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I'm looking up information about temporarily supporting a ceiling to make an opening in an interior load bearing wall. Wooden stud and joist framed house. For the most part, the materials that I'm seeing (like this This Old House video on YouTube) show the supports being put up on only one side of the wall.

That seems like it would only hold up the joists on one side of the wall. Why is this sufficient?

Note: The wall runs down the center-line of the house. The joists end at the top plate and don't overshoot it by more than an inch or two. The house in the video has the same layout and build scheme (same materials, structure, etc) as mine. The carpenter in the video is from around here so he would understand the house pretty well.

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    It will depend on the build. Most load bearing walls are in the centre of the joists, so one side is enough. If the joists meet on top, then you might need both sides supported.
    – crip659
    Oct 16, 2023 at 14:36
  • @crip659 The joists end on top of the wall, both in my house and the one in the video. Tommy (the guy in the video) is familiar with the build of the house but seems to shore up the ceiling on one side only anyway. See note above. Oct 16, 2023 at 14:57
  • If your ceiling support is perpendicular to the joists, the support basically (temporarily) replaces the wall.
    – Huesmann
    Oct 17, 2023 at 13:11

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Often, the joists extend across the supporting wall rather than ending at it. In that case, any support on the other side of the wall would be redundant, as the joist is already supported nearby.

If the joists really do end at the wall, they would almost certainly be staggered, as could be determined by checking whether the joists on each side of the wall perfectly align with each other.

On the other hand, they might butt against each other, in which case they would need supporting on both sides.

The people in the video likely knew how the joists were installed (either one long joist, or overlapping joist ends that are well secured to each other), and so knew that it was appropriate not to support the other side.

But if in doubt, play it safe and potentially waste some effort supporting both sides.

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  • The joists do end at this wall. If you mean they don't butt up end to end, yes, they are staggered. Why is that significant? Oct 16, 2023 at 14:55
  • @aquaticapetheory If they are staggered, then a good chance they are nailed/screwed to each other. The nails should hold enough for temporary use/limited time. Butt joints will not have enough hold.
    – crip659
    Oct 16, 2023 at 15:04
  • @aquaticapetheory - that means that the header the joists sit on support the joists just fine, so adding the additional support only needs to be on one side to support the header.
    – Jon Custer
    Oct 16, 2023 at 15:05
  • @crip659 Gotcha. Unfortunately, I don't trust the builders to have nailed the joist overlaps. The joists may be toe-nailed to the top plates but I don't remember seeing nails in the face. Oct 16, 2023 at 15:07
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    @aquaticapetheory There is nothing saying you cannot support both sides. If you don't trust the joints, use both sides for support. It is just on most builds it is not necessary, so it saves some time if not needed.
    – crip659
    Oct 16, 2023 at 15:18
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Mr Silva must know that the joists from the opposite room will be adequately supported by his temporary structure. How they are supported, and for that matter how he knows ... is not in the video. It's a good question.

If you don't have that confidence ... if you think you have joists that end over the wall and that do not protrude past the wall at all, you can and should support on both sides.

It's easy to figure it out. A 1/2 inch hole in the ceiling and a $70 borescope will allow you to see the joist configuration and whether and how they are supported by the wall or by screws or nails into each other.

Also ... he seems capable of cutting open the wall very precisely, building the temporary support, and taking it down without doing any damage whatsoever to the ceiling. It's like he was never there. I'm not that good, are you? Because if you're going to have to paint, there's not much harm in cutting a bigger hole in the ceiling and sticking your head in.

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  • The overlapping joists are face nailed above the wall. 3-16d common nails, 4-10d box nails, or 4-3" x 0.131" nails. Another wall or roof brace from above go into the supported joists and through the temporary wall. The floor loads over the unsupported side go through the face nails.
    – popham
    Oct 16, 2023 at 22:30
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The IRC requires face nailing the joist overlaps above a bearing wall's top plate. See IRC R802.3.2. The fastening schedule is item 3 from IRC Table 602.3(1). Each connection is good for 420 pounds under Doug Fir framing according to the AWC's connection calculator.

Alternatively for butted ceiling joists, toenailing to the top plate is permitted instead. See IRC R802.3.2 again. Item 2 in IRC Table 602.3(1) specifies these toenails, where the uplift strength is 100 pounds under Doug Fir according to the AWC's Design Aid for Toenail Connections. I expect that the sum of withdrawal strengths from floor sheathing fasteners would pick up the slack for, say, a bedroom full of furniture.

The top of the temporary wall supports a cantilever that extends out to snatch up all of the load from the old partition wall. The face nails or toenails only need to support the floor loading from above the seemingly unsupported side. The rest of the load bears directly on the cantilever tip.

I'm familiar with that This Old House video. He pinches the wiring between the old top plate and the new header. There are YouTubers with better practices than This Old House. They're untrustworthy. That exact video is the one that I cite as evidence, but I recall another one.

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  • This is good information but you make hard assertions about the way something is built site unseen. My house is 70 years old, it's a mash-up of balloon and platform framing, and the builders didn't really care about the IRC. Based on all the joist overlaps I've seen, everything is toe-nailed at best. Oct 17, 2023 at 13:39
  • I also noticed that wire. I think he leaves a little space between the 2x8s in the spacer and that's where the wire rests. The more subtle problem is that ceiling is almost certainly strapped so if he doesn't happen to hit a strap, that top 2x6 is resting on plaster alone. They definitely cheat with movie magic: there's a bathroom vent install one where tape holding the duct magically transforms from cheap crap to the UL-rated stuff between shots. I take youtube video with a healthy dose of salt and picked that one because it was clean and clearly showed what I wanted. Oct 17, 2023 at 13:45
  • @aquaticapetheory, I made no assertions about the way anything is built. I made assertions about the building code's prescriptions and the corresponding strengths for two mutually exclusive alternatives. If I had said "that'll hold up 420#," then I would concede your point. You said nothing about a 70 year old structure. You provided an episode of This Old House that featured quite a new structure. This is therefore a well calibrated answer for the question you asked.
    – popham
    Oct 17, 2023 at 16:22
  • The house in the video is roughly same vintage as mine; I can tell by the layout and materials. This Old House largely deals with old houses around New England, hence the name. This answer mainly refers to code but your earlier (deleted?) comment just said that the overlaps are face-nailed. Someone that doesn't know better can get in trouble reading something like that (they shouldn't be jacking up their ceilings but that's another matter). You may want to consider adding some caveats to your answers. Oct 17, 2023 at 21:24
  • @aquaticapetheory, two alternative scenarios with widely different capacities provides plenty of nuance. This answer needs no caveats.
    – popham
    Oct 17, 2023 at 21:45

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