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What size anchor bolts do I need to attach the sill plate to the foundation?

Answered by Brett Kulina ~ April 18, 2013 ~ No Comments » | Respond to this question

We're building a house and I'm buying things as I go. I now need to purchase the sill anchor bolts. The code calls for 1/2" anchor bolts but it doesn't specify the length. The foundation will be a crawl space and four runs high. Also for the footings it calls for number 4 rebar. Is number 4 considered 1/2-inch?

JJ Guitar - Virginia

Brett Kulina

Thanks for your question JJ, and although my answer is based on the current IRC(International Residential Code), make sure to compare this information with your specific local codes in Virginia.

The IRC stipulates that anchor bolts need to be embedded into the concrete a minimum of seven inches, but keep in mind that you need at least 2-3 inches protruding from the concrete to accommodate the pressure treated sill plate, as well as a plate washer and a nut. This means that you'll need to use 10-inch long anchor bolts to securely attach the sill plate to the concrete stem wall. Likewise, the IRC states that anchor bolts should be positioned 6-feet on center, with a minimum of at least 2 anchor bolts per plate section. There must also be an anchor bolt within 12-inches of the ends of every plate section.

Yes, #4 rebar is 1/2-inch in diameter (don't be confused by USA-made #4 rebar that is marked with the number "13"). When trying to determine the size of a given stick of rebar, remember that the rebar size number corresponds to the eighths of an inch in diameter (such as, #4 rebar is 4/8" [read 1/2"] in diameter OR #8 rebar is 8/8" [read 1"] in diameter).

Throughout your building project you will probably need to consult the IRC and your local code book often, so you may want to purchase an illustrated code check book and keep it on site for quick reference. Good luck with your home building project.

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