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Sill plate anchor bolt question

Debra_Ann | Posted in General Questions on

I’ve run into a sill plate anchor bolt issue, and I could use some suggestions. My main entrance needs to be handicapped accessible (no step entry). The doorway sets well back underneath an 11 foot square porch roof. The porch floor is only about 18″ above ground level, and we are planning to pour concrete for it. (I’m highly allergic to mold that often forms under low-lying wood porches, so that isn’t an option for me.)

I’m planning on raising the concrete house foundation higher along the porch, and hanging the wood floor joists behind it. This would leave just the treated sill plate and subfloor behind the flashing (peel and stick water barrier, plus galvanized metal sheet and rigid foam expansion joint) between the concrete porch and the house. Plus I plan on installing a rigid sill pan for the door.

BUT the sill plate anchor bolts would stick up higher than the subfloor (instead of normally sitting between floor joists). I imagine we can space the anchor bolts so they wouldn’t be placed inside the doorway, but is it OK to drill holes in the subfloor and possibly the wall base plates to make room for the anchor bolts along the wall by the porch?

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  1. GBA Editor
    Martin Holladay | | #1

    Your question is confusing (at least to me).

    When choosing anchor bolt locations, no one ever puts an anchor bolt at a doorway.

    Assuming that your anchor bolts aren't at a doorway, the portion of the bolt that extends above the concrete will be between studs (hidden in the wall). What's the problem?

  2. Expert Member
    Michael Maines | | #2

    When anchor bolts are placed in doorways (it happens, including recently at a walk-out basement on one of my jobs) you just cut the bolt off, and if necessary add a Simpson Titen HD or similar screw-in concrete anchor next to the doorway. It's not uncommon for contractors to counter-bore anchor bolt washers and nuts, but it greatly reduces their effectiveness and does not meet code.

  3. GBA Editor
    Martin Holladay | | #3

    You're right, of course. Anchor bolts are sometimes placed in doorways.

    My statement -- "No one ever puts an anchor bolt at a doorway" -- was inaccurate.

    I should have written, "Unless the concrete contractor makes a mistake because he can't read the plans, no one every puts an anchor bolt at a doorway."

  4. Debra_Ann | | #4

    Let me try clarifying this. The foundation is a conditioned crawl space, with poured concrete walls. The concrete foundation wall next to the porch will be elevated, in order to protect the wood joists from moisture at the junction with the concrete porch.

    So, along that section, the sill plate will be bolted to the concrete, then the subfloor directly on top of the sill, then the wall frame on top of that. But the bolts, washers, and nuts will be sticking up where the subfloor and wall need to sit on the sill plate.

    Will holes need to be created in the subfloor and bottom wall plate to make room for the bolts/nuts, and allow the subfloor and wall to sit flat on the sill? And if so, is that allowed in the code?

  5. GBA Editor
    Martin Holladay | | #5

    Cut off the tops of the anchor bolts flush with the top of the nut with a Sawzall. Drill holes in the subfloor at anchor bolt locations. Mark the bottom plates of the walls to indicate bolt locations, and drill the underside of the bottom plates with a 1-inch bit (not all the way through the bottom plate -- just enough to accommodate the protrusions).

    As far as I know, all of those steps will work -- without violating code.

  6. Expert Member
    Michael Maines | | #6

    Edit: overlapped with Martin.

  7. Debra_Ann | | #7


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