CRC · California Residential Code
How deep must footings be and how is frost protection provided?
For a homeowner: the code requires footings to be at least 12 inches deep, but if your area has freezing ground you must either dig deeper to the local frost line or use an approved frost‑protection method (insulation details for heated buildings or engineered solutions). Check your local frost‑line (Table R301.2) and the frost‑protection options in **§ R403.1.4.1** and **§ R403.3**, and confirm specifics with the building department.
Last reviewed: July 6, 2026
What the code requires — 2–4 sentences
Exterior footings must be placed at least 12 inches below the undisturbed ground surface, and where frost is a concern the footing depth or protection must meet the frost-protection methods listed in § R403.1.4 and § R403.1.4.1. The code says footings must either be extended below the local frost line, be constructed as frost-protected shallow foundations (FPSF) per § R403.3, comply with ASCE 32, or be erected on solid rock; footings shall not bear on frozen soil unless the frozen condition is permanent. See § R403.1.4 and § R403.1.4.1 for the controlling language.
The single most important rule: exterior footings must be at least 12 inches deep below undisturbed ground, and when frost can damage foundations you must either go deeper (below the local frost line) or use an approved frost-protection method. § R403.1.4 and § R403.1.4.1 are the controlling provisions.
Requirements in detail
Minimum exterior footing depth
- Minimum depth: 12 inches below undisturbed ground surface (the baseline). § R403.1.4.
When frost protection applies
Where frost can penetrate and cause damage, the footing must be protected by one or more of the methods listed in § R403.1.4.1:
- Extend the footing below the frost line for the locality (see Table R301.2 for the frost-line depth used locally). § R403.1.4.1.
- Construct in accordance with § R403.3 (frost-protected shallow foundation / insulation scheme). § R403.1.4.1 and § R403.3.
- Construct in accordance with ASCE 32 (engineering standard for frost protection). § R403.1.4.1.
- Erect the foundation on solid rock. § R403.1.4.1.
Footings must not bear on frozen soil unless the frozen condition is permanent. § R403.1.4.1.
Deck footings
- Deck footings have the same 12‑inch minimum and must be frost-protected where applicable; see § R507.3 and § R403.1.4.1 for the same methods of protection. § R507.3 references the same frost-protection methods.
Table — decision‑relevant minimums and options
| Item | Decision-relevant dimension / value | Code Reference |
|---|---|---|
| Baseline min. exterior footing depth | 12 in. below undisturbed ground | § R403.1.4 |
| Frost protection — option 1 | Extend footing below local frost line (value from Table R301.2 / local jurisdiction) | § R403.1.4.1; see Table R301.2 |
| Frost protection — option 2 | Use frost‑protected shallow foundation per insulation detail and minimum D and R‑values in Table R403.3(1) | § R403.1.4.1 and § R403.3; see Table R403.3(1) for D and R values |
| Frost protection — option 3 | Construct per ASCE 32 (engineered frost protection) | § R403.1.4.1 |
| Frost protection — option 4 | Erect on solid rock | § R403.1.4.1 |
| Deck footings min. & frost | 12 in. min.; protect from frost using same options when required | § R507.3 and § R403.1.4.1 |
Note: Table R403.3(1) contains numeric minimum footing depths and insulation R‑values for frost‑protected shallow foundations; those numeric values and the locality frost‑line depths are shown in the full code tables and by the local jurisdiction. Consult Table R403.3(1) and Table R301.2 for the specific numbers.
Exceptions & special cases
- Small free‑standing accessory structures may be exempt from frost protection: light‑frame accessory buildings ≤ 600 ft² (eave height ≤ 10 ft) and other construction ≤ 400 ft² (eave height ≤ 10 ft) are exempt per the exceptions in § R403.1.4.1.
- Frost‑protected shallow foundations (FPSF) under § R403.3 are allowed only for buildings where the monthly mean interior temperature is maintained at not less than 64°F (18°C). FPSF are not permitted for unheated spaces (porches, garages, unheated utility rooms) or for foundations attached to basements/crawl spaces that are not heated to that 64°F threshold. Materials used below grade for insulation must comply with ASTM C578. § R403.3.
- Where a jurisdiction adopts and fills in Table R301.2, the local frost‑line depth controls — the code anticipates local adoption/fill‑in of the frost depth. Check your local Table R301.2 or with the building official.
- Footings may not rest on temporarily frozen soils; they must bear on unfrozen competent soils or rock unless the frozen state is permanent. § R403.1.4.1.
Common mistakes
- Assuming 12 inches is always enough — 12 inches is the baseline minimum, but if the local frost line is deeper, you must meet the deeper frost‑line depth or use an approved frost‑protection method per § R403.1.4.1.
- Trying to use frost‑protected shallow foundation details for unheated spaces (garage, porch) — § R403.3 forbids EPSF use for unheated spaces unless those spaces are maintained at 64°F (18°C).
- Not checking the local frost‑line values in Table R301.2 or with the building official — frost depths vary by locality and may be filled in by the jurisdiction.
- Bearing a footing on frozen soil temporarily present during construction — the code prohibits this unless frozen condition is permanent. § R403.1.4.1.
- Overlooking deck‑footing special rules — deck footings have their own subsection § R507.3, which refers back to the same frost‑protection methods.
Worked example — applying the rule with numbers (illustrative)
Scenario (illustrative only — check local tables): you are building an exterior foundation wall in a locality where the local building department (Table R301.2) indicates a frost line of 36 inches.
- Baseline: code requires exterior footings to be at least 12 in. below undisturbed ground per § R403.1.4.
- Frost check: because the local frost line is 36 in., you must protect against frost. The simplest prescriptive method is to extend the footing to at least 36 in. below undisturbed ground, i.e., the footing depth becomes 36 in. (because the deeper frost‑line requirement governs). This meets § R403.1.4.1 option (1).
- Alternative: instead of digging to 36 in., you could design a frost‑protected shallow foundation per § R403.3 (using the insulation layout and the minimum D and R‑values shown in Table R403.3(1)); that may allow shallower footings if the required insulation and detail are provided and the structure is heated to the required interior temperature. See § R403.3 and Table R403.3(1).
Note: the numeric frost‑line depth (36 in. in this example) must come from Table R301.2 or the local building official — the code text requires you follow the local frost depth or use the alternative methods in § R403.1.4.1.
Related provisions
- § R403.1.4 — Minimum depth of exterior footings (12 in. baseline).
- § R403.1.4.1 — Frost protection methods and exceptions.
- § R403.3 — Frost‑protected shallow foundations (FPSF) and required insulation/table.
- § R507.3 — Deck footings: minimum depth and frost protection where applicable.
- Table R301.2 — Local frost‑line depths and other locality parameters (refer to your adopted local table).
- Table R403.3(1) — Minimum footing depth (D) and insulation R‑values for FPSF (see the table in § R403.3).
Code references
Grounded in the retrieved California Residential Code — click a citation to read the verbatim passage:
CRC § 1.3.5.4 High relevance — show source text
R403.1.3.5.4 Lap splices. Vertical and horizontal reinforcement shall be the longest lengths practical. Where splices are necessary in reinforcement, the length of lap splice shall be in accordance with Table R608.5.4(1) and Figure R608.5.4(1). The maximum gap between noncontact parallel bars at a lap splice shall not exceed the smaller of one-fifth the required lap length and 6 inches (152 mm) [see Figure R608.5.4(1)].
R403.1.3.6 Isolated concrete footings. In detached one- and two-family dwellings that are three stories or less in height and constructed with stud bearing walls, isolated plain concrete footings supporting columns or pedestals are permitted.
R403.1.4 Minimum depth. Exterior footings shall be placed not less than 12 inches (305 mm) below the undisturbed ground surface. Where applicable, the depth of footings shall also conform to Section R403.1.4.1. Deck footings shall be in accordance with Section R507.3.
R403.1.4.1 Frost protection. Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
Extended below the frost line specified in Table R301.2.
Constructed in accordance with Section R403.3.
Constructed in accordance with ASCE 32.
Erected on solid rock.
Footings shall not bear on frozen soil unless the frozen condition is permanent.
Exceptions:
- Protection of free-standing accessory structures with an area of 600 square feet (56 m [2] ) or less, of light-frame construction, with an eave height of 10 feet (3048 mm) or less shall not be required.
- Protection of free-standing accessory structures with an area of 400 square feet (37 m [2] ) or less, of other than lightframe construction, with an eave height of 10 feet (3048 mm) or less shall not be required.
4-14 2025 CALIFORNIA RESIDENTIAL CODE
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FOUNDATIONS
R403.1.5 Slope. The top surface of footings shall be level. The bottom surface of footings shall not have a slope exceeding 1 unit vertical in 10 units horizontal (10-percent slope). Footings shall be stepped where it is necessary to change the elevation of the top surface of the footings or where the slope of the bottom surface of the footings will exceed 1 unit vertical in 10 units horizontal (10percent slope).
R403.1.6 Foundation anchorage. Wood sill plates and wood walls supported directly on continuous foundations shall be anchored to the foundation in accordance with this section.
Cold-formed steel framing shall be anchored directly to the foundation or fastened to wood sill plates in accordance with Section R505.3.1 or R603.3.1, as applicable. Wood sill plates supporting cold-formed steel framing shall be anchored to the foundation in accordance with this section.
CRC § 4-22 High relevance — show source text
4-22 2025 CALIFORNIA RESIDENTIAL CODE
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FOUNDATIONS
FIGURE R403.5(1)—CRUSHED STONE FOOTINGS FOR CAST-IN-PLACE CONCRETE FOUNDATIONS IN SEISMIC DESIGN CATEGORIES A, B, AND C AND WIND EXPOSURE CATEGORIES B, C, AND D: CAST-IN-PLACE CONCRETE FOUNDATION WALL WITH WOOD CRIPPLE WALL
MIN. CLEARANCE PER
SECTIONS R404.1.6 AND
R304.1 TYP.
TOP OF FOOTING MIN. 4 IN.
BELOW UNDISTURBED GROUND
SURFACE
12 IN. MIN. FOOTING DEPTH PER
SECTION R403.1.4
GREATER DEPTH FOR FROST
PROTECTION WHERE
APPLIABLE PER SECTION
R403.1.4.1
NOT TO SCALE
For SI: 1 inch = 25.4 mm, 1 foot = 304.5 mm.
CAST-IN-PLACE CONCRETE
FOUNDATION WALL PER TABLE
R403.5 W/ #4 HORIZONTAL REBAR @ 18" OC. MIN.
PLACE ONE #4 REBAR W/ 3" CLEAR
FROM BOTTOM AND ONE #4 REBAR
W/ 2" CLR FROM TOP
TOP OF FOOTING MIN. 4 IN.
BELOW UNDISTURBED GROUND
SURFACE
12 IN. MIN. FOOTING DEPTH PER
SECTION R403.1.4
AREA OF EXTENDED CRUSHED
STONE FOOTING DEPTH AT
WIDTH 'W' TO BELOW FROST
LINE WHERE APPLICABLE
NOT TO SCALE
For SI: 1 inch = 25.4 mm, 1 foot = 304.5 mm.
2025 CALIFORNIA RESIDENTIAL CODE 4-23
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FOUNDATIONS
FIGURE R403.5(3)—CRUSHED STONE FOOTINGS FOR CAST-IN-PLACE CONCRETE FOUNDATIONS IN SEISMIC DESIGN CATEGORIES A, B, AND C AND WIND EXPOSURE CATEGORIES B, C, AND D: CONCRETE SLAB-ON-GROUND WITH TURNED DOWN FOUNDATION
SILL PLATE AND ANCHORAGE
PER SECTION R403.5 ANCHORS
WITH 7" MIN. EMBEDMENT
MIN. CLEARANCE PER
SECTIONS R404.1.6 AND
R304.1 TYP.
TOP OF FOOTING MIN. 4 IN.
BELOW UNDISTURBED GROUND
SURFACE
12 IN. MIN. FOOTING DEPTH PER
SECTION R403.1.4
GREATER DEPTH FOR FROST
PROTECTION WHERE
APPLICABLE PER SECTION
R403.1.4.1
NOT TO SCALE
For SI: 1 inch = 25.4 mm, 1 foot = 304.5 mm.
|TABLE R403.5—MINIMUM CAST-IN-PLACE CONCRETE FOUNDATION WALL
DIMENSIONS,CRC § 5.1 High relevance — show source text
1809 A .3 Stepped footings. The top surface of footings shall be level. The bottom surface of footings shall be permitted to have a slope not exceeding 1 unit vertical in 10 units horizontal (10-percent slope). Footings shall be stepped where it is necessary to change the elevation of the top surface of the footing or where the surface of the ground slopes more than 1 unit vertical in 10 units horizontal (10-percent slope).
Individual steps in continuous footings shall not exceed 18 inches (457 mm) in height and the slope of a series of such steps shall not exceed 1 unit vertical to 2 units horizontal (50 percent slope) unless otherwise recommended by a geotechnical report. The steps shall be detailed on the drawings. The local effects due to the discontinuity of the steps shall be considered in the design of the foundation.
1809 A .4 Depth and width of footings. The minimum depth of footings below the undisturbed ground surface shall be 12 inches (305 mm). Where applicable, the requirements of Section 1809 A .5 shall be satisfied. The minimum width of footings shall be 12 inches (305 mm).
1809 A .5 Frost protection. Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
- Extending below the frost line of the locality.
- Constructing in accordance with ASCE 32.
- Erecting on solid rock.
Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:
Assigned to Risk Category I.
Area of 600 square feet (56 m [2] ) or less for light-frame construction or 400 square feet (37 m [2] ) or less for other than lightframe construction.
Eave height of 10 feet (3048 mm) or less.
Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.
1809 A .5.1 Frost protection at required exits. Frost protection shall be provided at exterior landings for all required exits with outward-swinging doors. Frost protection shall only be required to the extent necessary to ensure the unobstructed opening of the required exit doors.
1809 A .6 Location of footings. Footings on granular soil shall be so located that the line drawn between the lower edges of adjacent footings shall not have a slope steeper than 30 degrees (0.52 rad) with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported in an approved manner or a greater slope has been properly established by engineering analysis.
1809 A .7 Prescriptive footings for light-frame construction. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.
1809 A .8 Plain concrete footings. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.
1809 A .9 Masonry-unit footings. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.
1809 A .10 Pier and curtain wall foundations. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.
CRC § 1.3.5 High relevance — show source text
R403.1.3.5 Reinforcement. Footing and stem wall reinforcement shall comply with Sections R403.1.3.5.1 through R403.1.3.5.4.
R403.1.3.5.1 Steel reinforcement. Steel reinforcement shall comply with the requirements of ASTM A615, A706M or A996M. ASTM A996M bars produced from rail steel shall be Type R. The minimum yield strength of reinforcing steel shall be 40,000 psi (Grade 40) (276 MPa).
R403.1.3.5.2 Location of reinforcement in wall. The center of vertical reinforcement in stem walls shall be located at the centerline of the wall. Horizontal and vertical reinforcement shall be located in footings and stem walls to provide the minimum cover required by Section R403.1.3.5.3.
R403.1.3.5.3 Support and cover. Reinforcement shall be secured in the proper location in the forms with tie wire or other bar support system to prevent displacement during the concrete placement operation. Steel reinforcement in concrete cast against the earth shall have a minimum cover of 3 inches (75 mm). Minimum cover for reinforcement in concrete cast in removable forms that will be exposed to the earth or weather shall be 1 [1] / 2 inches (38 mm) for No. 5 bars and smaller, and 2 inches (50 mm) for No. 6 bars and larger. For concrete cast in removable forms that will not be exposed to the earth or weather, and for concrete cast in stay-in-place forms, minimum cover shall be [3] / 4 inch (19 mm).
R403.1.3.5.4 Lap splices. Vertical and horizontal reinforcement shall be the longest lengths practical. Where splices are necessary in reinforcement, the length of lap splice shall be in accordance with Table R608.5.4(1) and Figure R608.5.4(1). The maximum gap between noncontact parallel bars at a lap splice shall not exceed the smaller of one-fifth the required lap length and 6 inches (152 mm) [see Figure R608.5.4(1)].
R403.1.3.6 Isolated concrete footings. In detached one- and two-family dwellings that are three stories or less in height and constructed with stud bearing walls, isolated plain concrete footings supporting columns or pedestals are permitted.
R403.1.4 Minimum depth. Exterior footings shall be placed not less than 12 inches (305 mm) below the undisturbed ground surface. Where applicable, the depth of footings shall also conform to Section R403.1.4.1. Deck footings shall be in accordance with Section R507.3.
R403.1.4.1 Frost protection. Except where otherwise protected from frost, foundation walls, piers and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
Extended below the frost line specified in Table R301.2.
Constructed in accordance with Section R403.3.
Constructed in accordance with ASCE 32.
Erected on solid rock.
Footings shall not bear on frozen soil unless the frozen condition is permanent.
CRC § 25.4 High relevance — show source text
Interpolation permitted, extrapolation not permitted.
b. Based on highest load case: Dead + Live or Dead + Snow.
c. Footing dimensions shall allow complete bearing of the post.
d. If the support is a brick or CMU pier, the footing shall have a minimum 2-inch projection on all sides.
e. Area, in square feet, of deck surface supported by post and footings.|For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa.
a. Interpolation permitted, extrapolation not permitted.
b. Based on highest load case: Dead + Live or Dead + Snow.
c. Footing dimensions shall allow complete bearing of the post.
d. If the support is a brick or CMU pier, the footing shall have a minimum 2-inch projection on all sides.
e. Area, in square feet, of deck surface supported by post and footings.|For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa.
a. Interpolation permitted, extrapolation not permitted.
b. Based on highest load case: Dead + Live or Dead + Snow.
c. Footing dimensions shall allow complete bearing of the post.
d. If the support is a brick or CMU pier, the footing shall have a minimum 2-inch projection on all sides.
e. Area, in square feet, of deck surface supported by post and footings.|For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa.
a. Interpolation permitted, extrapolation not permitted.
b. Based on highest load case: Dead + Live or Dead + Snow.
c. Footing dimensions shall allow complete bearing of the post.
d. If the support is a brick or CMU pier, the footing shall have a minimum 2-inch projection on all sides.
e. Area, in square feet, of deck surface supported by post and footings.|For SI: 1 inch = 25.4 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa.
a. Interpolation permitted, extrapolation not permitted.
b. Based on highest load case: Dead + Live or Dead + Snow.
c. Footing dimensions shall allow complete bearing of the post.
d. If the support is a brick or CMU pier, the footing shall have a minimum 2-inch projection on all sides.
e. Area, in square feet, of deck surface supported by post and footings.|R507.3.2 Minimum depth. Deck footings shall be placed not less than 12 inches (305 mm) below the undisturbed ground surface.
R507.3.3 Frost protection. Where decks are attached to a frost-protected structure, deck footings shall be protected from frost by one or more of the following methods:
- Extending below the frost line specified in Table R301.2.
- Erecting on solid rock.
- Other approved methods of frost protection.
2025 CALIFORNIA RESIDENTIAL CODE 5-29
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FLOORS
CRC § 1809.5 High relevance — show source text
1809.5 Frost protection. Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
- Extending below the frost line of the locality.
- Constructing in accordance with ASCE 32.
- Erecting on solid rock.
Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:
Assigned to Risk Category I.
Area of 600 square feet (56 m [2] ) or less for light-frame construction or 400 square feet (37 m [2] ) or less for other than lightframe construction.
Eave height of 10 feet (3048 mm) or less.
Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.
1809.5.1 Frost protection at required exits. Frost protection shall be provided at exterior landings for all required exits with outward-swinging doors. Frost protection shall only be required to the extent necessary to ensure the unobstructed opening of the required exit doors.
1809.6 Location of footings. Footings on granular soil shall be so located that the line drawn between the lower edges of adjacent footings shall not have a slope steeper than 30 degrees (0.52 rad) with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported in an approved manner or a greater slope has been properly established by engineering analysis.
1809.7 Prescriptive footings for light-frame construction. [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Where a specific design is not provided, concrete or masonry-unit footings supporting walls of light-frame construction shall be permitted to be designed in accordance with Table 1809.7.
TABLE 1809.7—PRESCRIPTIVE FOOTINGS SUPPORTING WALLS OF LIGHT-FRAME CONSTRUCTIONa, b, c, d, e Col2 Col3 NUMBER OF FLOORS SUPPORTED BY THE FOOTINGf WIDTH OF FOOTING (inches) THICKNESS OF FOOTING (inches) 1 12 6 2 15 6 3 18 8g For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
a. Depth of footings shall be in accordance with Section 1809.4.
b. The ground under the floor shall be permitted to be excavated to the elevation of the top of the footing.
c. Interior stud-bearing walls shall be permitted to be supported by isolated footings. The footing width and length shall be twice the width shown in this table, and footings
shall be spaced not more than 6 feet on center.
d. See Section 1905 for additional requirements for concrete footings of structures assigned to Seismic Design Category C, D, E or F.
e. For thickness of foundation walls, see Section 1807.1.6.
f. Footings shall be permitted to support a roof in addition to the stipulated number of floors. Footings supporting roof only shall be as required for supporting one floor.
g. Plain concrete footings for Group R-3 occupancies shall be permitted to be 6 inches thick.For SI: 1 inch = 25.4 mm, 1 foot = 304.8 mm.
a.California Residential Code High 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.CRC § 1809.2 High relevance — show source text
1809.2 Supporting soils. Shallow foundations shall be built on undisturbed soil, compacted fill material or controlled low-strength material (CLSM). Compacted fill material shall be placed in accordance with Section 1804.6. CLSM shall be placed in accordance with Section 1804.7.
1809.3 Stepped footings. The top surface of footings shall be level. The bottom surface of footings shall be permitted to have a slope not exceeding 1 unit vertical in 10 units horizontal (10-percent slope). Footings shall be stepped where it is necessary to change the elevation of the top surface of the footing or where the surface of the ground slopes more than 1 unit vertical in 10 units horizontal (10-percent slope).
[OSHPD 1R, 2 & 5] Individual steps in continuous footings shall not exceed 18 inches (457 mm) in height and the slope of a series of such steps shall not exceed 1 unit vertical to 2 units horizontal (50-percent slope) unless otherwise recommended by a geotechnical report.
18-18 2025 CALIFORNIA BUILDING CODE
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SOILS AND FOUNDATIONS
The steps shall be detailed on the drawings. The local effects due to the discontinuity of the steps shall be considered in the design of the foundation.
1809.4 Depth and width of footings. The minimum depth of footings below the undisturbed ground surface shall be 12 inches (305 mm). Where applicable, the requirements of Section 1809.5 shall be satisfied. The minimum width of footings shall be 12 inches (305 mm).
1809.5 Frost protection. Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:
- Extending below the frost line of the locality.
- Constructing in accordance with ASCE 32.
- Erecting on solid rock.
Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:
Assigned to Risk Category I.
Area of 600 square feet (56 m [2] ) or less for light-frame construction or 400 square feet (37 m [2] ) or less for other than lightframe construction.
Eave height of 10 feet (3048 mm) or less.
Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.
1809.5.1 Frost protection at required exits. Frost protection shall be provided at exterior landings for all required exits with outward-swinging doors. Frost protection shall only be required to the extent necessary to ensure the unobstructed opening of the required exit doors.
1809.6 Location of footings. Footings on granular soil shall be so located that the line drawn between the lower edges of adjacent footings shall not have a slope steeper than 30 degrees (0.52 rad) with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported in an approved manner or a greater slope has been properly established by engineering analysis.
CRC § 1.7.3 High relevance — show source text
R403.1.7.3 Foundation elevation. On graded sites, the top of any exterior foundation shall extend above the elevation of the street gutter at point of discharge or the inlet of an approved drainage device not less than 12 inches (305 mm) plus 2 percent. Alternate elevations are permitted subject to the approval of the building official, provided that it can be demonstrated that required drainage to the point of discharge and away from the structure is provided at all locations on the site.
R403.1.7.4 Alternate setbacks and clearances. Alternate setbacks and clearances are permitted, subject to the approval of the building official. The building official is permitted to require an investigation and recommendation of a qualified engineer to demonstrate that the intent of this section has been satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.
R403.1.8 Foundations on expansive soils. Foundation and floor slabs for buildings located on expansive soils shall be designed in accordance with Section 1808.6 of the California Building Code .
Exception: Slab-on-ground and other foundation systems that have performed adequately in soil conditions similar to those encountered at the building site are permitted subject to the approval of the building official.
R403.1.8.1 Expansive soils classifications. Soils meeting all of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:
Plasticity Index (PI) of 15 or greater, determined in accordance with ASTM D4318.
More than 10 percent of the soil particles pass a No. 200 sieve (75 μ m), determined in accordance with ASTM D422.
More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D422.
Expansion Index greater than 20, determined in accordance with ASTM D4829.
R403.2 Footings for wood foundations. Footings for wood foundations shall be in accordance with Figures R403.1(2) and R403.1(3). Gravel shall be washed and well graded. The maximum size stone shall not exceed [3] / 4 inch (19.1 mm). Gravel shall be free from organic, clayey or silty soils. Sand shall be coarse, not smaller than [1] / 16 -inch (1.6 mm) grains and shall be free from organic, clayey or silty soils. Crushed stone shall have a maximum size of [1] / 2 inch (12.7 mm).
R403.3 Frost-protected shallow foundations. For buildings where the monthly mean temperature of the building is maintained at not less than 64°F (18°C), footings are not required to extend below the frost line where protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).
Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C578.
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CRC § 2.1.4. High relevance — show source text
Where weathering requires a higher strength concrete or grade of masonry than necessary to satisfy the structural requirements of this code, the frost line depth strength required
for weathering shall govern. The weathering column shall be filled in with the weathering index, “negligible,” “moderate” or “severe” for concrete as determined from Figure
R301.2(1). The grade of masonry units shall be determined from ASTM C34, ASTM C55, ASTM C62, ASTM C73, ASTM C90, ASTM C129, ASTM C145, ASTM C216 or ASTM C652.
b. Where the frost line depth requires deeper footings than indicated in Figure R403.1(1), the frost line depth strength required for weathering shall govern. The jurisdiction shall
fill in the frost line depth column with the minimum depth of footing below finish grade.
c. The jurisdiction shall fill in this part of the table to indicate the need for protection depending on whether there has been a history of local subterranean termite damage.
d. The jurisdiction shall fill in this part of the table with the wind speed from the ultimate design wind speeds map [Figure R301.2(2)]. Wind exposure category shall be determined
on a site-specific basis in accordance with Section R301.2.1.4.
e. The jurisdiction shall fill in this section of the table to establish the design criteria using Table 10A from ACCA Manual J or established criteria determined by the jurisdiction.
f. The jurisdiction shall fill in this part of the table with the seismic design category determined from Section R301.2.2.1.
g. The jurisdiction shall fill in this part of the table with: the date of the jurisdiction’s entry into the National Flood Insurance Program (date of adoption of the first code or ordi-
nance for management of flood hazard areas); and the title and date of the currently effective Flood Insurance Study or other flood hazard study and maps adopted by the
authority having jurisdiction, as amended.
h. In accordance with Sections R905.1.2, R905.4.3.1, R905.5.3.1, R905.6.3.1, R905.7.3.1 and R905.8.3.1, where there has been a history of local damage from the effects of ice
damming, the jurisdiction shall fill in this part of the table with “YES.” Otherwise, the jurisdiction shall fill in this part of the table with “NO.”
i. The jurisdiction shall fill in this part of the table with the 100-year return period air freezing index (BF-days) from Figure R403.3(2) or from the 100-year (99 percent) value on the
National Climatic Data Center data table “Air Freezing Index-USA Method (Base 32°F).”
j. The jurisdiction shall fill in this part of the table with the mean annual temperature from the National Climatic Data Center data table “Air Freezing Index-USA Method (Base 32°F).”
k. In accordance with Section R301.2.1.5, where there is local historical data documenting structural damage to buildings due to topographic wind speed-up effects, the jurisdic-
tion shall fill in this part of the table with “YES.” Otherwise, the jurisdiction shall indicate “NO” in this part of the table.
l. In accordance with Figure R301.2(2), where there is local historical data documenting unusual wind conditions, the jurisdiction shall fill in this part of the table with “YES” and
identify any specific requirements.CRC § 19.1 Medium relevance — show source text
- Expansion Index greater than 20, determined in accordance with ASTM D4829.
R403.2 Footings for wood foundations. Footings for wood foundations shall be in accordance with Figures R403.1(2) and R403.1(3). Gravel shall be washed and well graded. The maximum size stone shall not exceed [3] / 4 inch (19.1 mm). Gravel shall be free from organic, clayey or silty soils. Sand shall be coarse, not smaller than [1] / 16 -inch (1.6 mm) grains and shall be free from organic, clayey or silty soils. Crushed stone shall have a maximum size of [1] / 2 inch (12.7 mm).
R403.3 Frost-protected shallow foundations. For buildings where the monthly mean temperature of the building is maintained at not less than 64°F (18°C), footings are not required to extend below the frost line where protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).
Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C578.
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on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FOUNDATIONS
FIGURE R403.3(1)—INSULATION PLACEMENT FOR FROST-PROTECTED FOOTINGS IN HEATED BUILDINGS
INSULATION DETAIL
SLAB-ON-GROUND FOUNDATION FLOOR
R403.3.3
HORIZONTAL INSULATION PLAN
For SI: 1 inch = 25.4 mm.
a. See Table R403.3(1) for required dimensions and R -values for vertical and horizontal insulation and minimum footing depth.
2025 CALIFORNIA RESIDENTIAL CODE 4-17
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FOUNDATIONS
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on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.
FOUNDATIONS
TABLE R403.3(1)—MINIMUM FOOTING DEPTH AND
INSULATION REQUIREMENTS FOR FROST-PROTECTED FOOTINGS IN HEATED BUILDINGSaCol2 Col3 Col4 Col5 Col6 Col7 Col8 ** AIR-
FREEZING
INDEX0
(°F days)b**** MINIMUM**
FOOTING DEPTH,
D (inches)** VERTICAL**
INSULATION
R-VALUEc, d** HORIZONTAL**
INSULATIONR-VALUEc,** HORIZONTAL**
INSULATION**R-VALUEc,
Frequently asked questions
What is the absolute minimum depth I can dig for an exterior footing?
The absolute code baseline is 12 inches below undisturbed ground per § R403.1.4. If frost is a concern, you must follow § R403.1.4.1 and either go deeper to the local frost line or use an approved frost‑protection method.
How do I find my local frost‑line depth?
The code refers to Table R301.2 for frost‑line depth values and anticipates jurisdictions will fill in the table; contact your local building department or check the adopted code tables for your locality. § R403.1.4.1 points to the local frost line.
Can I avoid digging deep by insulating the foundation?
Yes—if the building is heated (monthly mean ≥ 64°F / 18°C) you may use the frost‑protected shallow foundation details in § R403.3 (insulation placement and R‑values per Table R403.3(1)). FPSF is not allowed for unheated spaces or attachments that are unheated.
Are small sheds exempt from frost protection?
Some small free‑standing accessory structures are exempt: light‑frame ≤ 600 ft² (eave height ≤ 10 ft) or other construction ≤ 400 ft² (eave height ≤ 10 ft), per the exceptions in § R403.1.4.1. Confirm local interpretation with building official.
Can I place a footing on frozen ground during construction?
No — footings shall not bear on frozen soil unless the frozen condition is permanent; the code requires footing bearing on unfrozen competent soils or rock. § R403.1.4.1.
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