Ways to strengthen a joist.


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Old 01-08-15, 12:11 PM
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Ways to strengthen a joist.

A few years ago I tiled my kitchen floor. Before doing that I decided to strengthen my floor joists. I thought that 2x8 with an 11 foot span (from foundation to carrier beam) was a bit much for tile.

So, from the basement I did two things.

1) In the basement, 3 feet from the foundation, built a wall (the length of the kitchen--14 feet) with a double 2x8 header which was butted up to the ceiling joists (the kitchen's floor joists). This cut the span of the joists from 11 feet to 8 feet.

2) Sistered each joist with two pieces of plywood, 8 feet long and 7 inches high. These were adhered with Liquid Nails and deck screws. The boards run the length of the new 8 foot span.

The tile floor has been fine for years.

Now I am putting a bathroom in the basement and want to remove a 4 foot section ad the end of the header I created. This would take away support from 4 of the joists. I have an easy way to transfer the loads for all joists so the span will still be 8 feet or less -- except for one joist.

For this one joist, it falls about an inch or two from where I could put a stud under it. In other words, in the basement, if I put a stud up to the ceiling, I just miss the joist.

But I figure I can still secure this joist by one of the following methods.

If the stud misses by 3/4" or less:
Sister a 2' length of 2x8 and put a stud under the sister, not the joist.

If the stud misses by more than 3/4:
Take the joist and one next to it. Sister a 2x4 on the inside of each joist up at the top, near the subfloor above. Then put a 2x4 header below that, and a stud under the header. I don't think that is a very long span for a 2x4 header.

If the above is not feasible:
Fill the 14.5" between the two joists with 2x8s, all cut to about 2 feet (and some ply to make up any gap). This would create a solid block between the joists. A stud could go at any point below. Each joist could be lag bolted into the block.

I think all three of these would work. The last option might be overkill. There is no load in my kitchen with the exception of the tile floor and an island. the island is not part of this equation. It is over the area that is not being touched.

So, I may not even need to do anything in order to remove the 4 foot section of my header, but I would feel better if I did. All I want to do is cut the span of this joist.

Do any/all of the above sound reasonable?
 
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Old 01-08-15, 12:29 PM
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It sounds like the point you're starting from is as much or more than what would be used to shore up a hole being added to an original bearing wall.

If you can leave, or better yet double the end stud on the supporting wall, the doubled 2/8 top plate you've already got sounds like it'd be plenty as a replacement header for making a 4-foot gap in a bearing wall (which would normally only have 1 or 2 2x4s as a top plate with 16 inch stud spacing). If you have to remove the support all the way to the end of the 2-pc 2x8 beam, that may require some kind of remedy, but if the part that's intact were more than 8-ft then your double 2x8 may be plenty strong as a "cantilever".

Make sure you look into your local codes to see if there's anything applicable to this and hopefully one of the licensed/retired guys on this board could either confirm or correct my opinion before you build anything based on my opinion (I'm a structural analysis engineer, but work in aerospace not construction and I don't know much about code requirements especially in NY).
 
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Old 01-08-15, 02:04 PM
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I dont think what I wrote is clear. I will try again, with an example that, hopefully I wont confuse.

Lets say there is a 2x8 joist that spans 10 feet, but you want to lessen the span to 5 feet.

But, at the 5 foot mark, the stud will not be under the joist. It might be an inch or more away.

So, if it is only 3/4 of an inch away, I am thinking that I could sister a 2' length of 2x8 and put a stud under the sister, not the joist. And that would support the joist.

If the stud would fall more than that, I was thinking of taking the joist and one next to it. Sister a 2x4 on the inside of each joist up at the top, near the subfloor above. Then put a 2x4 header below that, and a stud under the header. I don't think that is a very long span for a 2x4 header. This way, the header is still recessed into the ceiling.

Or, if that would not be strong enough (although I think it would), I could fill the 14.5" between the two joists with 2x8s, all cut to about 2 feet (and some ply to make up any gap). This would create a solid block between the joists. A stud could go at any point below. Each joist could be lag bolted into the block.

Do any/all of these three options sound like good choices?
 
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Old 01-08-15, 02:37 PM
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Your question is pretty clear. You reduced an 11' span to 8'. You also supported this "new" 8' span with a header (beam) perpendicular to joists, 14' long.
I think you are saying you can still support all these joists at the 8' point except for one?
That I would do nothing, or do your idea of a sister block the same height as adjacent joist and let the wall sit on that. (option 1)
The beam you built and the measures you took to strengthen floor were above and beyond.
I'm not an engineer, but you either accomplished or are close to being able to remove a wall completely, I understand that's not your goal. I sense that is what bmgreene was saying.
 
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Old 01-08-15, 03:57 PM
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I guess I misread, I thought the plan was to open up part of the supporting wall by removing studs, but that the double 2x8 header would remain in place for the full length.

If there's no island/major appliances over the area where the wall/header needs to come out and it's just a foot traffic area, I'd imagine the original joists should be plenty strong for the loading there. If you're only looking to reinforce one joist which might not have a stud under it, probably the least precision-intensive reinforcement would be to put a couple 14.5 inch lengths of 2x8 between the joist you're worried about and the adjacent joists on either side, attached on the ends with simpson ties and glued to the subfloor with liquid nails (more to prevent creaking than for any need for a connection there) along the line in which the stud will end up located so that the top of the stud will just land anywhere along one of those cross-braces (better yet would be to put a top plate over the studs going in under that cross-bracing). Hopefully my description of that makes some sense.

Filling in the entire gap with a stack of 2-ft lengths of 2x8 shimmed in with plywood sounds like it'll add a lot of weight for the joists to carry while only increasing the strength locally in the middle, and would probably need to be cross-drilled through the whole 19.5 inch length from one joist face to the other so you could bolt the stack together with a couple lengths of all-thread (way more work than it's worth IMO).
 
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Old 01-08-15, 04:13 PM
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What exactly is happening with the new bathroom. Are you putting a wall where your new support beam is? And the joist you will be missing won't be over that wall? If so, why not extend the wall and inch or two? Or, bring the top plate over the get under the joist? Or just put a 2x8 bridge between that joist and the supported one with the bridge over the wall so it rests on it for most of its length?
 
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Old 01-08-15, 04:23 PM
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bmgreene, I'm not sure if this is what you are intending but you just made a light go off over my head.

When you say to put a few cross pieces in, my first thought was that the end grain will be facing the joints so it makes no sense. Even with the simpson ties, it would tie it all together, but I dont see how the ties would help because the middle joist of the three would be the one I want to support so the ties on that joist really wouldnt do more than hand the cross pieces.

But, then I realized (unless I'm wrong or maybe this is your point) that I dont really need to support the joist itself. If I support the floor between the joists, then the joist cant move. Is that correct and is that what you meant?
 
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Old 01-08-15, 04:34 PM
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drooplug,

Are you putting a wall where your new support beam is? And the joist you will be missing won't be over that wall?
Exactly, it misses by an inch or two.

If so, why not extend the wall and inch or two?
Just based on the layout, it just doesnt work. the wall I am building is actually a short extension of an area with two closets. The extension is really only going to be 6 inches or so and will be the studs for the bathroom door. Extending the wall wouldnt look right to me.

Or, bring the top plate over the get under the joist?
If I understand, then the plate would hang down and I need to solution to be recessed.

Or just put a 2x8 bridge between that joist and the supported one with the bridge over the wall so it rests on it for most of its length?
Hmmm. this might be a way to go. I think this is what bmgreene mentioned. The only concerns I have here that I am supporting the floor more than the joist--but I guess that is just as good.

I think I might agree with Handyone though, and I wonder if option 1 is the best. Although I could mix option 1 and the bridge. Probably overkill, but not much time/effort.
 
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Old 01-08-15, 05:05 PM
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really if you've just got foot traffic over that patch of floor you shouldn't need extra reinforcement, the reinforcement you did originally was probably overkill for anything short of trying to dig a basement under a garage, and removing that extra support from one joist only would only present any kind of risk if it were maybe the one under the island (and even then probably wouldn't actually be a problem). I'd only really worry if you were undercutting support from a bearing wall on the level above, but that's not the case since what you're removing wasn't really a bearing wall to begin with (even if it was build stronger than one...)

The cross-bracing would still ultimately be bracing the joist first and the subfloor second, a couple simpson ties (the L-bracket type, one on either side of the brace) would be more than strong enough for such light duty and would give you some connection between the joist and the stud without adding a ton of extra weight. Ideally it would be stronger to use joist hangers, but you'd have to tear up the flooring/subfloor above to do that, and it's not worth that much effort for what support you really need. If possible, having a 2x4 top plate for whatever is going in run across under the line of the bracing and at least extending across the joist would be ideal, but I'd imagine that if you could do that then you wouldn't have the problem of not getting a stud under the joist to begin with; but perhaps some kind of gusset/filigree could be extended past the end of the wall to give some bit of connection?
 
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Old 01-08-15, 05:39 PM
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FYI, I just found this calculator site:

Maximum Span Calculator for Joists & Rafters

putting in 2x8 joists 16-in on center and a load capacity of 40 lb/sqft live load (furniture, people, what not) plus 20 lbf/sqft dead (flooring and such), it gives a max span of 13'7". 20 lbf/sqft dead load would be equivalent to laying down 1/2" thick steel tile, so whatever you're using is almost certainly lighter than that, and you'd almost definitely be safe without any of the reinforcement you added when you did the tile in the first place.
 
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Old 01-08-15, 06:23 PM
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I have an easy way to transfer the loads for all joists so the span will still be 8 feet or less -- except for one joist.
rmathome,

I may repeat myself, sorry.
You built a wall with header to support tile.
You say new bath will support the section you want to remove except for one joist, that's what I assume the above quote means. That one joist is going nowhere.
This is overkill at it's finest. We're not building a bridge here.
I don't want to go as far as to say stiffening wasn't required, but if it was, you have it well covered.
 
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Old 01-09-15, 05:33 AM
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That one joist is going nowhere
I kind of figured that when I started and it is only reinforced on this thread. The only reason I want to keep the reinforcement is because if I was wrong, and a tile cracked, there is nothing I can do about it.

I think I will joist choose the easiest of the methods. It shouldnt take more than 20 minutes to implement and even if it only adds marginal strength--it probably isnt needed anyway--but I will sleep well that first night.

Thanks so much for all of the input.
 
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Old 01-09-15, 06:14 AM
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Yeah, Sistering will probably be easiest. All your ideas are good and will work.
 
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Old 01-09-15, 07:39 AM
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I have looked for joist hangers but cannot find one that is oriented so that the crosspiece is supported and hangs a joist.

the best I could find is this:

http://images.lowes.com/product/conv...15301001lg.jpg

I think this will be easy enough also. A few cross pieces and then 4 of these hangers. On the inside of the joists and cross pieces. then a support under the cross pieces.

I think should be just fine.
 
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Old 01-09-15, 07:49 AM
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Name:  strongtie.jpg
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These are better. You should be able to find them at the hardware store.

The one you linked to is a hurricane tie.

When you do find these hangers, the store should have the special nails for them in the same section.

Uh, On second thought maybe it's not a good idea to bang on those joists with hammer. I would still use the hangers.
 

Last edited by Handyone; 01-09-15 at 08:12 AM.
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Old 01-09-15, 09:38 AM
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But that is a regular joist hanger. Its already labeled as W B H so I'll use those labels in my explanation.

This hanger would work if I wanted to hang a joist from the end of that joist, as they usually are hung. H would get nailed into a support beam and W would hold the end of the joist. The support beam has the strength so the joist can hang from it.

But I am not hanging a joist from the end, I am in the middle of the joist already.

So I would need to use this hanger such that H is nailed into the side of the joist and the crosspiece fits into W.

By doing this I am hanging the cross piece from the joist--even though the crosspiece is the one that is being supported with a stud underneath it.

I figure I needed something that will straddle the crosspiece, sort of like this:
Name:  hanger.jpg
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The hurricane tie I showed might not be strong enough. But thinking was that I can nail it into the face of a crosspiece (which has a stud under it) and then the metal tie bends at a 90 and it can be nailed to the side of the joist. Then the joist is truly hanging from the supported crosspiece.

I am assuming I am just misunderstanding something--I just dont know what.
 

Last edited by rmathome; 01-09-15 at 09:54 AM.
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Old 01-09-15, 09:53 AM
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Yeah,
It's hard to visualize without pictures. It sounds like you just want "blocking". For instance, between joists 16"o.c. you would have a 14-1/2" block.
If that's the case, just end nail or screw it into joists, or toenail.
You can always use your idea of sistering the joist with a short piece also, if that 1-1/2" of extra lumber will allow the bearing area you want. I think you can't go wrong either way.
 
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Old 01-09-15, 10:07 AM
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I dismissed end nailing or toeing because I didnt think it would add much strength.

Although, at this point, based on everyone's input, I think I have spent way much more time on this than it probably deserves.
 
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Old 01-09-15, 10:19 AM
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It won't add much strength as far as being attached to adjacent joists, but it will provide a little and that's what you were looking for. 2 Things:

1. At a minimum, the blocking will support at least 14-1/2" of floor area. Not ideal the way it carries the load, but there's really only a very small load if any.
2. Do not underestimate the strength of a nail or a structural screw.

Good luck on your project, you're doing good.
 
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Old 01-09-15, 06:45 PM
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I dismissed end nailing or toeing because I didnt think it would add much strength.
My grandmother's basement wall was bowing in and was failing from hydrostatic pressure. A foundation came in and used 4" metal I beams standing vertical against the wall to stop it from moving any further. The bottom of the I beam was put in a hole in the floor and concreted in. The top was held in place between the floor joists with bridging. The bridging is end nailed to hold it in place. The I beam is touching the block wall along it's entire length. That means it is bent and putting load on that bridging. Certainly not the way I would have done it, but it appears to be working.

My house was built in 1928. The floor joists do not sit on top of the center beam. They are toe nailed to it. There is a 1x2 ledger on the bottom of the beam with the joists notched, but be sure most of the weight is on those toenails. Nails are surprisingly strong. They hold many homes together. Toe nailing is far superior to end nailing and joist hangers are even better.
 
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Old 01-09-15, 10:50 PM
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Well, thank you all for so much input.
 
 

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