Sister Full Length Joists Instead of New Beam 1

[SarBear]

Hi everyone, I've got a situation here with a proposed fix that I'm curious if anyone has some input on. I have posted a picture below of the second floor framing plan for a home that is going to be remodeled. The two bubbled walls are to be removed to open up the kitchen. When I was at the home I discovered that the joists over one of the walls break rather than running continuous over the wall (shown below). However, the joists over the beam and the other wall run continuous without breaking. The obvious solution would be to put in a big steel beam that spans across the new open kitchen, but doing so is not feasible on this project.

My question is what if we sister some new, full-length joists to the existing joists instead of putting in a beam? The span from the back of the home to the garage wall is only about 17'-6" which is easily doable for an 11 7/8" joist. I'm not sure why they didn't do that in the first place, but here we are. Has anyone done this before? Any suggestions or concerns?

 

[jerseyshore]

I don't even think you need to attach them, just put them up next to the existing ones.

Usually the challenge when sistering or adding full length pieces into an existing space is just how do they get them in there. If a joist has bearing at one or both ends, it needs to be longer than the clear span opening so it can become a challenge just to physically get the piece up and over and into place.

 

[BAretired]

Usually the challenge when sistering or adding full length pieces into an existing space is just how do they get them in there.

That would be my concern.

 

[wrantler]

Can you nail reinforcing to the flange or web of these joists.

 

[EdStainless]

Since some of the existing joists are not continuous the added ones would need to be fastened in order to carry the load.
You might even think about a partial on the other side from the sister in the vicinity of the break.

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P.E. Metallurgy, consulting work welcomed

 

[oldrunner]

Just sister on each side without going to the support. Make sure you have enough fasteners to transfer the end shear to the original joist and check the main joist for adequate shear capacity.

 

[SarBear]

Thank you all for your thoughts.

Just sister on each side without going to the support

This solution would be amazing, but it also makes me queasy just thinking about it. The new joist would be transferring the bending and shear load back into the two separate existing joists and I'm not sure how that kind of connection could even be calculated. Sistering to an existing full length joist that has a notch or crack or something makes sense to me, but in this case where the existing joists fully break over the wall with a 1.5" gap between the ends...I don't see how anything but a new full-length joist that bears on the wall at each end would be acceptable. I'm open to to your idea because it would be awesome if I could get it to work, but I don't think I understand it well enough to be comfortable with it.

 

[jerseyshore]

What bending moment at the end of the joist? It's just shear as oldrunner highlights above.

 

[BAretired]

It might be easier to remove the deck and place new joists in from the top, then replace the deck.

 

[SE2607]

For the longest time I was anti-sistering (reinforcing existing joists with new ones that don't bear on the supports) because I wasn't confident how the load gets into and out of the sistered joist. Recently, I modeled such a condition in RISA 3D. I attached the joist with common nodes at 12". It worked beautifully.

If you are able to run full length joists and get bearing at each end, that would be great. I would fasten the new joist to the existing joist because I'm assuming you cannot attach the new joist to the floor sheathing. This way, you are using the existing (broken or cut) joist only to transfer the load from the sheathing to the new joist.

 

[Enable]

Also as an FYI for sistering the full length you'll need to accommodate deflection in the existing floor. Since the middle will likely have sagged some amount (1/2" to 1" maybe for this span) the deflected part of the floor will hit the top of your new joist first and at the ends your new joist will sit lower than the wall. Some options are to A) sister with a joist that's smaller than the deflection amount and block up to sheathing (or do nothing), B) sister with joist that's same size as existing and plane the mid section as needed or C) jack existing / bash new sister into place at ends. Option A) has the advantage of allowing you some more manoeuvrability to get the joist into the cavity as well.

jerseyshore there's no bending moment at the intermediate wall now but as soon as he removes it there better darn well be a bending moment capacity to the joist at that location (it's in the third of the span now!!). Whatever detail he runs with has to be able to transfer moment at that location. NVM you were talking about the actual end of the joist...more coffee Enable!

 

[jerseyshore]

I agree with Enable, maybe you specify 11 1/4 LVL's instead of 11 7/8" TJI's to make it easier to get them in here. I don't think most people would want to take the risk of collateral damage by just jacking a small portion of existing framing unless the house is under a big reno and it'll take a lot of bashing to get a new long 11 7/8" I-joist in there (not that the framers would care cause they'll bash anything!).

 

[SlideRuleEra]

Sistering another beam to the existing "joists" will be difficult... be cause the "joists" are actually I-Joists. The OP's detail shows the connection through the 3/8"+ OSB web... I would not rely on that for significant loads:

Instead, I would check to see if adding plywood plates to the sides of the existing I-Joists (creating a box beam) would be an adequate splice and bridge the 1 1/2" gap between the ends of the I-Joists. My preliminary calcs indicate this will work... if tributary area for each I-Joist is "small" (which it probably is).

Advantages:
No new "joists" required.
With staged demolition, splices can be installed before the wall is removed.
Decreased floor deflection.

 

[jayrod12]

You mention adding a beam to replace the wall isn't possible on this project. Can we entertain this option, or work on eliminating it, a little more?

I ask because, it would likely be far cheaper and faster to cut each of those i-joists, that are already cut, back enough to slide and LVL beam into there and use face mount hangers to support the joists on the beam. I'm scaling, but it looks like that beam span would need to be about 14-15 feet. That doesn't seem unmanageable for a reasonable depth LVL beam.

 

[XR250]

Instead, I would check to see if adding plywood plates to the sides of the existing I-Joists (creating a box beam) would be an adequate splice and bridge the 1 1/2" gap between the ends of the I-Joists. My preliminary calcs indicate this will work... if tributary area for each I-Joist is "small" (which it probably is).

I feel like nailing into the edge of the I-joist flange is sketchy at best. I do not like i-joists for many reasons but this is the main one - they suck for remodels. I would do a full length one next to the existing as JS mentioned. If it is a 2x4 wall, you could cut it 3 1/2" short and still get 1 3/4" bearing at each end - which should be sufficient.

 

[BAretired]

I believe removal of the deck and joists, then inserting new joists from the top is the simplest and best.

 

[jerseyshore]

I agree XR, I never want to nail into the edge of an TJI flange.

BA, this is probably the easiest in theory, but who is demoing the entire 2nd floor of their house for new joists?

 

[BAretired]

BA, this is probably the easiest in theory, but who is demoing the entire 2nd floor of their house for new joists?

The "entire second floor" is an inaccuracy. I count eleven joists. It is too bad they were not made continuous in the first place, but that cannot be helped.

Do it right or leave the bearing wall where it is.

 

[phamENG]

A couple important things missing from this discussion:

1) What is the foundation under the wall you're proposing to turn into a bearing wall. Granted, it's probably got some load on it now, but you'll be increasing the load on it by quite a lot. Looks like you're putting at least 845plf into that wall - it'll need something beneath it.

2) What is the uplift capacity of any connectors to the "Existing Beam in Garage"? Pull the current supports out, bending moment in the joists will increase as the span increases and the second span will be less than a quarter of the main span. The uplift force could be enough to damage the connection to that beam. I estimate about 450lbs of uplift for full live load on the long span.

What size 11.875" I-Joists are these? Yes, some heavy ones can manage these spans, but not all of them. You're flirting with the line between a floor that meets the minimum building code and a floor that is comfortable to walk on. With long spans, a code minimum floor is a nuisance with lots of vibrations - even if you can't feel it, you'll hear stuff rattling as you walk. After all, you can't guarantee that the existing floor is glued down, and if that's a big and wide open space it'll vibrate like crazy. If there are bearing walls, it gets harder to make the joists work for strength.

If we're not doing a beam, I'm in the LVL camp. Fill one side of each of the existing joist webs with OSB/plywood of appropriate thickness. Get LVLs in there - you might be able to do a 'fire cut' at one end to allow them to insert it onto the bearing wall and then rotate it up and into place to fasten to the beam in garage. Of course, shoring while doing that will be interesting. They may need to remove finishes from the exterior and insert them from outside.

Regarding the beam...I'm assuming you say it can't be done because the joists don't all break on a line, correct? Three ways around that:

1) Install one beam (probably in line with the wall to be removed on the left side of your plan above) across the whole space. Then you install new joists over the bathroom that are only half length.

2) Install two beams, one along each line. This has the advantage of splitting up the load and helping you keep depths more reasonable if needed (but again, be careful with vibrations!)

3) This one is hardly worth mentioning, but you could install a beam parallel to the joists with a beam along each wall line that is being removed.

 

[jayrod12]

OP, is only the two walls you highlighted getting removed? Or are all walls in that area getting removed and you only just bubbled the load-bearing ones?

Because that's substantially different. When I have a client asking for stuff like this, I'm usually able to talk them into putting a post somewhere down at the corner of the massive island they're likely planning. Then I tell them to frame the post out a little bigger and put your light switches and maybe a couple of outlets on the post for charging phones or using appliances. That usually let's me sell them on a post to keep the beam size reasonable.