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Building Code Reference

Got a CRC R404.1 correction?

Foundation wall design

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CRC R404.1 is the California Residential Code section that governs the design and construction of concrete and masonry foundation walls. It sets minimum wall thickness, required steel reinforcement, and prescriptive table requirements based on wall height and unbalanced backfill depth. Any foundation wall that retains soil on one side and bears the load of the structure above must comply with R404.1 or be designed by a licensed engineer. Most single-family residential and ADU permits get flagged here when the plans do not detail the wall dimensions, rebar spacing, or specify the concrete mix strength required by the prescriptive tables.

How to fix it

  1. Pull the R404.1 prescriptive table that matches your wall

    Start by identifying your wall height and unbalanced backfill depth. CRC R404.1 includes prescriptive tables (Tables R404.1.3.2(1) through R404.1.3.2(8) for concrete walls, Tables R404.1.2.1(1) through R404.1.2.1(4) for masonry) that list minimum wall thickness and required vertical rebar size and spacing for each combination. If your wall is 8 feet tall with 7 feet of unbalanced backfill, read directly from the 8-foot-wall row. Write the table number on your plans — the plan-checker needs to see which table row you used.

  2. Add a foundation wall section detail to the structural sheets

    Create a wall section detail at 1/4 inch = 1 foot minimum scale showing wall thickness, footing width and depth, vertical rebar size (e.g., #5 at 32 inches on center), horizontal rebar, and concrete cover. Label the concrete compressive strength (f'c = 2,500 psi minimum for most residential concrete walls; 3,000 psi is common in practice). This detail should appear on the structural or foundation plan sheet, not buried in a general notes table.

  3. Dimension the unbalanced backfill height on the site section

    Show the finished grade elevation on both the inside and outside of the wall on a building section or site-grading plan. The unbalanced backfill height is the difference between finished exterior grade and the interior floor or lowest interior grade. Plan-checkers pull this number directly from your drawings to confirm you are in the right table row. If you leave it off, they will ask for it — that is a correction you do not need.

  4. Call out concrete strength and mix requirements

    CRC Table R402.2 sets minimum concrete compressive strength. Note f'c on your foundation plan or in the general structural notes. For most standard residential concrete walls, 2,500 psi at 28 days is the floor; many engineers and local jurisdictions ask for 3,000 psi, especially in seismic zones or where the wall is also waterproofed. If you are in an area with sulfate soils, the mix requirements change — your soils report will call this out. State the strength; do not leave it implied.

  5. Tie the rebar schedule to the prescriptive table or engineering

    If you are using the prescriptive path, note the specific table and row number next to your rebar call-out on the detail: for example, "#5 vertical bars at 39 in. o.c. per CRC Table R404.1.3.2(2), 6-in. flat wall, 8 ft wall, 6 ft unbalanced fill, GW/GP/SW/SP soil." If you are using engineered design, the engineer of record must stamp the foundation wall section and reference R404.1 explicitly. An engineering calculation package submitted without a stamped drawing tied to R404.1 will still generate a correction.

  6. Verify footing compliance with CRC R403.1

    R404.1 is almost always cited alongside R403.1 because the footing supports the foundation wall. Before resubmitting, check that your footing detail shows the required depth below undisturbed soil, minimum width and thickness, and footing rebar per R403.1.3. Getting R404.1 right while leaving R403.1 details vague will cost you another correction round.

  7. Check drainage behind the wall per CRC R405.1

    R404.1 covers the structural wall; R405.1 requires foundation drainage — gravel backfill or a drain tile system that carries groundwater away from the wall before it builds up hydrostatic pressure. Plan-checkers often flag both sections together on basement and split-level foundations. Add a drainage call-out on your foundation plan: drain tile, perforated pipe or a gravel drain at or below the top of the footing, gravel extending 1 foot beyond the footing and 6 inches above it under filter fabric, discharging to an approved system.

  8. If the prescriptive tables do not cover your condition, get engineering

    The prescriptive tables in R404.1 cover standard residential conditions: wall heights up to 10 feet, typical fill heights, and standard soil assumptions. If your project has taller walls, unusual soil conditions (expansive clay, high groundwater, fill over 4 feet), or a lot slope that creates asymmetric loading, the prescriptive path does not apply. You need a licensed structural engineer to design the wall and submit stamped calculations. The plan-checker will reject a prescriptive table reference if your actual condition falls outside the table's scope.

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Why you got flagged

Here is why plan-checkers flag R404.1: the most common correction is missing foundation wall details on the structural sheets. A plan-checker reviewing a new single-family home or ADU will look for a foundation plan and sections that call out wall thickness, concrete compressive strength, and vertical rebar size and spacing. When those details are absent or only say something vague like "foundation per code," R404.1 gets flagged every time.

The second scenario involves plans that show a pony wall or stem wall but fail to account for the unbalanced backfill height. Backfill exerts lateral soil pressure on the wall, and Tables R404.1.3.2(2) through R404.1.3.2(8) set rebar requirements that change with both wall height and the depth of backfill retained. A wall drawn at 8 feet tall retaining 6 feet of soil needs heavier reinforcement than the same wall retaining 2 feet — the plans have to show which condition applies and prove the rebar chosen matches the table.

The third common trigger is an engineered design that came in without the required engineer-of-record stamp or without the prescriptive tables being correctly referenced. When an applicant submits engineering calculations for an atypical condition — deep fill, expansive soils, tall stem walls — plan-checkers still need to see an explicit reference to R404.1 and the engineer's license number on the stamped sheet. A generic soils report or a detached structural calculation package without the wall section tied to R404.1 will generate a correction.

A less obvious scenario: retaining walls that also serve as foundation walls on a sloped lot. If the plans show a daylight basement or a split-level foundation, the below-grade portion of the perimeter wall is acting as a retaining wall and a foundation wall simultaneously. Plan-checkers will flag R404.1 along with the drainage requirement under R405.1 to make sure both the structural and waterproofing sides of the wall are addressed.

The official code

California Residential Code Part 2.5 — 2025 Edition (Title 24), California Building Standards Commission

Read the source →

Common questions

What is the minimum concrete wall thickness for CRC R404.1?
The minimum thickness depends on wall height and unbalanced backfill depth, per the prescriptive tables in R404.1. For a plain concrete wall (no rebar), the minimum is typically 7.5 inches, but most residential projects use reinforced concrete at 6 inches with appropriate rebar. Once you start retaining more than 4 feet of fill or the wall exceeds 8 feet in height, the tables require heavier rebar or a thicker wall. The safest move is to read directly from the Table R404.1.3.2 table for your wall type using your actual wall height and backfill depth rather than guessing.
Does CRC R404.1 apply to ADU foundation walls?
Yes. CRC R404.1 applies to any new concrete or masonry foundation wall built as part of a residential project, including ADUs, whether attached or detached. An ADU on a flat lot with shallow backfill may fall in the lightest prescriptive table row (small rebar, standard spacing), but the plans still need to show the table reference and the wall detail. ADU corrections letters frequently flag R404.1 when the foundation plan just shows a footing without a wall section — plan-checkers need both.
Can I use the prescriptive tables instead of hiring a structural engineer?
Yes, if your conditions fall within the table's scope. The prescriptive tables in CRC R404.1 cover reinforced concrete walls up to 10 feet tall and standard residential fill depths. If your wall is within those bounds and your soils report does not flag unusual conditions (expansive clay, high water table, fill over 4 feet), the prescriptive path is legal and widely used. You still need a complete wall section detail referencing the specific table row. If any condition falls outside the table — unusual soils, taller walls, asymmetric loading from a sloped lot — a licensed structural engineer needs to design the wall.
What rebar does R404.1 require for an 8-foot concrete foundation wall?
It depends on the unbalanced backfill height. For an 8-foot, 6-inch flat concrete wall, Table R404.1.3.2(2) lists rebar requirements for each backfill depth. At 4 feet of backfill, the table requires no vertical bars (NR); at 6 feet of backfill, it requires #5 bars at 39 inches or #6 bars at 35 to 48 inches, depending on soil class. Always read the current adopted 2025 edition of the CRC directly — the specific bar size and spacing are in the table, and they are the numbers the plan-checker will check your drawings against.
My stem wall is only 2 feet tall — do I still need to show R404.1 details?
Yes, if it is retaining any soil. A short stem wall still has unbalanced backfill pressure on it, and R404.1 still applies. The table rows for low walls with shallow backfill are less demanding, but the plan-checker will still want to see the wall thickness, rebar (or confirmation that a plain concrete wall meets the table requirement), and concrete strength called out on the drawings. "Short wall" is not an exception. The detail takes 15 minutes to add; skipping it costs you a correction round.
What is the difference between CRC R404.1 and CBC 1806 for foundation walls?
CRC R404.1 is the residential code provision and applies to single-family homes, duplexes, and ADUs. CBC 1806 covers foundation wall design under the commercial building code. If your project is a single-family residence or a residential ADU, R404.1 is your code. If you are building a mixed-use building, multi-unit residential over three stories, or any project that falls under the CBC instead of the CRC, Section 1806 applies. The plan-checker's corrections letter will cite the correct code for your project type — if you see R404.1 cited, you are under the CRC.

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