Anchor bolt tightness — new construction
My anchor bolts were tightened up initially with a wrench. Upon checking them a few months later, most of them were only hand-tight? On many of them you could see where the washer had indented into the sill plate, so they were apparently tight at one time. So, the question is—how tight should they be and how did they get loose?
Specifics—slab on grade, 1/2″ anchor bolts with 1 3/8″ washer, 2×6 sill plate, sill-seal vapor barrier.
My speculation is that over time, the sill-seal material crushed , or the bolts stretched , or the wood gave way to the washer, or some combination of all this. Is this a common issue? I went back and re-tightened all the bolts that I could get to.
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Replies
John, Most likely the pressure treated sill plate has simply dried out and shrunk slightly. You should retighten all of them while they are still accessible and possibly use a split lock washer which has some spring to it. Retighten at the last moment before they are concealed.
John: Throw larger, heavier washers under what you have, too.
The above answer tells you what you need to know but here is a little more detail for those that are curious. First is that the bolts MUST be tight per Building Codes. It gets a little more serious in seismic and high wind areas but they have to be tight no matter what other requirements may be out there. Treated sill plates are generally very wet and all wood shrinks more perpendicular to the grain than parallel when it dries. So this wood shrinks. The sill seal also cannot be fully compressed by the initial tightening of the bolts generally spaced 6 ft or 4 ft apart. Once the weight of the wall, floor, roof, and whatever else you put on it sits on the sill plate, everything settles in and you need to re-tighten. As noted above, ideally just before you close up the wall. Also a good time to seal the joint as sill seal does not solve all infiltration issues.