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I need to attach a sill plate to a foundation that does not have anchor bolts. I'd like to use GRK Caliburn screws. The sill plate is 1.5 inches thick. How long should the screws be?

It looks like 2-3/4" is a commonly sold length. Is that sufficient?

Vebjorn Ljosa
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Anchor bolts are used to: 1) keep your house from sliding along the concrete foundation, 2) resisting the house from being peeled away from the foundation (like a zipper), or 3) keeping the house tight to the foundation so the house doesn’t float away.

  1. Your house has shear walls that need to be fastened to the foundation. I live in a high wind area so our requirement is 5/8” bolts at 24” on center. Depending on your wind loads, you’ll need sufficient anchor bolts of sufficient diameter to resist winds in your area.

  2. Shear walls keep the house square and upright, but the shear “box” could be tipped over if the corners are not anchored down. In fact, where I live 3” square washers are required to keep the plate from pulling through the head of the anchor bolt. If you live in a seismically active area like Santa Barbara, CA then theses anchors are designed to keep your house anchored to the foundation (and your foundation is designed to resist such seismic forces.)

  3. In high flood areas the wood house could float away without sufficient anchors.

All of these loads (stresses) need to be calculated or you need to use the standard Building Code requirements.

I doubt your “screws” would satisfy any of these stresses. I’d use anchor bolts.

Lee Sam
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  • Additionally I'd suggest contacting the local building department/inspector to ask them. – FreeMan Oct 14 '20 at 15:22
  • I seem to make small additional notes to a lot of your answers. Please do _not_ take this as criticism, I'm just trying to emphasize things that are probably _very_ obvious to you with your engineering background that may not be quite so obvious to the layman. I really like how you lay out your points up front, then explain them in more detail. Most of your answers end up getting a vote from me. – FreeMan Oct 14 '20 at 15:24
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    @FreeMan I enjoy reading people’s comments. Feel free to add comments...we’re all just trying to get the best recommendations to the OP. I’ve learned that there’s usually more than one way to do something. – Lee Sam Oct 14 '20 at 16:01
  • We had a few contentious comments a month or so ago, I just wanted to ensure there were no hard feelings... Life is like UNIX - there are 19 ways to skin a cat, but none of them are user friendly. :) – FreeMan Oct 14 '20 at 16:04
  • @FreeMan Oh I always think I’m right and will defend my statements to the “Nth degree”...but really I just know what’s happening in my little corner of the world. – Lee Sam Oct 14 '20 at 16:10
  • Caliburn screws are screw anchors designed for this application, as an alternative to cast-in-place anchor bolts. – Vebjorn Ljosa Oct 14 '20 at 18:33
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The report ESR-3251 from the ICC Evaluation Services evaluates GRK Calibur XL screws. The report specifies that 3-1/2" screws should be embedded at least 2.76" into the concrete, whereas 5" screws should be embedded 3.35" into the concrete.

Vebjorn Ljosa
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  • Fastening boards to concrete and fastening boards to concrete that develops hundreds of pounds of resistance is another matter. Yes, the report may recommend embedment length, but it doesn’t give shear and withdrawal values for various strengths of concrete, distance from edge of concrete, minimum spacing allowed to develop specified strengths, etc. – Lee Sam Oct 14 '20 at 19:18
  • It actually has all of those things. I fixed the link now so you can take a look if you're curious. – Vebjorn Ljosa Oct 15 '20 at 01:34
  • It appears the fasteners are used to anchor items to concrete, but not to be used as structural fasteners. (See Item 4.1, limitations.) Their example in Figure 4A and 4B shows a pipe bracket fastened to concrete ceiling. In addition, we do not know the load from your house on the concrete footings so we don’t know how many fasteners are req. It’s probably an excellent fastener for attaching heating units to concrete ceilings, etc., but they’re not allowed for structural loads. I’d use an expansion shield (it’s like an anchor bolt but can be installed after the concrete is installed). – Lee Sam Oct 15 '20 at 03:50
  • Thanks! I have some bolts and lag shields, so I can use those. – Vebjorn Ljosa Oct 17 '20 at 00:05