CBC · California Building Code

What are the rules for retaining walls, foundation walls and embedded posts/poles?

In plain terms: foundation and retaining walls must be designed for soil lateral forces (see § 1610) and retaining walls must meet minimum safety factors (usually 1.5, 1.1 with earthquake loads) and guard rules when a walkway is close to a drop; posts and poles set in the ground must follow the embedment formulas and backfill rules in § 1807.3 (including treatment for wood and minimum concrete/backfill specs). All designs that rely on soil strength should use § 1806 tabular values or a geotechnical report per § 1803.

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Last reviewed: July 5, 2026

What the code requires — 2-4 sentences

The California Building Code requires foundation walls to be designed for the lateral soil loads set by Section 1610 and for retaining walls to be designed for stability against overturning, sliding, excessive foundation pressure and water uplift (§ 1807.1, § 1807.2). Retaining walls must meet minimum safety factors against sliding and overturning (normally 1.5; 1.1 when earthquake loads are included) per § 1807.2.3. Designs for posts or poles embedded in earth (including required embedment depth to resist lateral loads and acceptable backfill) are governed by § 1807.3 and the formulas and limits in that section.

Requirements in detail

Foundation walls (§ 1807.1)

Design basis: Foundation walls must be designed for lateral soil loads as set forth in Section 1610; foundations that support foundation walls must comply with § 1808. Measurement of “unbalanced backfill height” is defined in § 1807.1.2 and affects design. Prescriptive minimum wall widths and other prescriptive provisions for concrete and masonry foundation walls appear at § 1807.1.6 (including allowances for 8‑inch and 10‑inch nominal foundation widths in limited circumstances).

Key points:

Always design foundation walls to the lateral soil load criteria in § 1610 (§ 1807.1.1).
Unbalanced backfill height (how much higher the outside grade is vs. the footing/top of slab) is defined and used for design (§ 1807.1.2).
Prescriptive thickness rules exist (see § 1807.1.6); consult those tables or design per Chapter 19/21 for concrete/masonry walls.

Retaining walls (§ 1807.2 and § 1807.2.3)

General requirement: Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift (§ 1807.2.1). Lateral soil loads shall be determined in accordance with § 1610 or by a geotechnical investigation where required (§ 1807.2.2).
Safety factor (decision-critical): Retaining walls must be designed to produce a minimum safety factor of 1.5 against sliding and overturning. When earthquake loads are included, the minimum safety factor is reduced to 1.1. The code directs use of 0.7× nominal earthquake loads, 1.0× other nominal loads and investigation(s) with one or more variable loads set to zero when evaluating the safety factor (§ 1807.2.3).
Guards: Where a retaining wall is within 36 inches (914 mm) of a walking surface and the vertical drop to the lower grade is more than 30 inches (762 mm) at a point within 36 inches horizontally, a guard is required (guards must comply with Section 1607.9; height/opening limits per Sections 1015.3 and 1015.4). Exception: guards not required at retaining walls not accessible to the public (§ 1807.2.5 and subsections).

Embedded posts and poles (§ 1807.3)

Scope: Designs for posts or poles embedded in earth (as columns) to resist axial and lateral loads must follow §§ 1807.3.1–1807.3.3 or ASABE EP 486.3 (§ 1807.3).
Limitations:
- Frictional resistance for structural walls and slabs on silts/clays shall be limited to one‑half of the normal force imposed by the weight of the footing or slab (§ 1807.3.1).
- Posts embedded in earth shall not be used to provide lateral support for structural or non‑structural finishes (e.g., plaster, masonry, concrete) unless bracing is provided to develop the required limited deflection (§ 1807.3.1).
- Wood poles must be preservative‑treated in accordance with AWPA U1 (Use Category 4B) for sawn and round timber (§ 1807.3.1).
Embedment depth to resist lateral loads:
- Nonconstrained condition (no lateral constraint at ground surface or above): use Equation 18‑1 in § 1807.3.2.1 to compute embedment depth d, where A = 2.34 P / (S1 b), b = post diameter (ft), h = distance from ground to point of applied lateral force P, and S1 is the allowable lateral soil‑bearing pressure as set out in § 1806 (based on one‑third the depth of embedment). The depth used for computing lateral pressure is limited to 12 ft in the equation (§ 1807.3.2.1).
- Constrained conditions: § 1807.3.2.2 provides alternate equations for constrained cases (rigid pavement or slab at grade).
Backfill around columns not embedded in poured footings (§ 1807.3.3):
1. Concrete backfill of at least 2,000 psi; hole not less than 4 in larger than column diameter/diagonal at bottom.
2. Clean sand, compacted in layers not more than 8 in. deep.
3. Controlled low‑strength material (CLSM).

Decision‑relevant quick reference table

Item	Value/Dimension	When it applies / significance	Code Reference
Retaining wall safety factor (sliding & overturning)	1.5 (normal)	Minimum SF required for design stability	§ 1807.2.3 —
Retaining wall safety factor with earthquake loads	1.1 (min with earthquake loads included)	Lowered minimum when earthquake loads are considered	§ 1807.2.3 —
Guard trigger distance (horizontal)	36 in (914 mm)	If walking surface within this distance and vertical drop > 30 in, guard required	§ 1807.2.5.1 —
Guard trigger drop (vertical)	30 in (762 mm)	See guard trigger condition above	§ 1807.2.5.1 —
Max depth used for computing lateral pressure in embedment eqn	12 ft (3658 mm)	Equation 18‑1 limits depth used for lateral pressure computation	§ 1807.3.2.1 —
Backfill concrete strength around post	2,000 psi (13.8 MPa)	Option for backfilling annular space around columns not in poured footing	§ 1807.3.3 —
Required clear annular space for concrete backfill	≥ 4 in (102 mm)	Hole must be at least this much larger than column at bottom	§ 1807.3.3 —
Sand backfill compaction layer thickness	≤ 8 in (203 mm) per lift	Maximum layer depth for tamping/compaction	§ 1807.3.3 —
Wood pole treatment standard	AWPA U1 (Use Category 4B)	Required preservative treatment for sawn and round timber poles	§ 1807.3.1 —
Design lateral soil loads for foundation/retaining walls	See § 1610 / geotechnical investigation	Foundation/retaining walls must be designed per § 1610 or geotech report	§ 1807.1.1, § 1807.2.2 —

Note: numeric tabular values for allowable lateral soil‑bearing pressures (S1) and presumptive tabulated soil values are found in Section 1806 and its tables. These specific table numbers and numeric values were not included in the retrieved snippets; obtain S1 from Table 1806.2 or from a geotechnical investigation per § 1803 as required.

Exceptions & special cases

Earthquake loading: when earthquake loads are included in the analysis, the minimum safety factor for sliding and overturning can be 1.1 rather than 1.5 (§ 1807.2.3).
Guards: A required guard at a retaining wall is not required when the retaining wall is not accessible to the public (exception in § 1807.2.5).
Embedded posts used to support finishes: Posts embedded in earth shall not be used to provide lateral support to finishes (plaster, masonry, concrete) unless bracing is provided to meet deflection requirements (§ 1807.3.1).
Pole design relaxation: For isolated poles such as flagpoles or signs (and poles supporting buildings that can tolerate certain ground motion), the code permits using lateral bearing pressures equal to two times the tabular values under § 1806.3.4 — this is a permitted increase, not a default. Check application limits carefully.

Common mistakes

Designing retaining or foundation walls without using the lateral soil loads required by § 1610 or without an appropriate geotechnical investigation when required (§ 1807.1.1, § 1807.2.2).
Using the load combinations of Chapter 16 blindly for retaining wall stability checks instead of using the specific combination guidance in § 1807.2.3 (the code prescribes a different approach for safety‑factor checks).
Relying on embedded posts to restrain finishes (plaster, masonry) without adequate bracing as prohibited in § 1807.3.1.
Failing to treat timber poles to AWPA U1 when they are embedded in ground, or not following the specific backfill requirements for annular spaces around columns (§ 1807.3.1, § 1807.3.3).
Forgetting to provide guards where a walkway is close to a retaining wall with a sufficient vertical drop (36 in horizontal trigger, 30 in vertical drop trigger), or applying the guard exception mistakenly.

Worked example — deciding whether a guard is required and a quick sliding check

Scenario A — Guard trigger:

A 4‑ft (48 in) high retaining wall runs along a walkway whose edge is 30 in (0.83 ft) from the top of the retaining wall (horizontal distance = 30 in, which is less than 36 in). The grade below the walking surface at a point within 36 in of the open side is 40 in (vertical drop > 30 in). Is a guard required?
- § 1807.2.5.1 says a guard is required where the walking surface is located more than 30 in (762 mm) measured vertically to the surface or grade below at any point within 36 in (914 mm) horizontally to the edge of the open side. Here the vertical drop is 40 in and the walking surface is 30 in horizontally from the wall top (within 36 in). Therefore a guard is required; guard details must meet Sections 1607.9 / 1015.3 / 1015.4.

Scenario B — Quick check of sliding safety factor:

You calculate the net lateral force on a small retaining wall as 2,000 lb. The available soil resistance at the base (from bearing pressure and sliding resistance) is 3,400 lb. The safety factor against sliding is:
- SF = available soil resistance / net lateral force = 3,400 / 2,000 = 1.7
- Compare to minimum SF = 1.5 per § 1807.2.3 — the design passes the sliding safety factor requirement. If earthquake loads were included per the special rule, the minimum could be 1.1; however, the code prescribes how to account for earthquake loads in the combination (use 0.7× nominal earthquake loads) (§ 1807.2.3).

Scenario C — Embedment calculation (illustration, not a full design):

Equation 18‑1 in § 1807.3.2.1 is used for nonconstrained embedment depth d: d = 0.5 A {1 + [1 + (4.36 h/A)]^(1/2)}, where A = 2.34 P / (S1 b). To compute d you must obtain S1 (allowable lateral soil‑bearing pressure) from § 1806 tables or a geotechnical report. For illustration only, if you assume (for example only) S1 = 1,000 psf, P = 200 lb, b = 0.5 ft (6 in diameter), and h = 3 ft, you would compute A then d. NOTE: S1 must be taken from the soil tables or geotechnical investigation — the assumed S1 above is only for demonstration. The code limits the depth used in lateral pressure computations to 12 ft (§ 1807.3.2.1).

Related provisions

§ 1610 — Lateral soil loads (used for foundation and retaining wall design).
§ 1806 — Presumptive load‑bearing and lateral soil‑bearing values used in embedment and footing checks.
§ 1803 — Geotechnical investigations; when site‑specific soil parameters and recommendations are required.
§ 1808 — Foundation design provisions that support foundation walls.
§ 1607.9 — Guard requirements referenced for retaining‑wall guards. § 1015.3 / § 1015.4 — Guard height and opening limitations referenced for required guards.

Code references

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

CBC § 1807.2.5.1 High relevance — show source text
1807.2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607.9.

1807.2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807.2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807.3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807.3.1 through 1807.3.3 or ASABE EP 486.3.

1807.3.1 Limitations. The design procedures outlined in this section are subject to the following limitations:
1. The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
2. Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.
Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).

1807.3.2 Design criteria. The depth to resist lateral loads shall be determined using the design criteria established in Sections 1807.3.2.1 through 1807.3.2.3, or by other methods approved by the building official.

1807.3.2.1 Nonconstrained. The following formula shall be used in determining the depth of embedment required to resist lateral loads where lateral constraint is not provided at the ground surface, such as by a rigid floor or rigid ground surface pavement, and where lateral constraint is not provided above the ground surface, such as by a structural diaphragm. Equation 18-1 d = 0.5 A {1 + [1 + (4.36 h/A )] [1/2] }

where:

A = 2.34 P /( S 1 b ).

b = Diameter of round post or footing or diagonal dimension of square post or footing, feet (m).

d = Depth of embedment in earth in feet (m) but not over 12 feet (3658 mm) for purpose of computing lateral pressure.

h = Distance in feet (m) from ground surface to point of application of “ P .”

P = Applied lateral force in pounds (kN).

S 1 = Allowable lateral soil-bearing pressure as set forth in Section 1806.2 based on a depth of one-third the depth of embedment in pounds per square foot (psf) (kPa).

1807.3.2.2 Constrained. The following formula shall be used to determine the depth of embedment required to resist lateral loads where lateral constraint is provided at the ground surface, such as by a rigid floor or slab-on-ground.

Equation 18-2
CBC § 18-14 High relevance — show source text
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tions, lateral soil loads due to gravity load surcharge shall be considered gravity loads and seismic earth pressure increases due to earthquake shall be considered as seismic loads. For structures assigned to Seismic Design Category D, E or F, the design of retaining walls supporting more than 6 feet (1829 mm) of backfill height shall incorporate the additional seismic lateral earth pressure in accordance with the geotechnical investigation where required in Section 1803.2.

1807.2.3 Safety factor. Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.

Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

1807.2.4 Segmental retaining walls. Dry-cast concrete units used in the construction of segmental retaining walls shall comply with ASTM C1372.

1807.2.5 Guards. Guards shall be provided at retaining walls in accordance with Sections 1807.2.5.1 through 1807.2.5.3.

Exception: Guards are not required at retaining walls not accessible to the public.

1807.2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607.9.

1807.2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807.2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807.3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807.3.1 through 1807.3.3 or ASABE EP 486.3.

1807.3.1 Limitations. The design procedures outlined in this section are subject to the following limitations:
1. The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
2. Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.
Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).
CBC § 2.5 High relevance — show source text
1807 A .2.5 Guards. Guards shall be provided at retaining walls in accordance with Sections 1807 A .2.5.1 through 1807 A .2.5.3.

Exception: Guards are not required at retaining walls not accessible to the public.

1807 A .2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607 A .9.

1807 A .2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807 A .2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807 A .3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807 A .3.1 through 1807 A .3.3 or ASABE EP 486.3 Chapter 8 using soil properties and acceptance criteria determined by the geotechnical engineer in accordance with Section 1803A.

1807 A .3.1 Limitations. The design procedures outlined in this section are subject to the following limitations:
1. The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
2. Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.
Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).

1807 A .3.2 Design criteria. The depth to resist lateral loads shall be determined using the design criteria established in Sections 1807 A .3.2.1 through 1807 A .3.2.3, or by other methods approved by the building official.

1807 A .3.2.1 Nonconstrained. The following formula shall be used in determining the depth of embedment required to resist lateral loads where lateral constraint is not provided at the ground surface, such as by a rigid floor or rigid ground surface pavement, and where lateral constraint is not provided above the ground surface, such as by a structural diaphragm. Equation 18 A -1 d = 0.5 A {1 + [1 + (4.36 h/A )] [1/2] }

18A-10 2025 CALIFORNIA BUILDING CODE

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where:
CBC § 1806.3.4 High relevance — show source text
1806.3.4 Increase for poles. Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a [1] / 2 -inch (12.7 mm) motion at the ground surface due to short-term lateral loads shall be permitted to be designed using lateral bearing pressures equal to two times the tabular values.

SECTION 1807—FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED POSTS AND POLES

1807.1 Foundation walls. Foundation walls shall be designed and constructed in accordance with Sections 1807.1.1 through 1807.1.6. Foundation walls shall be supported by foundations designed in accordance with Section 1808.

1807.1.1 Design lateral soil loads. Foundation walls shall be designed for the lateral soil loads set forth in Section 1610.

1807.1.2 Unbalanced backfill height. 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, the unbalanced backfill height shall be permitted to be measured from the exterior finish ground level to the top of the interior concrete slab.

1807.1.3 Rubble stone foundation walls. [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Foundation walls of rough or random rubble stone shall be not less than 16 inches (406 mm) thick. Rubble stone shall not be used for foundation walls of structures assigned to Seismic Design Category C, D, E or F.

1807.1.4 Permanent wood foundation systems. [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Permanent wood foundation systems shall be designed and installed in accordance with AWC PWF. Lumber and plywood shall be preservative treated in accordance with AWPA U1 (Commodity Specification A, Special Requirement 4.2) and shall be identified in accordance with Section 2303.1.9.1.

1807.1.5 Concrete and masonry foundation walls. Concrete and masonry foundation walls shall be designed in accordance with Chapter 19 or 21, as applicable.

Exception: [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Concrete and masonry foundation walls shall be permitted to be designed and constructed in accordance with Section 1807.1.6.

1807.1.6 Prescriptive design of concrete and masonry foundation walls. [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Concrete and masonry foundation walls that are laterally supported at the top and bottom shall be permitted to be designed and constructed in accordance with this section.

1807.1.6.1 Foundation wall thickness. The thickness of prescriptively designed foundation walls shall be not less than the thickness of the wall supported, except that foundation walls of not less than 8-inch (203 mm) nominal width shall be permitted to support brick-veneered frame walls and 10-inch-wide (254 mm) cavity walls provided that the requirements of Section 1807.1.6.2 or 1807.1.6.3 are met.

**1807.1.6.2 Concrete foundation walls.
CBC § 2.3 High relevance — show source text
** Retaining walls shall be designed for the lateral soil loads determined by a geotechnical investigation in accordance with Section 1803A and shall not be less than eighty percent of the lateral soil loads determined in accor- dance with Section 1610A. For use with the load combinations, lateral soil loads due to gravity loads surcharge shall be considered gravity loads and seismic earth pressure increases due to earthquake shall be considered as seismic loads . For structures assigned to Seismic Design Category D, E or F, the design of retaining walls supporting more than 6 feet (1829 mm) of backfill height shall incorporate the additional seismic lateral earth pressure in accordance with the geotechnical investigation where required in Section 1803 A .2.

1807 A .2.3 Safety factor. Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 A shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.

Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

1807 A .2.4 Segmental retaining walls. Dry-cast concrete units used in the construction of segmental retaining walls shall comply with ASTM C1372.

1807 A .2.5 Guards. Guards shall be provided at retaining walls in accordance with Sections 1807 A .2.5.1 through 1807 A .2.5.3.

Exception: Guards are not required at retaining walls not accessible to the public.

1807 A .2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607 A .9.

1807 A .2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807 A .2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807 A .3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807 A .3.1 through 1807 A .3.3 or ASABE EP 486.3 Chapter 8 using soil properties and acceptance criteria determined by the geotechnical engineer in accordance with Section 1803A.
CBC § 1.1 High relevance — show source text
1807 A .1.1 Design lateral soil loads. Foundation walls shall be designed for the lateral soil loads determined by a geotechnical investigation, in accordance with Section 1803A.

1807 A .1.2 Unbalanced backfill height. 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, the unbalanced backfill height shall be permitted to be measured from the exterior finish ground level to the top of the interior concrete slab.

1807 A .1.3 Rubble stone foundation walls. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

1807 A .1.4 Permanent wood foundation systems. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

1807 A .1.5 Concrete and masonry foundation walls. Concrete and masonry foundation walls shall be designed in accordance with Chapter 19 A or 21 A, as applicable.

1807 A .2 Retaining walls. Retaining walls shall be designed in accordance with Sections 1807 A .2.1 through 1807 A .2.4.

1807 A .2.1 General. Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift .

1807 A .2.2 Design lateral soil loads. Retaining walls shall be designed for the lateral soil loads determined by a geotechnical investigation in accordance with Section 1803A and shall not be less than eighty percent of the lateral soil loads determined in accor- dance with Section 1610A. For use with the load combinations, lateral soil loads due to gravity loads surcharge shall be considered gravity loads and seismic earth pressure increases due to earthquake shall be considered as seismic loads . For structures assigned to Seismic Design Category D, E or F, the design of retaining walls supporting more than 6 feet (1829 mm) of backfill height shall incorporate the additional seismic lateral earth pressure in accordance with the geotechnical investigation where required in Section 1803 A .2.

1807 A .2.3 Safety factor. Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 A shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.

Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

1807 A .2.4 Segmental retaining walls. Dry-cast concrete units used in the construction of segmental retaining walls shall comply with ASTM C1372.
CBC § 3.1 High relevance — show source text
1806 A .3.1 Combined resistance. The total resistance to lateral loads shall be permitted to be determined by combining the values derived from the lateral bearing pressure and the lateral sliding resistance specified in Table 1806 A .2.

1806 A .3.2 Lateral sliding resistance limit. For clay, sandy clay, silty clay, clayey silt, silt and sandy silt, the lateral sliding resistance shall not exceed one-half the dead load.

1806 A .3.3 Increase for depth. The lateral bearing pressures specified in Table 1806 A .2 shall be permitted to be increased by the tabular value for each additional foot (305 mm) of depth to a value that is not greater than 15 times the tabular value.

1806 A .3.4 Increase for poles. Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a [1] / 2 -inch (12.7 mm) motion at the ground surface due to short-term lateral loads shall be permitted to be designed using lateral bearing pressures equal to two times the tabular values.

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SECTION 1807 A —FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED POSTS AND POLES

1807 A .1 Foundation walls. Foundation walls shall be designed and constructed in accordance with Sections 1807 A .1.1 through 1807 A .1.6. Foundation walls shall be supported by foundations designed in accordance with Section 1808 A .

1807 A .1.1 Design lateral soil loads. Foundation walls shall be designed for the lateral soil loads determined by a geotechnical investigation, in accordance with Section 1803A.

1807 A .1.2 Unbalanced backfill height. 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, the unbalanced backfill height shall be permitted to be measured from the exterior finish ground level to the top of the interior concrete slab.

1807 A .1.3 Rubble stone foundation walls. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

1807 A .1.4 Permanent wood foundation systems. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

1807 A .1.5 Concrete and masonry foundation walls. Concrete and masonry foundation walls shall be designed in accordance with Chapter 19 A or 21 A, as applicable.

1807 A .2 Retaining walls. Retaining walls shall be designed in accordance with Sections 1807 A .2.1 through 1807 A .2.4.
CBC § 1806.3.2. High relevance — show source text
Coefficient to be multiplied by the dead load.
b. Cohesion value to be multiplied by the contact area, as limited by Section 1806.3.2.|For SI: 1 pound per square foot = 0.0479 kPa, 1 pound per square foot per foot = 0.157 kPa/m.
a. Coefficient to be multiplied by the dead load.
b. Cohesion value to be multiplied by the contact area, as limited by Section 1806.3.2.|

1806.3 Lateral load resistance. Where the presumptive values of Table 1806.2 are used to determine resistance to lateral loads, the calculations shall be in accordance with Sections 1806.3.1 through 1806.3.4.

1806.3.1 Combined resistance. The total resistance to lateral loads shall be permitted to be determined by combining the values derived from the lateral bearing pressure and the lateral sliding resistance specified in Table 1806.2.

1806.3.2 Lateral sliding resistance limit. For clay, sandy clay, silty clay, clayey silt, silt and sandy silt, the lateral sliding resistance shall not exceed one-half the dead load.

1806.3.3 Increase for depth. The lateral bearing pressures specified in Table 1806.2 shall be permitted to be increased by the tabular value for each additional foot (305 mm) of depth to a value that is not greater than 15 times the tabular value.

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SOILS AND FOUNDATIONS

1806.3.4 Increase for poles. Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a [1] / 2 -inch (12.7 mm) motion at the ground surface due to short-term lateral loads shall be permitted to be designed using lateral bearing pressures equal to two times the tabular values.

SECTION 1807—FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED POSTS AND POLES

1807.1 Foundation walls. Foundation walls shall be designed and constructed in accordance with Sections 1807.1.1 through 1807.1.6. Foundation walls shall be supported by foundations designed in accordance with Section 1808.

1807.1.1 Design lateral soil loads. Foundation walls shall be designed for the lateral soil loads set forth in Section 1610.

1807.1.2 Unbalanced backfill height. 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, the unbalanced backfill height shall be permitted to be measured from the exterior finish ground level to the top of the interior concrete slab.

1807.1.3 Rubble stone foundation walls. [OSHPD 1R, 2 & 5] Not permitted by OSHPD. Foundation walls of rough or random rubble stone shall be not less than 16 inches (406 mm) thick. Rubble stone shall not be used for foundation walls of structures assigned to Seismic Design Category C, D, E or F.
CBC § 18-35 High relevance — show source text
[OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-35

CHAPTER 18A SOILS AND FOUNDATIONS. . . . . . . . . . . . . .18A-1

1801A General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

1802A Design Basis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

1803A Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . . . 18A-3

1804A Excavation, Grading and Fill . . . . . . . . . . . . . . . . . . . . . 18A-7

1805A Dampproofing and Waterproofing . . . . . . . . . . . . . . . 18A-7

1806A Presumptive Load-Bearing Values of Soils. . . . . . . . 18A-9

CONTENTS

1807A Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . . . 18A-10

1808A Foundations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-11

1809A Shallow Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-14

1810A Deep Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-15

1811A Prestressed Rock and Soil Foundation

Anchors [OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . 18A-25

1812A Earth Retaining Shoring . . . . . . . . . . . . . . . . . . . . . . . . 18A-26

1813A Vibro Stone Columns for Ground

Improvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-29

CHAPTER 19 CONCRETE. . . . . . . . . . . . . . . . . . . . . . . . . . . 19-1

1901 General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19-3
CBC § 1807.1.6.3.2 Medium relevance — show source text
1807.1.6.3.2 Seismic requirements. Based on the seismic design category assigned to the structure in accordance with Section 1613, masonry foundation walls designed using Tables 1807.2.5.
1. Seismic Design Categories A and B. No additional seismic requirements.
2. Seismic Design Category C. A design using Tables 1807.1.6.3(1) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.3 of TMS 402.
3. Seismic Design Category D. A design using Tables 1807.1.6.3(2) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.4 of TMS 402.
4. Seismic Design Categories E and F. A design using Tables 1807.1.6.3(2) through 1807.1.6.3(4) is subject to the seismic requirements of Section 7.4.5 of TMS 402.
1807.2 Retaining walls. Retaining walls shall be designed in accordance with Sections 1807.2.1 through 1807.2.4.

1807.2.1 General. Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift.

1807.2.2 Design lateral soil loads. Retaining walls shall be designed for the lateral soil loads set forth in Section 1610. [OSHPD 1R, 2 & 5] Retaining wall lateral soil loads determined by a geotechnical investigation report in accordance with Section 1803.5.12 and shall not be less than 80 percent of the lateral soil loads determined in accordance with Section 1610. For use with the load combina-

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tions, lateral soil loads due to gravity load surcharge shall be considered gravity loads and seismic earth pressure increases due to earthquake shall be considered as seismic loads. For structures assigned to Seismic Design Category D, E or F, the design of retaining walls supporting more than 6 feet (1829 mm) of backfill height shall incorporate the additional seismic lateral earth pressure in accordance with the geotechnical investigation where required in Section 1803.2.

1807.2.3 Safety factor. Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.

Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

1807.2.4 Segmental retaining walls. Dry-cast concrete units used in the construction of segmental retaining walls shall comply with ASTM C1372.
CBC § 18-3 Medium relevance — show source text
1803 Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . 18-3

1804 Excavation, Grading and Fill. . . . . . . . . . . . . . . . . . . . 18-7

1805 Dampproofing and Waterproofing . . . . . . . . . . . . . . 18-7

1806 Presumptive Load-Bearing Values of Soils . . . . . . . 18-9

1807 Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . 18-10

1808 Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16

1809 Shallow Foundations . . . . . . . . . . . . . . . . . . . . . . . . . 18-18

1810 Deep Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20

1811 Prestressed Rock and Soil Foundation

Anchors [OSHPD 1R, 2 & 5]. . . . . . . . . . . . . . . . . . . . . 18-31

1812 Earth Retaining Shoring

[OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-32

1813 Vibro Stone Columns for Ground Improvement

[OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-35

CHAPTER 18A SOILS AND FOUNDATIONS. . . . . . . . . . . . . .18A-1

1801A General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

1802A Design Basis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

1803A Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . . . 18A-3

1804A Excavation, Grading and Fill . . . . . . . . . . . . . . . . . . . . . 18A-7

1805A Dampproofing and Waterproofing . . . . . . . . . . . . . . . 18A-7

1806A Presumptive Load-Bearing Values of Soils. . . . . . . . 18A-9

CONTENTS

1807A Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . . . 18A-10
CBC § 2.4 Medium relevance — show source text
on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

FOUNDATIONS

R404.2.4 Backfilling. Wood foundation walls shall not be backfilled until the basement floor and first floor have been constructed or the walls have been braced. For crawl space construction, backfill or bracing shall be installed on the interior of the walls prior to placing backfill on the exterior.

R404.2.5 Drainage and dampproofing. Wood foundation basements shall be drained and dampproofed in accordance with Sections R405 and R406, respectively.

R404.2.6 Fastening. Wood structural panel foundation wall sheathing shall be attached to framing in accordance with Table R602.3(1) and Section R402.1.1.

R404.3 Wood sill plates. Wood sill plates shall be not less than 2-inch by 4-inch (51 mm by 102 mm) nominal lumber. Sill plate anchorage shall be in accordance with Sections R403.1.6 and R602.11.

R404.4 Retaining walls. Retaining walls that are not laterally supported at the top and that retain in excess of 48 inches (1219 mm) of unbalanced fill, or retaining walls exceeding 24 inches (610 mm) in height that resist lateral loads in addition to soil, shall be designed in accordance with accepted engineering practice to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning. This section shall not apply to foundation walls supporting buildings.

R404.5 Precast concrete foundation walls.

R404.5.1 Design. Precast concrete foundation walls shall be designed in accordance with accepted engineering practice. The design and manufacture of precast concrete foundation wall panels shall comply with the materials requirements of Section R402.3 or ACI 318. The panel design drawings shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed in accordance with Section R106.1.

R404.5.2 Precast concrete foundation design drawings. Precast concrete foundation wall design drawings shall be submitted to the building official and approved prior to installation. Drawings shall include, at a minimum, the following information:
1. Design loading as applicable.
2. Footing design and material.
3. Concentrated loads and their points of application.
4. Soil bearing capacity.
5. Maximum allowable total uniform load.
6. Seismic design category.
7. Basic wind speed.
R404.5.3 Identification. Precast concrete foundation wall panels shall be identified by a certificate of inspection label issued by an approved third-party inspection agency.

SECTION R405 —FOUNDATION DRAINAGE

R405.1 Concrete or masonry foundations. Drains shall be provided around concrete or masonry foundations that retain earth and enclose habitable or usable spaces located below grade. Drainage tiles, gravel or crushed stone drains, perforated pipe or other approved systems or materials shall be installed at or below the top of the footing or below the bottom of the slab and shall discharge by gravity or mechanical means into an approved drainage system. Gravel or crushed stone drains shall extend not less than 1 foot (305 mm) beyond the outside edge of the footing and 6 inches (152 mm) above the top of the footing and be covered with an approved filter membrane material. The top of open joints of drain tiles shall be protected with strips of building paper.

Frequently asked questions

When do I need a geotechnical report for a retaining wall or foundation wall?

If the design depends on site soil properties (typical for walls retaining significant fills, walls > certain heights, or those in seismic regions), the CBC requires design lateral soil loads determined by a geotechnical investigation in accordance with § 1803 and § 1807.2.2 (or Chapter 18A variants).

Can I use a simple prescriptive table instead of engineering calculations?

Prescriptive provisions exist for some foundation walls (§ 1807.1.6) and for certain residential walls in the Residential Code, but where unbalanced backfill or height exceeds prescriptive limits, or for retaining walls resisting more than specified fills, engineered design per § 1610 or a geotechnical report is required.

Are embedded posts allowed to support plaster or masonry directly?

No — posts embedded in earth shall not be used to provide lateral support for finishes like plaster, masonry or concrete unless bracing is provided that develops the limited deflection required (§ 1807.3.1).

How strong must concrete backfill be around an embedded post?

If using concrete as the annular backfill around a column not in a poured footing, the concrete must have a specified compressive strength of not less than 2,000 psi (§ 1807.3.3).

What safety factor does the code require for retaining walls?

The code requires a minimum safety factor of 1.5 against sliding and overturning; if earthquake loads are included, the minimum can be 1.1 when following the prescribed load combination procedure in § 1807.2.3.

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Shallow & Deep Foundations, Retaining Walls & Ground Improvement

California Building Code