Set while the concrete is still soft
On a monolithic slab or the top of a foundation wall, the anchor bolts go in near the end of the pour, while the surface is still wet enough to work. The crew follows the sill layout down the edge, plumbs each bolt, and sets it to the depth the plan calls for before the final float goes on.
- Spacing and layout come off the framer's plan, not a rule of thumb
- Each bolt is set plumb, at the right height above the finished concrete
- Heavier hold-down hardware goes in at corners and beside wide openings, where the plan schedules it
Why the framing plan has to be settled before we form
If an opening moves on the plan after the pour, the hardware does not move with it. That is why we want the framing layout, the openings marked, and the hold-down schedule in hand before we form, not after we strip. A wall or an opening that shifts once the concrete has cured usually means drilling into finished work to fix it, and that costs more than waiting a week to form would have. If the plan is still moving when you call, say so. We would rather push the pour than set hardware to a layout that is about to change.
What the bolt is actually holding down
The sill plate is the first piece of wood in the whole frame, and everything built above it, the walls, the floor system, the roof, ties back down through that plate to the anchor bolts. In a wind, that connection is what keeps the building from lifting or sliding off its own foundation instead of just resting on top of it. A slab or a wall with no bolts set in it is not attached to anything below it. It is only sitting there.
On a post frame building, there is nothing to bolt down
Not every job needs them. A post frame building carries its own weight on posts set in their own individual footings, so there is no wood sill plate resting on a concrete edge and nothing to anchor. Whether a job needs anchor bolts comes from how the building is framed, not from the concrete underneath it.