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The 2nd floor 2x6 ceiling joists of my (I believe) 1905 house run into the eaves (24" soffit, no subfascia). Some of the ends are rotten. What I want to do is sister on 2x6s to these joists (and then add subfascia, the outside face of which will probably be where the old joists ended). I'll be cutting off the rot, maybe 6" worth at the most, so the cantilever on the sistered joists will be small.

Seems like there should be some cantilever length to total board length rule, right? How far back into the house do I need to run these 2x6s, or can I just run them to the bear on the exterior wall top plate?

Secondly, You will note in the attached pics that the rafters, which don't always land on a joist, landed on a 1x6 plate that ran along the tops of the joists, pretty crazy huh? This plate is rotten in places too and my solution has been to add what I called a 2x4 ledger (or maybe it's a plate) that runs across the tops of the joists and supports the rafters. I'm imagining this will be sufficient but... maybe I should sister on to the rafters as well and then tie them into the subfascia. If so, how long should they be?

House is in SC so minimal snow load, if that matters.

existing

planned

isherwood
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Carsten Almskaar
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1 Answers1

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The general rule of thumb for cantilevers is 3:1. However, this isn't really a cantilever situation if you're also moving rafter support. Subfascia doesn't carry load to speak of, so you're really just replacing joist tails. If the blocks are fastened well enough to the remaining joist there shouldn't be a problem, but don't make them too short. I'd lap the wall plate or butt into the new rafter support. (They don't bear there because they carry no load there.)

Regarding the rafters, I'd do as you have planned, putting the new sleeper directly over the wall. This entirely eliminates the cantilever concern in the ceiling joists and moves it to the rafters, which will carry fine if they're solid. You could put a pair of two-by boards on edge with your roof slope cut into the tops--that's often easier than trying to cut a low slope into a flat board.

isherwood
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