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Home / Code Guides / Anchor Bolts

Sill Plate Anchor Bolt Code — Size, Spacing & Placement

Anchor bolts are the entire connection between the house and the planet, and the IRC specs them like it: a diameter, an embedment, a spacing, and rules for where the first and last bolt must land.

RequirementModel Code StandardSection
Size & embedment1/2 in. minimum diameter bolts embedded at least 7 in. into concrete or grouted masonryIRC R403.1.6
SpacingMaximum 6 ft on center; sill plates supporting braced wall panels in higher seismic categories tighten furtherIRC R403.1.6
Per-piece minimumAt least two bolts in every plate section, with one bolt within 12 in. — but no closer than seven bolt diameters — of each endIRC R403.1.6
Nuts & washersBolts fitted with nuts and washers; seismic design categories D0–D2 require 3 in. × 3 in. × 0.229 in. plate washersIRC R602.11.1
Sill materialPlates in contact with concrete are preservative-treated or naturally durable wood, with a foam sill sealer allowed beneathIRC R317.1
AlternativesApproved anchor straps and, for interior non-braced walls, post-installed anchors per their evaluation reportIRC R403.1.6

Worth knowing

  • Wet-set bolts drifted out of position are the norm on real pours — epoxy or wedge anchors per an ICC-ES report are the standard fix, at the report’s embedment, not the wet-set number.
  • A plate splice with one bolt serving two plate ends violates the two-per-piece rule — short closet walls catch this constantly.
  • In SDC D territory (much of California, parts of the mountain West), the square plate washers are not optional and inspectors look for them specifically.
  • Bolts through the plate’s edge third instead of the middle third lose most of their lateral value — layout before the pour beats drilling after.
Sections cite the 2021 International Residential Code and 2023 National Electrical Code as model standards. This is BuildSpec’s own summary — not ICC or NFPA text; read the authoritative language at codes.iccsafe.org. Your state may be on a different edition with amendments — check your jurisdiction page or get an Address Report.
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