How would you handle this sagging notched 2x10 joist?

Question

My 1952 ranch has a saggy spot in the floor. It's centered on a vent that was cut into the top of the 2x10 joist.

The cut is about 12" wide, 5" deep. There is about 4.5" of joist height remaining below the vent, and in the middle of that section is a big knot! Adding to this dysfunction - a non-load bearing wall sits right on top of and parallel to this joist.

I should be able to get the HVAC duct pieces out of the way enough to get a jack and sister in place. A sister 2x10 would have to be spaced out away from the original joist to accommodate the vent that protrudes to the left of the notch.

Or should I use a piece of steel angle? I see some joist repair plate products for sale online, but nothing with the width required to bridge this gap.

Any tips from those with experience?

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Answer 1

For a floor joist like this with redundancy from other joists, I would sister a 6 ft chunk of 2x10 centered over the notch. Install a 6ft long spacer first, though, to avoid the duct interference. Use an adhesive to join everything, with screws drawing things tight for a thin glue line.

Ideally you would use a low-creep adhesive like resorcinol. Because of the low stress levels, low humidity, and redundancy from other joists, I might settle for a PVA glue like Titebond. I expect that the "waterproof" Titebond III has the best creep characteristics of any PVA, so that would be the stuff I would use if not resorcinol or epoxy.

Before gluing everything, you want to use a jack or wedge to remove the sag from the joist. Avoid hydraulic jacks to avoid possible pressure bleeding overnight. Remember that the joist will deflect after you remove shoring, so push it up a little too far to compensate.

Note: This is what I would do. If you hired a contractor to fix this, then he would need to obtain a permission slip from an engineer to follow this proposal. I'm skeptical that an engineer would provide this permission slip. Rather than get permission, this hypothetical contractor would sister the full joist length to stay in conformance with IRC prescriptions. That solution avoids the cost and lost time of involving an engineer. (The engineer would probably follow @isherwood and provide a mechanical fastener schedule.)