Skip to content
CrossBeamStart a pre-check

Building Code Reference

Got a CRC R602.11 correction?

Anchor bolt plate washers seismic

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 R602.11 requires 3-inch by 3-inch by 0.229-inch (7 gauge) steel plate washers at every anchor bolt connecting the sill plate to the foundation in Seismic Design Categories D0, D1, and D2. Standard round washers don't cut it in these zones. The plate washer distributes the bolt's holding force across more wood fiber, which keeps the sill plate from pulling free during lateral shaking. Most single-family residential and ADU permits in Orange County fall under SDC D or higher, making this section nearly universal on new construction and addition framing.

How to fix it

  1. Confirm your project is in SDC D0, D1, or D2

    R602.11.1 plate washers are required in Seismic Design Categories D0, D1, and D2, and for townhouses in SDC C. Virtually all of coastal and inland Orange County falls in these categories, but check the geotechnical or soils report, or look at the seismic site classification on your structural cover sheet. If your SDC is C or lower (and the building is not a townhouse in SDC C), standard round washers are fine and you can stop here. If it's D0, D1, or D2, proceed with the steps below.

  2. Add a plate washer detail to your foundation plan

    On the foundation or framing plan, add a note or detail callout that reads: "Provide 3" x 3" x 0.229" (7 gauge) steel plate washers between nut and sill plate at all anchor bolt locations per CRC R602.11." If your plan already has a sill plate detail (often shown as a section cut at the foundation), add the plate washer to that detail with a leader note. A blown-up section at 1"=1'-0" or larger works well. Show the plate washer sandwiched between the sill plate and the nut.

  3. Cross-reference anchor bolt spacing on the same sheet

    Plan-checkers reviewing R602.11 typically cross-check anchor bolt spacing (CRC R403.1.6) at the same time. While you're revising the sheet, confirm your plans show anchor bolts at 6 feet on center maximum, with bolts within 12 inches of each end of each sill plate section. A single detail that calls out both the bolt spacing and the plate washer spec resolves both corrections in one resubmittal.

  4. Specify the plate washer material

    The code calls for steel plate washers. For standard interior sill plates, plain steel plate washers are acceptable. If the sill plate is preservative-treated lumber, use hot-dip galvanized or stainless steel plate washers to avoid corrosion from the chemicals in treated wood. CRC R304.1 lists where naturally durable or preservative-treated wood is required, such as sills and sleepers on a concrete slab in direct contact with the ground, unless an impervious moisture barrier separates them. Call out the material on your detail to preempt a follow-up correction.

  5. Update the hardware schedule or nailing schedule

    Many sets include a hardware schedule or connector schedule on the structural or framing sheets. Add a line for the R602.11 plate washer: size 3" x 3" x 0.229" (7 gauge), one per anchor bolt, SDC D0-D2. Some plan-checkers want to see this in the schedule even when it's shown in a section detail. Including it in both places costs nothing and prevents a second round.

  6. Address existing anchor bolts on remodel or ADU projects

    If you're adding to an existing structure and the existing sill plates are already bolted down, check what hardware was used. If the existing bolts have standard round washers, you have two paths: (1) document that the existing anchorage was installed and inspected under a prior permit and the scope of work doesn't disturb that portion of the sill plate, or (2) add retrofit plate washers by removing the nut, sliding a plate washer over the bolt, and re-torquing. Path 1 usually works for additions that don't touch the existing framing. Path 2 is required if the remodel disturbs the sill plate.

  7. Resubmit with a written response to each correction item

    On resubmittal, include a response letter that lists each correction by number and explains exactly where the plan was revised. For the R602.11 correction, write: "Sheet [X], Detail [Y]: Added 3" x 3" x 0.229" steel plate washer callout at all anchor bolt locations per CRC R602.11. See revised foundation plan note and sill plate section detail." Plan-checkers approve faster when they can match each correction to a specific sheet and detail number without hunting.

Take the CRC R602.11 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 R602.11 most often when the structural or framing details show standard hardware-store washers at the anchor bolt locations instead of the specified plate washers. The correction note usually reads something like "provide 3x3x0.229 (7 gauge) plate washers per CRC R602.11" on the foundation plan or framing detail sheet.

A second common trigger is the bolts being called out correctly but the washer spec missing entirely. A contractor might note "anchor bolts per CRC R403.1.6" and get the bolt diameter, spacing, and embedment right, while the plate washer requirement gets overlooked because it lives in Chapter 6 (wall framing) rather than Chapter 4 (foundations). Plan-checkers are trained to look for it in both places, so the omission gets caught.

Projects that convert a garage to an ADU or add a room over an existing slab often get flagged because the existing anchor bolts were installed before R602.11 plate washers were required or enforced locally. If the remodel touches the sill plate, a plan-checker may require documenting the existing hardware or adding retrofit plate washers.

Finally, framing plans that use generic notes like "hardware per engineer" without a specific plate washer callout get flagged when no engineering letter accompanies the set. Without either an explicit R602.11 reference or a signed engineer's stamp specifying equivalent hardware, the plan-checker defaults to rejecting the sheet.

The official code

CRC R602.11 — Anchor Bolt Plate Washers, 2025 California Residential Code

Read the source →

Common questions

Do I need plate washers on an ADU if the foundation was already poured?
Yes, if the ADU is new construction on a new slab or foundation in SDC D0-D2, R602.11 applies to every anchor bolt. If you're converting an existing garage or room and the slab and anchor bolts were installed under a prior permit, you may be able to document the existing anchorage rather than retrofit. The key is whether your current scope of work disturbs the sill plate. If you're removing and re-setting the sill, the new connection must meet current code including the plate washers. If the sill stays in place and is not part of your scope, document that on your plans with a note like: "Existing anchor bolt hardware per original permit [number]; sill plate not disturbed by this scope."
What's the difference between a regular washer and a plate washer?
A standard round washer is typically 1.5 to 2 inches in diameter. A plate washer per R602.11 is 3 inches square and 0.229 inch (7 gauge) thick, giving it roughly four times the bearing area. That extra area matters in a seismic event: when the wall tries to rack sideways, the anchor bolt tries to pull up through the sill plate. A small round washer can cut through the wood fiber under that load. A 3x3 plate washer distributes the force over more wood and stays in place. The difference in cost is a few dollars per bolt. The difference in performance in a real earthquake is significant.
Can I use a Simpson or USP plate washer instead of cutting my own?
Yes. Pre-cut steel plate washers sized 3x3x0.229 (7 gauge) are available from Simpson Strong-Tie and other hardware suppliers. As long as the product meets the minimum dimensions in R602.11, you don't need to specify a brand on your plans. Just call out the minimum size and material. If you're on a pressure-treated sill plate, specify galvanized or stainless to match the treated lumber requirement.
Does R602.11 apply to the garage sill plate too?
Yes. R602.11 applies to all sill plates in the structure, not just the main living areas. If your plans include a garage, the garage sill plates need the same plate washer spec at each anchor bolt location. A common mistake is detailing the main house correctly and leaving the garage framing plan without the callout. Plan-checkers catch this because they review all sheets.
What SDC is Anaheim or most of Orange County?
Most of Orange County, including Anaheim, falls in Seismic Design Category D1 or D2, which means R602.11 plate washers are required on virtually every new residential project in the area. The exact SDC for a specific parcel depends on the mapped spectral acceleration values and site soil class from a geotechnical report. Your structural engineer of record will confirm this on the structural cover sheet. If no structural engineer is required for your project (small additions, simple ADUs), check the seismic design maps at the USGS Unified Hazard Tool using your site's coordinates.
Will the inspector check for plate washers in the field?
Yes. During the framing inspection, the inspector will check that the plate washers are installed at every anchor bolt before the framing is covered with sheathing. If they're missing, you'll get a correction on the inspection card and the inspector won't sign off on framing. Buying and installing the right washers before the framing inspection is far faster than trying to add them after framing is up. At that point the sill plate is buried under studs and plates and access is tight.

Related corrections

Check my plans for this →