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Building Code Reference

Got a CRC R403.1.6 correction?

Anchor bolt spacing

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 R403.1.6 requires sill plates on concrete or masonry foundations to be bolted down with 1/2-inch diameter anchor bolts spaced no more than 6 feet apart. Each bolt must embed at least 7 inches into the concrete, and there must be a bolt within 12 inches of each plate end. In Seismic Design Categories D0, D1, and D2 — which covers most of Southern California including Orange County — 3" x 3" x 0.229" (7 gauge) steel plate washers are required at every bolt. The section applies to any new single-family or ADU project with a poured or masonry foundation, and corrections for it show up frequently in Orange County plan checks.

How to fix it

  1. Add anchor bolt layout to foundation plan

    On your foundation plan sheet, mark every anchor bolt location with a symbol (typically a circle with a center dot). Dimension the spacing between bolts — the maximum is 6 feet on center. If you have multiple sill plate runs, each run needs its own bolt layout shown. A general note saying ‘anchor bolts per code’ is not enough; the plan-checker needs to verify spacing from the drawing.

  2. Call out end bolts within 12 inches of each plate end

    At each end of every sill plate segment, there must be a bolt not more than 12 inches, and not less than seven bolt diameters, from the plate end. This applies to both ends of a continuous run and to each side of any opening or gap. Check corners, garage door openings, and any location where the sill plate starts or stops. Add a dimension on the plan from the last bolt to the plate end, labeled clearly. Common mistake: spacing bolts evenly across a run and ending up with 18 inches at the tail.

  3. Show 7-inch embedment on the foundation section detail

    Your foundation section detail (typically on the structural or architectural sheets) must show the anchor bolt with a dimension of 7 inches minimum into the concrete. A J-bolt or L-bolt silhouette drawn without a dimension tag will get flagged. If your detail sheet uses a standard foundation callout block, verify the embed depth is included in that callout, not just implied.

  4. Specify 3" x 3" x 0.229" plate washers for seismic zones

    Orange County falls in Seismic Design Category D1 or D2 depending on the jurisdiction and site. In those categories, anchor bolts along required braced wall lines need a 3-inch by 3-inch by 0.229-inch (7 gauge) steel plate washer unless approved anchor straps are used; cut washers are allowed only in wall lines with no braced wall panels. Add this to your hardware schedule and to your foundation detail. If your detail currently shows a standard round washer, change it to the square plate washer spec. The size and thickness both matter — 3x3 at 0.229 inch (7 gauge) minimum, not a thinner plate.

  5. Label bolt diameter and material in the hardware schedule

    The section requires 1/2-inch diameter minimum bolts. Call this out in your hardware schedule or in a foundation note: ‘1/2" dia. x min. 10" long (7" embed), ASTM F1554 Grade 36 or equivalent.’ Many standard details already include this; if yours doesn’t, add a hardware note or a foundation general note. The plan-checker shouldn’t have to guess the bolt spec.

  6. Check sill plate runs at garage and step-down conditions

    Step-down foundations, split-level slab edges, and garage perimeter walls are frequent trouble spots. The sill plate on each level or segment is treated independently for the end-bolt rule. If the garage sill plate is a short run of 3 feet, it still needs two bolts, one within 12 inches of each end. Map these conditions individually on your plan — don’t assume they’re covered by the main-house bolt layout.

  7. Verify bolt count on short plate segments

    Every plate section needs at least two bolts, one within 12 inches of each end, however short it is. The exception is a wall 24 inches or shorter connecting offset braced wall panels: it needs one bolt in the center third of the plate, and one 12 inches or shorter needs none, if it is tied to the adjacent braced wall panels per Item 9 of Table R602.3(1). Put a note or detail callout for any short run so it’s unambiguous on resubmittal.

Take the CRC R403.1.6 fix steps with you

All 7 steps in one email, so you have them on site instead of on this page.

Why you got flagged

Plan-checkers flag CRC R403.1.6 in a few consistent patterns.

The most common issue is a missing bolt layout on the foundation plan. Many contractors show the sill plate on the plans without marking anchor bolt locations, spacing dimensions, or end-bolt callouts. The city needs to verify maximum 6-foot spacing and the 12-inch end-bolt rule from the drawings alone. If it’s not on the sheet, it gets a correction every time.

The second pattern is incorrect end-bolt placement. The 12-inch rule means the first and last bolt on every plate segment must fall within 12 inches of the plate end. Sill plates around corners, garage openings, or step-down foundations often get their end bolts pushed past 12 inches when the drafter fits bolts at even spacing across the whole run without checking the ends independently.

The third common flag is the missing plate washer detail. In California’s higher seismic zones, and Orange County falls into SDC D1 or D2 in most jurisdictions, the 3" x 3" x 0.229" (7 gauge) steel plate washer is mandatory at anchor bolts along braced wall lines. Many sets show standard round washers in the hardware schedule or omit washers from the foundation detail entirely. The plate washer requirement often gets called out as a separate correction even when the bolt spacing itself is fine.

A fourth scenario involves slab-on-grade construction where the embed depth isn’t shown explicitly. The 7-inch minimum embedment into concrete can’t be assumed — it has to be called out on the section detail or in a general note. If your foundation detail shows a J-bolt silhouette without a dimension, expect a correction.

The official code

2025 California Residential Code, Chapter 4 Foundations — California Building Standards Commission

Read the source →

Common questions

Does CRC R403.1.6 require plate washers on every project?
Only in Seismic Design Categories D0, D1, and D2. Most of Orange County and Southern California falls into D1 or D2, so if you’re building in Anaheim, Santa Ana, Irvine, or anywhere in OC, plan on including the 3" x 3" x 0.229" (7 gauge) steel plate washers. Projects in lower seismic zones (SDC A, B, or C) don’t have the plate washer requirement under this section. Your geotechnical report or site soils data will confirm the SDC for your specific address.
What is the minimum anchor bolt embed depth in CRC R403.1.6?
7 inches into the concrete or masonry. This means the bolt shank runs 7 inches below the top of the foundation. With a standard J-bolt or L-bolt, the total bolt length needs to account for the plate, sill, washer, and nut above the slab plus the 7-inch embed below. A common spec is a 10-inch bolt for a 2x6 sill on a flat slab, which gives 7 inches of embed after accounting for the plate thickness, washer, and nut. Always show the embed dimension on your section detail.
How close to the plate end does the last anchor bolt need to be?
Within 12 inches of the plate end. Both ends of every sill plate segment count independently. If a sill plate terminates at a corner, at a door opening, or at any interruption in the plate, the last bolt before that termination must be within 12 inches of it. This is one of the most commonly missed R403.1.6 requirements because drafters often lay out bolts at even spacing without explicitly checking the tail distance at each end.
Can I use epoxy-set anchors to satisfy R403.1.6?
Yes, post-installed anchors with an ICC Evaluation Report (ICC-ES ESR) covering their use in this application are an accepted alternative, but the same spacing, end-bolt, embed depth, and plate washer requirements still apply. You’ll need to note the product name, ESR number, and installation spec on the plans. The inspector will check that the anchor is installed per the ESR, so the install depth and edge distance requirements from the ESR are just as binding as the code’s own minimums.
Does R403.1.6 apply to ADU projects on existing foundations?
For new construction or a new addition with a new foundation, yes. If you’re attaching to an existing foundation that was originally permitted and built, the city may accept the existing anchor bolt condition for those walls. But any new sill plate on new concrete, including a garage conversion ADU with a new stem wall or a new room addition, has to meet R403.1.6. When in doubt, call your plan-checker before design. Some cities require you to retrofit anchor bolts on the existing foundation too, especially in higher seismic zones.
What size plate washer does CRC R403.1.6 require?
3 inches by 3 inches by 0.229 inch (7 gauge) thick, square, steel. This is a larger, heavier washer than the standard round cut washer. The square shape distributes the load across a wider area of the sill plate, which is why standard hardware-store washers don’t satisfy this section. You can find code-compliant plate washers at most lumberyards and structural hardware suppliers. Specify ‘3" x 3" x 0.229" (7 ga.) steel plate washer’ in your hardware schedule to avoid ambiguity on the job site.

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