h. Vertical reinforcement shall be located to provide a cover of 11/4 inches measured from the inside face of the wall. The center of the steel shall not vary from the specified loca-
tion by more than the greater of 10 percent of the wall thickness or3/8 inch.
i. Concrete cover for reinforcement measured from the inside face of the wall shall be not less than3/4 inch. Concrete cover for reinforcement measured from the outside face of
the wall shall be not less than 11/2 inches for No. 5 bars and smaller, and not less than 2 inches for larger bars.
j. DR means design is required in accordance with the applicable building code, or in the absence of a code, in accordance with ACI 318.
k. Concrete shall have a specified compressive strength,f′c, of not less than 2,500 psi at 28 days, unless a higher strength is required by Note l or m.
l. The minimum thickness is permitted to be reduced 2 inches, provided that the minimum specified compressive strength of concrete,f′c, is 4,000 psi.
m.A plain concrete wall with a minimum nominal thickness of 12 inches is permitted, provided that the minimum specified compressive strength of concrete,f′c, is 3,500 psi.
n. See Table R608.3 for tolerance from nominal thickness permitted for flat walls.
o.CRC § 8.8 Medium relevance — show source text
**
HOURS| |ITEM CODE|DEPTH|CONSTRUCTION DETAILS|LOAD|TIME|PRE-BMS-92|BMS-92|POST-BMS-92|POST-BMS-92|POST-BMS-92| |B-11-RC-1|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (3290 psi); details: see Note 5 figure.|8.8 tons|4 hrs
2 min|||7|1, 2, 14|4| |B-10-RC-2|10″|24″ wide × 10″ deep reinforced concrete “T”
beam (4370 psi); details: see Note 6 figure.|8.8 tons|1 hr
53
min|||7|1, 3|13/4| |B-10-RC-3|101/2″|24″ wide × 101/2″ deep reinforced concrete
“T” beam (4450 psi); details: see Note 7
figure.|8.8 tons|2 hrs
40
min|||7|1, 3|22/3| |B-11-RC-4|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (2400 psi); details: see Note 8 figure.|8.8 tons|3 hrs
32
min|||7|1, 3, 14|31/2| |B-11-RC-5|11″|24″ wide × 11″ deep reinforced concrete “T”
beam (4250 psi); details: see Note 9 figure.|8.8 tons|3 hrs
3 min|||7|1, 3, 14|3| |B-11-RC-6|11″|Concrete flange: 4″ deep × 2' wide (4895 psi)
concrete; concrete beam: 7″ deep × 61/2″
wide; “I” beam reinforcement; 10″ × 41/2″ ×
25 lbs R.S.J.; 1″ cover on flanges; flange rein-
forcement:3/8″ diameter bars at 6″ pitch
parallel to “T”; 1/4″ diameter bars perpendic-
ular to “T”; beam reinforcement: 4″ × 6″ No.
13 SWG wire mesh; span: 11' restrained;
details: see Note 10 figure.|10 tons|6 hrs|||7|1, 4|6| |B-11-RC-7|11″|Concrete flange: 6″ deep × 1' 61/2″ wide (3525
psi) concrete; concrete beam: 5″ deep × 8″
wide precast concrete blocks 83/4″ long; “I”
beam reinforcement; 7″ × 4″ × 16 lbs R.S.J.CRC § 3.1 Medium relevance — show source text
10|23/4| |F/C-6-RC-25|6″|6″ deep (4800 psi) concrete deck;1/4″ rein-
forcement bars at 71/2″ pitch with7/8″
cover;3/8″ main reinforcement bars at
31/2″ pitch perpendicular with7/8″ cover;
13′1″ span restrained.|195
psf|4 hrs|||7|1, 7|4| |F/C-6-RC-26|6″|6″ (4650 psi) concrete deck;1/4″ reinforce-
ment bars at 71/2″ pitch with7/8″ cover;3/8″
main reinforcement bars at 31/2″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|195
psf|2 hrs
23 min|||7|1, 2|21/4| |F/C-6-RC-27|6″|6″ deep (6050 psi) concrete deck;1/4″ rein-
forcement bars at 71/2″ pitch with7/8″
cover;3/8″ reinforcement bars at 31/2″
pitch perpendicular with1/2″ cover; 13′1″
span restrained.|195
psf|3 hrs
30 min|||7|1, 10|31/2| |F/C-6-RC-28|6″|6″ deep (5180 psi) concrete deck;1/4″ rein-
forcement bars at 8″ pitch with3/4″ cover;
1/4″ reinforcement bars at 51/2″ pitch
perpendicular with1/2″ cover; 13′1″ span
restrained.|150
psf|4 hrs|||7|1, 7|4|2025 CALIFORNIA EXISTING BUILDING CODE RESOURCE A-93
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RESOURCE A—GUIDELINES ON FIRE RATINGS OF ARCHAIC MATERIALS AND ASSEMBLIES
TABLE 3.1—continued
FLOOR/CEILING ASSEMBLIES—REINFORCED CONCRETECol2 Col3 Col4 Col5 Col6 Col7 Col8 Col9 Col10 ITEM
CODEASSEMBLY
THICKNESSCONSTRUCTION DETAILS PERFORMANCE PERFORMANCE REFERENCE NUMBER REFERENCE NUMBER REFERENCE NUMBER NOTES REC.
HOURSITEM
CODEASSEMBLY
THICKNESSCONSTRUCTION DETAILS LOAD TIME PRE-BMS-92 BMS-92 POST-BMS-92 POST-BMS-92 POST-BMS-92 F/C-6-RC-29 6″ 6″ thick (4180 psi) concrete deck; 4″ × 3″ ×
10 lbs R.S.J.; 2′6″ C.R.S.CRC § 3.5 Medium relevance — show source text
BF105.2 Footings. In areas with a frostline depth of zero as specified in Table R301.2, for patio covers supported on a slab-on-grade without footings, the slab shall conform to the provisions of Section R506, shall be not less than 3.5 inches (89 mm) thick and the columns shall not support live and dead loads in excess of 750 pounds (3.34 kN) per column.
SECTION BF106—SPECIAL PROVISIONS FOR ALUMINUM SCREEN ENCLOSURES IN HURRICANE-PRONE REGIONS
BF106.1 General. Screen enclosures in hurricane-prone regions shall be in accordance with the provisions of this section.
BF106.1.1 Habitable spaces. Screen enclosures shall not be considered habitable spaces.
BF106.1.2 Minimum ceiling height. Screen enclosures shall have a ceiling height of not less than 7 feet (2134 mm).
BF106.2 Definition. The following word and term shall, for the purposes of this appendix, have the meaning shown herein.
SCREEN ENCLOSURE. A building or part thereof, in whole or in part self-supporting, and having walls of insect screening, and a roof of insect screening, plastic, aluminum or similar lightweight material.
BF106.3 Screen enclosures. Screen enclosures shall comply with Sections BF106.3.1 and BF106.3.2.
BF106.3.1 Thickness. Actual wall thickness of extruded aluminum members shall be not less than 0.040 inch (1.02 mm).
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APPENDIX BF — PATIO COVERS
BF106.3.2 Density. Screen density shall be not more than 20 threads per inch by 20 threads per inch mesh.
BF106.4 Design. The structural design of screen enclosures shall comply with Sections BF106.4.1 through BF106.4.3.
BF106.4.1 Wind load. Structural members supporting screen enclosures shall be designed to support the minimum wind loads given in Tables BF106.4.1(1) and BF106.4.1(2) for the ultimate design wind speed, V ult, determined from Figure BF106.4.1. Where any value is less than 10 pounds per square foot (psf) (0.479 kN/m [2] ) use 10 pounds per square foot (0.479 kN/m [2] ).
FIGURE BF106.4.1—ULTIMATE DESIGN WIND SPEEDS FOR PATIO COVERS AND SCREEN ENCLOSURES
For SI: 1 foot = 304.8 mm, 1 mph = 0.447 m/s. Notes:
- Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 feet above ground for Exposure C category.
- Linear interpolation between contours is permitted.
- Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area.
- Mountainous terrain, gorges, ocean promontories and special wind regions shall be examined for unusual wind conditions.
- Wind speeds correspond to approximately a 7-percent probability of exceedance in 50 years (Annual Exceedance Probability = 0.00143, MRI = 700 years).
|TABLE BF106.4.
CRC § 4.2 Medium relevance — show source text
BF106.4.2 Deflection limit. For members supporting screen surfaces only, the total load deflection shall not exceed l /60. Screen surfaces shall be permitted to include not more than 25-percent solid flexible finishes. BF106.4.3 Roof live load. The roof live load shall be not less than 10 psf (0.479 kN/m [2] ).
BF106.5 Footings. In areas with a frost line depth of zero, screen enclosures supported on a concrete slab-on-grade without footings shall conform to the provisions of Section R506, be not less than 3 [1] / 2 inches (89 mm) thick and the columns shall not support loads in excess of 750 pounds (3.36 kN) per column.
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APPENDIX BF-6 2025 CALIFORNIA RESIDENTIAL CODE
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CALIFORNIA RESIDENTIAL CODE – MATRIX ADOPTION TABLE
APPENDIX BG – SOUND TRANSMISSION
(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.
Adopting agency BSC BSC-
CGSFM HCD Col6 Col7 DSA Col9 Col10 OSHPD Col12 Col13 Col14 Col15 Col16 BSCC DPH AGR DWR CEC CA SL SLC Adopting agency BSC BSC-
CGSFM 1 2 1/AC AC SS SS/CC 1 1R 2 3 4 5 5 5 5 5 5 5 5 5 Adopt entire chapter Adopt entire chapter as
amended (amended
sections listed below)Adopt only those sections
that are listed belowChapter / Section 2025 CALIFORNIA RESIDENTIAL CODE APPENDIX BG-1
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APPENDIX BG-2 2025 CALIFORNIA RESIDENTIAL CODE
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BG SOUND TRANSMISSION
The provisions contained in this appendix are not mandatory unless specifically a dopted by a state agency or referenced in the adopting ordinance.
See Section 1206 “Sound Transmission” of the California Building Code, Title 24, Part 2, for requirements applicable to structures in this code.
CRC § 1.3.2.2 Medium relevance — show source text
Where unbalanced backfill retained by the stem wall is less than or equal to 18 inches (457 mm), the stem wall and above-grade wall it supports shall be provided with vertical reinforcement in accordance with Section R608.6 and Table R608.6(1), R608.6(2) or R608.6(3) for above-grade walls. Where unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the stem wall and above-grade wall it supports shall be provided with vertical reinforcement in accordance with Section R608.6 and Table R608.6(1).
- Stem walls laterally supported at top. Concrete stem walls that are monolithic with slabs-on-ground or are otherwise laterally supported by slabs-on-ground shall be vertically reinforced in accordance with Section R608.6 and Table R608.6(1), R608.6(2) or R608.6(3) for above-grade walls. Where the unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the connection between the stem wall and the slab-on-ground, and the portion of the slab-on-ground providing lateral support for the wall shall be designed in accordance with PCA 100 or with accepted engineering practice. Where the unbalanced backfill retained by the stem wall is greater than 18 inches (457 mm), the minimum nominal thickness of the wall shall be 6 inches (152 mm).
R404.1.3.2.2 Concrete foundation stem walls supporting light-frame above-grade walls. Concrete foundation stem walls that support light-frame above-grade walls shall be designed and constructed in accordance with this section.
- Stem walls not laterally supported at top. Concrete stem walls that are not monolithic with slabs-on-ground or are not otherwise laterally supported by slabs-on-ground and retain 48 inches (1219 mm) or less of unbalanced fill, measured from the top of the wall, shall be constructed in accordance with Section R404.1.3. Foundation stem walls that retain more than 48 inches (1219 mm) of unbalanced fill, measured from the top of the wall, shall be designed in accordance with Sections R404.1.1 and R404.4.
- Stem walls laterally supported at top. Concrete stem walls that are monolithic with slabs-on-ground or are otherwise laterally supported by slabs-on-ground shall be constructed in accordance with Section R404.1.3. Where the unbalanced backfill retained by the stem wall is greater than 48 inches (1219 mm), the connection between the stem wall and the slab-on-ground, and the portion of the slab-on-ground providing lateral support for the wall, shall be designed in accordance with PCA 100 or in accordance with accepted engineering practice.
R404.1.3.3 Concrete, materials for concrete, and forms. Materials used in concrete, the concrete itself and forms shall conform to requirements of this section or ACI 318.
R404.1.3.3.1 Compressive strength. The minimum specified compressive strength of concrete, f ′ c, shall comply with Section R402.2 and shall be not less than 2,500 psi (17.2 MPa) at 28 days in buildings assigned to Seismic Design Category A, B or C and 3,000 psi (20.5 MPa) in buildings assigned to Seismic Design Category D 0, D 1 or D 2 .
R404.1.3.3.2 Concrete mixing and delivery. Mixing and delivery of concrete shall comply with ASTM C94 or ASTM C685.
CRC § 2.4. Medium relevance — show source text
2.4. Anchors are located a minimum of 15 anchor diameters from the edge of the concrete perpendicular to the length of the track. 2.5. The track is 33 to 68 mil (0.84 mm to 1.73 mm) designation thickness. 3. In light-frame construction bearing or nonbearing walls, shear strength of concrete anchors less than or equal to 1 inch (25 mm) in diameter attaching sill plate or track to foundation or foundation stemwalls need not satisfy Sections 17.10.6.3(a) through (c) when the design strength of the anchors is determined in accordance with Section 17.7.2.1(c) of ACI 318.
SECTION 1906—FOOTINGS FOR LIGHT-FRAME CONSTRUCTION
[OSHPD 1R, 2 & 5] Plain concrete footings not permitted by OSHPD.
1906.1 Plain concrete footings. For Group R-3 occupancies and buildings of other occupancies less than two stories above grade plane of light-frame construction, the required thickness of plain concrete footings is permitted to be 6 inches (152 mm), provided that the footing does not extend more than 4 inches (102 mm) on either side of the supported wall.
SECTION 1907—SLABS-ON-GROUND
1907.1 Structural slabs-on-ground. Structural concrete slabs-on-ground shall comply with all applicable provisions of this chapter. Slabs-on-ground shall be considered structural concrete where required by ACI 318 or where designed to transmit either of the following:
- Vertical loads or lateral forces from other parts of the structure to the soil.
- Vertical loads or lateral forces from other parts of the structure to foundations.
1907.2 Nonstructural slabs-on-ground. Nonstructural slabs-on-ground shall be required to comply with Sections 1904.2, 1907.3 and 1907.4. Portions of the nonstructural slabs-on-ground used to resist uplift forces or overturning shall be designed in accordance with accepted engineering practice throughout the entire portion designated as dead load to resist uplift forces or overturning. 1907.3 Thickness. The thickness of concrete floor slabs supported directly on the ground shall be not less than 3 [1] / 2 inches (89 mm).
1907.4 Vapor retarder. A 6-mil (0.006 inch; 0.15 mm) polyethylene vapor retarder with joints lapped not less than 6 inches (152 mm) shall be placed between the base course or subgrade and the concrete floor slab, or other approved equivalent methods or materials shall be used to retard vapor transmission through the floor slab.
Exception: A vapor retarder is not required:
For detached structures accessory to occupancies in Group R-3, such as garages, utility buildings or other unheated facilities.
For unheated storage rooms having an area of less than 70 square feet (6.5 m [2] ) and carports attached to occupancies in Group R-3.
For buildings of other occupancies where migration of moisture through the slab from below will not be detrimental to the intended occupancy of the building.
For driveways, walks, patios and other flatwork that will not be enclosed at a later date.
Where approved based on local site conditions.
CRC § 6.895 Medium relevance — show source text
foundations and other concrete not exposed to the weather|2,500|2,500|2,500c| |Basement slabs and interior slabs on grade, except garage floor slabs|2,500|2,500|2,500c| |Basement walls, foundation walls, exterior walls and other vertical concrete work
exposed to the weather|2,500|3,000d|3,000d| |Porches, carport slabs and steps exposed to the weather, and garage floor slabs|2,500|3,000d, e, f|3,500d, e, f| |For SI: 1 pound per square inch = 6.895 kPa.
a. Strength at 28 days psi.
b. See Table R301.2 for weathering potential.
c. Concrete in these locations that is subject to freezing and thawing during construction shall be air-entrained concrete in accordance with Note d.
d. Concrete shall be air-entrained. Total air content (percent by volume of concrete) shall be not less than 5 percent or more than 7 percent.
e. See Section R402.2 for maximum cementitious materials content.
f. For garage floors with a steel-troweled finish, reduction of the total air content (percent by volume of concrete) to not less than 3 percent is permitted if the specified
compressive strength of the concrete is increased to not less than 4,000 psi.|For SI: 1 pound per square inch = 6.895 kPa.
a. Strength at 28 days psi.
b. See Table R301.2 for weathering potential.
c. Concrete in these locations that is subject to freezing and thawing during construction shall be air-entrained concrete in accordance with Note d.
d. Concrete shall be air-entrained. Total air content (percent by volume of concrete) shall be not less than 5 percent or more than 7 percent.
e. See Section R402.2 for maximum cementitious materials content.
f. For garage floors with a steel-troweled finish, reduction of the total air content (percent by volume of concrete) to not less than 3 percent is permitted if the specified
compressive strength of the concrete is increased to not less than 4,000 psi.|For SI: 1 pound per square inch = 6.895 kPa.
a. Strength at 28 days psi.
b. See Table R301.2 for weathering potential.
c. Concrete in these locations that is subject to freezing and thawing during construction shall be air-entrained concrete in accordance with Note d.
d. Concrete shall be air-entrained. Total air content (percent by volume of concrete) shall be not less than 5 percent or more than 7 percent.
e. See Section R402.2 for maximum cementitious materials content.
f. For garage floors with a steel-troweled finish, reduction of the total air content (percent by volume of concrete) to not less than 3 percent is permitted if the specified
compressive strength of the concrete is increased to not less than 4,000 psi.|For SI: 1 pound per square inch = 6.895 kPa.
a. Strength at 28 days psi.
b. See Table R301.2 for weathering potential.
c. Concrete in these locations that is subject to freezing and thawing during construction shall be air-entrained concrete in accordance with Note d.
d. Concrete shall be air-entrained.CRC § 304.8 Medium relevance — show source text
4 mm, 1 foot = 304.8 mm.
a. Mortar shall be Type M or S and masonry shall be laid in running bond. Ungrouted hollow masonry units are permitted except where otherwise indicated.
b. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
c. Unbalanced backfill height is the difference in height between the exterior finish ground level and the lower of the top of the concrete footing that supports the foundation
wall or the interior finish ground level. Where an interior concrete slab-on-grade is provided and is in contact with the interior surface of the foundation wall, measurement of
the unbalanced backfill height from the exterior finish ground level to the top of the interior concrete slab is permitted.
d. Solid indicates solid masonry unit; grout indicates grouted hollow units.
e. Wall construction shall be in accordance with Table R404.1.2.1(2), R404.1.2.1(3) or R404.1.2.1(4), or a design shall be provided.
f. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
a. Mortar shall be Type M or S and masonry shall be laid in running bond. Ungrouted hollow masonry units are permitted except where otherwise indicated.
b. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
c. Unbalanced backfill height is the difference in height between the exterior finish ground level and the lower of the top of the concrete footing that supports the foundation
wall or the interior finish ground level. Where an interior concrete slab-on-grade is provided and is in contact with the interior surface of the foundation wall, measurement of
the unbalanced backfill height from the exterior finish ground level to the top of the interior concrete slab is permitted.
d. Solid indicates solid masonry unit; grout indicates grouted hollow units.
e. Wall construction shall be in accordance with Table R404.1.2.1(2), R404.1.2.1(3) or R404.1.2.1(4), or a design shall be provided.
f. The use of this table shall be prohibited for soil classifications not shown.|For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
a. Mortar shall be Type M or S and masonry shall be laid in running bond. Ungrouted hollow masonry units are permitted except where otherwise indicated.
b. Soil classes are in accordance with the Unified Soil Classification System. Refer to Table R401.4.1(2).
c. Unbalanced backfill height is the difference in height between the exterior finish ground level and the lower of the top of the concrete footing that supports the foundation
wall or the interior finish ground level. Where an interior concrete slab-on-grade is provided and is in contact with the interior surface of the foundation wall, measurement of
the unbalanced backfill height from the exterior finish ground level to the top of the interior concrete slab is permitted.
d. Solid indicates solid masonry unit; grout indicates grouted hollow units.
e.CRC § 4.1 Medium relevance — show source text
APPENDIX BF-4 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
APPENDIX BF — PATIO COVERS
TABLE BF106.4.1(2)—ADJUSTMENT FACTOR FOR BUILDING HEIGHT AND EXPOSURE Col2 Col3 Col4 MEAN ROOF HEIGHT
(feet)** EXPOSURE** ** EXPOSURE** ** EXPOSURE** MEAN ROOF HEIGHT
(feet)B C D 15 1.00 1.21 1.47 20 1.00 1.29 1.55 25 1.00 1.35 1.61 30 1.00 1.40 1.66 35 1.05 1.45 1.70 40 1.09 1.49 1.74 45 1.12 1.53 1.78 50 1.16 1.56 1.81 55 1.19 1.59 1.84 60 1.22 1.62 1.87 For SI: 1 foot = 304.8 mm. For SI: 1 foot = 304.8 mm. For SI: 1 foot = 304.8 mm. For SI: 1 foot = 304.8 mm. BF106.4.2 Deflection limit. For members supporting screen surfaces only, the total load deflection shall not exceed l /60. Screen surfaces shall be permitted to include not more than 25-percent solid flexible finishes. BF106.4.3 Roof live load. The roof live load shall be not less than 10 psf (0.479 kN/m [2] ).
BF106.5 Footings. In areas with a frost line depth of zero, screen enclosures supported on a concrete slab-on-grade without footings shall conform to the provisions of Section R506, be not less than 3 [1] / 2 inches (89 mm) thick and the columns shall not support loads in excess of 750 pounds (3.36 kN) per column.
2025 CALIFORNIA RESIDENTIAL CODE APPENDIX BF-5
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
APPENDIX BF-6 2025 CALIFORNIA RESIDENTIAL CODE
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
CALIFORNIA RESIDENTIAL CODE – MATRIX ADOPTION TABLE
APPENDIX BG – SOUND TRANSMISSION
(Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.
Frequently asked questions
Do all slabs require a vapor retarder?
No. The CRC requires a 6‑mil vapor retarder where a base course does not exist or where the retarder is otherwise required by § R506.3.3, but lists exceptions (garages, small unheated storage < 70 ft², carports, exterior flatwork not likely to be enclosed, or building official approval) .
Can I use a thinner slab if I use higher‑strength concrete?
No. The CRC sets the minimum slab thickness at 3 1/2 in in § R506.1. Any design departures (including thinner slabs) must be engineered or follow the referenced standards (ACI 332 or PTI for PT slabs) as permitted by the code .
What if my site has expansive soils?
If expansive soils are present, the slab design must account for them. § R506.1 points to the foundation/soil provisions (for example § R403.1.8) — follow those sections or provide engineered design to address soil movement .
Is reinforcement mandatory in slabs on grade?
The CRC does not prescribe a single mandatory reinforcement pattern in § R506, but when reinforcement is provided it must be supported to the center to upper one‑third of the slab per § R506.3.4; detailed reinforcement design is generally done per ACI 332 or engineered design as referenced by § R506.1 .
How are concrete strength requirements determined?
Specified compressive strength for slabs is set in § R402.2; consult that section/table for the minimum f'c for your slab location (many interior slabs are 2,500 psi at 28 days, with special notes for garages and exposure) .
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