Oversized Plumber’s Hole in Wet Floor Joists
On a two-story addition, the approved plan calls for 2x10 SPF No. 2 floor joists at 16 in. on center, spanning 14 ft 8 in. from the foundation sill to a built-up center girder; the plan notes this is the maximum span. The joists were delivered three weeks ago and stored flat on blocking over bare soil with a tarp draped over the top. A moisture meter now reads 22–26% near the top edge and 17–19% near the bottom. The plumber has cut a 3½ in. hole through one joist centered 4 ft from the sill and has notched the top edge 1¼ in. deep by 3 in. long at midspan to clear a drain line. The framer wants to install the subfloor tomorrow, glue and screw it, and let the HVAC dry the house out. The owner is worried about squeaks and drywall cracks.
1. Evaluate the plumber’s hole and notch against common prescriptive limits and the structural role of the joist. State whether you would accept the work, and describe a repair that does not require replacing the full joist.
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2x10 nominal is 9¼ in. deep. The hole is 3½ in., or 38% of depth; the usual prescriptive limit is one-third (about 3 1/16 in.), so the hole is oversized. It is centered 4 ft from the sill on a 14 ft 8 in. span, outside the middle third, which helps, but an oversized hole still removes section near the neutral axis and can start a splitting failure. The notch is 1¼ in. deep, about 13.5% of depth, which is under the one-sixth depth limit (about 1.54 in.), and 3 in. long, just under the one-third depth length limit (about 3.08 in.). A top-edge notch at midspan is on the compression side, but combining a notch and an oversized hole 4 ft away in a joist that is also wet makes acceptance risky. I would reject the hole as cut. Repair by replacing that joist, or by installing a full-length same-size sister of equal or better grade, glued and nailed or screwed to the existing joist and bearing at both ends; a short scab is not adequate to restore the section. Have the plumber reroute or use a smaller line; if a hole is unavoidable, keep it within one-third depth, at least 2 in. from edges, and outside the middle third.
2. Explain what the moisture readings mean for the floor assembly, what will happen if the framer closes it in tomorrow, and what acceptance and drying steps you would require before subfloor installation.
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The readings show the joists are not dry enough to close. The top edge is wetter than the bottom, so the joist is already drying differentially; as the top edge loses moisture it will shrink more than the bottom, tending to cup or crown the joist. If the subfloor is glued and screwed now, the glue line will be stressed as the joist shrinks, and the finished floor and drywall above will move with it-squeaks, nail pops, and cracks are likely. For dimensional lumber, frame at or below about 19% MC, and ideally near 15% or the expected in-service moisture content; 22–26% is too high. I would not install the subfloor tomorrow. Remove the tarp, separate and sticker the joists if possible, and use fans or dehumidification, or wait for stable readings. Take readings at multiple points on each joist; require the high readings to come down and stabilize, not just the average. Do not rely on the HVAC to dry the frame after it is closed; the assembly will be trapped.