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Anchor Bolts

Written for Canada. Plans are metric, but many crews and suppliers work in feet and inches, so this site gives both: millimetres and metres, with feet and inches beside them. Codes are the National Building Code of Canada 2020 (NBC 2020) Part 9 as your province adopts it. A number marked Confirm has not been checked against every province, so check it with your own authority before you act on it.

Reviewed by a working tradesman with 17+ years in the field.

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Bolts tie the frame to the concrete. Size and spacing come from your code or drawings.

I am a:

Tap your level and the boxes below open to the advice for you. Remembered on this device.

What it isSteel bolts set in the concrete that tie the wood sill plate, and so the frame, to the foundation.
Your jobSet the bolts where the code or drawings say, at the right height and plumb, before the concrete stiffens.
The hard ruleSize, spacing and embedment come from your code or the drawings, never a US guide. Cap exposed threads.
The checkCount, spacing, embedment, plumb, height and threads, before the pour is finished.

By the end you can

  • Say what the anchor bolt rules in Part 9 cover.
  • Name the types of anchor and when each is used.
  • Set cast-in bolts and protect the threads.
  • Count bolts for a wall and check layout.
Stop and read

Exposed threads are a hazard. Bolts and rods stick up out of the concrete at hip or knee height and can cause impalement injuries and trips. Cap them where people work or walk, and take care on your hands and knees around them.

Structural work is not guesswork. Size, spacing, embedment and hold-down hardware come from the code or the structural drawings. If the drawings give a number, the drawings win. If you are not sure, ask the engineer before the pour, because a missed anchor costs far more to fix afterward.

The big idea

Anchor bolts tie the wood frame to the concrete. They resist wind trying to slide or lift the building and, in earthquake country, sideways shaking. A bolt that is missing or badly placed is one of the most expensive things to fix after a pour.

What the code says

From Part 9, Article 9.23.6.1, as printed in the Vancouver Building Bylaw 2014 (a municipal reprint, possibly older than your province's edition; I read it through a summarising tool, so check the exact wording in your own code):

  • Standard: fasten the sill plate to the foundation with anchor bolts not less than 12.7 mm (1/2 in) in diameter, spaced not more than 2.4 m (7 ft 10 1/2 in) o.c. Embedding the ends of the first floor joists in concrete is the other option.
  • Two or more floors where seismic or wind loads are higher (Sa(0.2) at least 0.70 but not above 1.2, or hourly wind pressure at least 0.80 kPa but not above 1.20 kPa): at least two bolts per braced wall panel, and either bolts of at least 15.9 mm (5/8 in) within 0.5 m (1 ft 7 3/4 in) of the end of the foundation at not more than 2.4 m o.c., or 12.7 mm (1/2 in) bolts within 0.5 m of the end at not more than 1.7 m (5 ft 7 in) o.c.
  • Installation: bolts are fastened to the plate with nuts and washers, embedded not less than 100 mm (4 in) in the foundation, and designed so they can be tightened without being withdrawn.
  • Higher still (Sa(0.2) above 1.2, or wind pressure of 1.2 kPa or more): anchorage is designed under Part 4, which means engineered drawings.

The washer size and edge distances were not given in what I read. Take them from the drawings or your code.

Types of anchor

  • Cast-in-place bolts (J-bolts, L-bolts, or bolts with a plate or head). Set in wet concrete. The usual choice for new work.
  • Post-installed mechanical anchors (wedge, sleeve or screw). Installed into hardened concrete, for corrections and retrofits.
  • Adhesive (epoxy) anchors. A threaded rod set in epoxy in a drilled hole. See Epoxy Anchors.
  • Hold-down anchors. Heavier anchors that tie shear wall ends to the foundation. See Hold-Downs.

Setting cast-in-place bolts

  1. Lay out. Mark bolt locations from the plans before the pour and check them against door openings and anything that comes through the wall.
  2. Use a template. A template or form-mounted guide puts the threads where the plate holes need to be.
  3. Set while plastic. Place bolts after screeding and before the concrete stiffens, plumb and at the right height.
  4. Protect threads. Wrap or cap them so concrete does not stick.
  5. Mind the edges. Keep clear of edges and other anchors by the distances the design gives.
  6. Re-check. Check position and height again after finishing, while you can still move them.

Use the washers the code or drawings call for and tighten snug, then to the specification. Over-tightening crushes the plate; under-tightening leaves it loose. For treated lumber, use hardware the maker lists for it (hot-dip galvanized or stainless).

Worked example

Numbers made up. A wall 9.6 m (31 ft 6 in) long, bolts at 2.4 m (7 ft 10 1/2 in) o.c.: 9.6 ÷ 2.4 = 4 spaces, so 5 bolts counting both ends. If the higher-load option applies and bolts go at 1.7 m (5 ft 7 in) o.c.: 9.6 ÷ 1.7 = 5.65, so round up to 6 spaces and 7 bolts. Always check where the code wants the end bolts and the drawings for the real count.

Common mistakes

  • Spacing or embedment from a US guide instead of your code
  • Bolts out of plumb or too low
  • Threads coated in concrete
  • Wrong washer or nut
  • A post-installed anchor in cracked or too-young concrete
  • Forgetting anchors shown on the drawings
Pro note

A bolt 10 mm (3/8 in) off can sometimes be bent a little or its hole slotted, but only if the engineer or code allows it. Do not bend a cast-in bolt without asking. Better to place it right.

Weather note

Cold concrete sets slowly, so re-check bolts after finishing. Hot, windy weather stiffens it fast, so set the bolts early. Rain in drilled holes ruins post-installed anchors.

What the inspector looks at

Bolt size, spacing, embedment and washers against the plans or code, before the sill goes on. Confirm what your building department checks.

✅ Check yourselfTap a question
In the Part 9 text I read, what is the standard minimum bolt and maximum spacing for fastening a sill plate?
Not less than 12.7 mm (1/2 in) diameter anchor bolts spaced not more than 2.4 m (7 ft 10 1/2 in) o.c. (Sentence 9.23.6.1.(2), as printed in a BC municipal reprint). Check your edition.
How deep must the bolts be embedded?
Not less than 100 mm (4 in) in the foundation, fastened to the plate with nuts and washers, and designed so they can be tightened without being withdrawn (Sentence 9.23.6.1.(4)).
A wall is 9.6 m (31 ft 6 in) long. How many bolts at 2.4 m o.c.?
9.6 ÷ 2.4 = 4 spaces, so 5 bolts counting both ends. At 1.7 m (5 ft 7 in) it is 9.6 ÷ 1.7 = 5.65, so 6 spaces and 7 bolts. Lengths are made up. Check where the code wants the end bolts.
Who wins if the drawings and a general guide disagree?
The drawings and the code for your project. Never use numbers from a US guide.
Why cap exposed threads?
Threads standing out of concrete are an impalement and trip hazard, and caps also keep them clean.
A bolt is 10 mm off after the pour. Do you bend it?
Not without asking. Bending or slotting is allowed only if the engineer or code allows it.
🧰 Gear for this stepMust-haveRent itNice to have
  • Must-haveLayout:
  • Must-haveSetting bolts:
  • Must-haveProtecting threads: caps, tape or wraps; rebar caps on exposed threads where people walk
  • Must-haveAnchors: cast-in J-bolts or L-bolts with nuts and washers as the drawings list; hot-dip galvanized or stainless where in contact with treated lumber
  • Rent itPost-installed work:
  • Must-havePPE:
  • Must-haveDust: respirator (CSA Z94.4) when drilling concrete, with a vacuum or wet method for dust control
👷 Who can do thisTap your level
Home DIY
A capable owner can lay out and set cast-in bolts for a small shed or deck slab when the drawings give the size and spacing. Do not guess on a house, a seismic or high-wind site, or hold-downs: the plans or an engineer decide. Do not drill concrete without dust extraction or wet drilling; a dust mask does not control silica.
Laborer or helper
Carry bolts and templates, clear the forms and keep clear of the pour. Do not move, bend or cut a bolt on your own. Tell the lead if a bolt is out of position, bent or missing before the concrete goes in.
1st-year apprentice
Set bolts from a template, check height and plumb, and protect threads under supervision. Learn to read anchor details and why a missed bolt costs more after the pour.
Apprentice, 2nd to 4th year
Set bolts from the template, check height and plumb, and protect the threads under direction. Do not drill cured concrete without dust control. Report any bolt that looks out of position before the pour.
Journeyperson
You own bolt layout, position and height checks before the pour, and the order of nuts and washers. Stop the pour if the count or positions do not match the drawings.
Lead hand or foreman
Check layout against the drawings and the code before the pour, and sign off the bolt count. Decide when a missed or wrong bolt goes to the engineer.
Contractor or business owner
Price bolts, templates, caps and a re-check before the pour. Keep photos of the bolts in place and the inspection record. Ask your lawyer or insurer who carries the cost of a missed anchor.
Starting a new business
Know the anchorage clause in your province's code and when an engineer's design replaces it. Keep the inspection record and photos, and ask your insurer about structural claims.
By Province:

Each province adopts its own edition of the National Building Code and may change the anchorage rules. The loads that decide which option applies (Sa(0.2) and hourly wind pressure) depend on your location. I dropped the old per-province list because I could not verify it. Confirm with your building department, and follow the drawings if they are stricter.

See Canada by Province for the full comparison.

Sources:
  • Vancouver Building Bylaw 2014, Part 9, Article 9.23.6 (municipal reprint of NBC Part 9; read through a summary, so confirm the wording; Articles 9.23.6.1 and 9.23.6.3)
  • Washer sizes, edge distances, post-installed anchor ratings and provincial rules were not verified. Bolt counts are calculated and re-checked.

Last reviewed October 2026. General information, not engineering or legal advice.

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