How to Install Anchor Bolts in Wood | Sill Plate Guide

Anchor bolts in wood typically means securing a wood sill plate to a concrete or masonry foundation using 1/2-inch bolts embedded at least 7 inches.

If you’re asking how to install anchor bolts in wood, the phrase usually refers to fastening a wood sill plate or sole plate to a concrete foundation — not joining two pieces of lumber. The standard approach is to cast the bolts into wet concrete before it sets, then slide the pressure-treated plate over the protruding threads and tighten a washer and nut on top. For existing slabs, a retrofit anchor may work, but the rules change. This guide covers the code requirements, the step order, and the mistakes that cause inspectors to flag the work.

What The IRC Says About Anchor Bolts For Sill Plates

The American Wood Council points to IRC Section R403.1.6 for the anchorage requirements that apply to wood sill plates and wall sole plates in one- and two-family dwellings.

The AWC also notes that nuts and washers are required, though the cited summary sets no minimum washer size. If you are using an approved anchor strap or other connector, the code allows it as equivalent anchorage, but only where the local building department permits it.

How To Place Anchor Bolts In New Concrete

For new work, the bolt gets cast into the wet concrete before it cures. Mark the bolt locations on the form or layout string so they line up with the holes you will drill in the plate. Push the bolt into the concrete to the specified embedment depth — 7 inches minimum for the prescriptive IRC path — and keep the threads straight and proud of the slab. The exposed length above the concrete needs to clear the plate thickness plus the washer and nut, with a few threads showing.

Once the concrete cures, the sequence runs like this:

• Set the sill plate over the protruding bolts and seat it on the foundation.
• Slide a washer over each bolt, thread on the nut, and tighten with a wrench until the plate bears firmly on the concrete.
• Check the plate with a level before locking everything down.

If you are shopping for bolts and connectors that meet these requirements, the roundup of the best anchor bolts for wood framing covers tested options for both new pours and retrofits.

Retrofit Anchoring For Existing Foundations

When the slab is already set, you cannot cast a bolt into it. The retrofit path uses post-installed anchors such as epoxy-set threaded rod or mechanical expansion anchors. Whether these qualify depends on your local code, the anchor’s listing, and the manufacturer’s instructions. The AWC’s approved-alternatives language allows them where permitted, but it does not grant blanket approval. A code official will typically want to see the anchor’s ratings match or exceed what the prescriptive rule demands.

Drilling into a cured slab changes the procedure. You first drill the hole in the concrete with a hammer drill and carbide bit, clean the hole thoroughly, then set the anchor per the manufacturer’s directions. Simpson Strong-Tie maintains a product installer’s guide with the specific steps for the connectors they make; that guide is the reference to follow when the anchor comes from a supplier with such documentation.

Common Anchor Bolt Mistakes To Avoid

Four errors show up repeatedly on jobsites, and all four can trigger a correction notice from an inspector.

• Drilling the wood too tight. A snug hole splits the plate as the wood expands or the bolt shifts. The 1 to 2 mm oversize is intentional.
• Ignoring end distances. A bolt at 2 inches from the end fails the 12-inch rule. Measure from the plate end, not from the first hole you drilled.
• Widening the spacing. Bolts at 7 feet on center miss the 6-foot maximum. And a plate section with one bolt fails the two-bolt minimum.
• Substituting anchors without approval. Code-approved alternatives must be installed per their listing and manufacturer instructions. A random wedge anchor from a hardware bin is not automatically equivalent.

Higher seismic and wind zones add requirements beyond the prescriptive baseline. The local amendment for your area controls, so check with the building department before you pour or drill.