NA. Supplemental beam to eliminate living room bouncy floor size?

Huckster79

Huckster79

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Huckster79
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I live in an older home, prob 20s/30s, honestly much of it wasn’t built well to begin with. We are in the midst of a pretty deep dive remodel. We have done all ourselves minus siding and a furnace and duct replacement.

The living room floor is over “clean crawl space” the floor is bouncy, not squeeky, but has that old house “China cabinet rattle.”

the joist are 2x8, not modern dimensional lumber not quite true 2x4… spanning 11 ft, and spaced 18-21” apart… it’s about 20ft long.

I’m thinking of running a supplemental beam to split the span, considered sistering them but that would be rather difficult to sister all full span. I’m not planning to lift any unevenness-just a slight push up in the center to make the floor have a more solid feel.

I’m thinking a doubled 2x8 down the middle? Held by 3 house jacks or should I do 4?
 
My great grandfather was famous for saying that if 1 2x4 would do, use 2. The house my parents bought in Pullman, and lived in for over 30 years, was built that way. Use 4 jacks.
 
If it’s not already there consider cross blocking instead. Cut short pieces and put them between each joist connecting one joist to another. You will be surprised at how much that stiffens it up as it transfers the point load on one joist to all the rest.
 
Even if you can't sister them full span, if you can do it partially (say 8' in the middle of the 11' span), it'll make a big improvement as most of the flex is in the center of the beams. But a big beam crosswise under them supported to the ground would help even more, as long as the ground it's supported by is stable.
 
Huckster79 said:
I live in an older home, prob 20s/30s, honestly much of it wasn’t built well to begin with. We are in the midst of a pretty deep dive remodel. We have done all ourselves minus siding and a furnace and duct replacement.

The living room floor is over “clean crawl space” the floor is bouncy, not squeeky, but has that old house “China cabinet rattle.”

the joist are 2x8, not modern dimensional lumber not quite true 2x4… spanning 11 ft, and spaced 18-21” apart… it’s about 20ft long.

I’m thinking of running a supplemental beam to split the span, considered sistering them but that would be rather difficult to sister all full span. I’m not planning to lift any unevenness-just a slight push up in the center to make the floor have a more solid feel.

I’m thinking a doubled 2x8 down the middle? Held by 3 house jacks or should I do 4?
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If it's not really sagging much and you just need to get rid of a little bounce and rattle just one support midway should be more than a enough. What's the soil like down there. Give the jack some kind of footing. Probably don't need much as you can go under and crank it up from time to time until things have settled in. I'm guessing that seeing as how it's old rough cut lumber, there may be some variance in size. And some may have a little more crown than others. Get some builders shims or just shingles and tap and glue into any gaps. Don't over due it. A wedge driven in can have more lifting force than you think. I learned this the hard way. The cracks in the plaster didn't look to bad after a little patch work:frown2:. Secure each joist solidly to the beam. Simple joist hangers will work fine. After putting them on is when you fill any gap with shims. What you have now is what's known as a strong back except it's under the joists rather than over. Google it. The result is, any downward pressure over a joist will have to move the adjacent joists with it to deflect. By sistering the beams, I assume you mean butting two end to end. What @Dana said above about just doing it partially will work just fine. Do the nailing about an inch in from the edges. Nailing in the middle doesn't help much. They just kinda act like pivots. It's the ones along the bottom that actually do most of the work.
 
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Nuke it from orbit, it's the only way to be sure.

(I should be outside the blast radius and fallout zone)
 
Thank you all!

The ground in the crawl is sand… so I’m thinking a cement pad under each jack. I think I’ll go the 4- they aren’t pricey.

I guess my other concern w sistering vs a beam is I sistered 3 under the kitchen as that will be a basement bedroom (house is half basement half crawl) so a beam wasn’t an option. The sistering didn’t help much nor did cross blocking I put there… which really put me in a fowl mood after working most of a Sunday on it! :)

so on that area I’m going to try glue and screwing a 2x4 flat on the bottom to make them half of an “I” beam shape. Reading some folks have used that to great success.
 
Huckster79 said:
Thank you all!

The ground in the crawl is sand… so I’m thinking a cement pad under each jack. I think I’ll go the 4- they aren’t pricey.

I guess my other concern w sistering vs a beam is I sistered 3 under the kitchen as that will be a basement bedroom (house is half basement half crawl) so a beam wasn’t an option. The sistering didn’t help much nor did cross blocking I put there… which really put me in a fowl mood after working most of a Sunday on it! :)

so on that area I’m going to try glue and screwing a 2x4 flat on the bottom to make them half of an “I” beam shape. Reading some folks have used that to great success.
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If it's sand, and you're going to be relying on that, don't be shy with the size of the footing. And I would definitely use jacks like you said instead of a fixed pier. That sand gonna move. I'm having trouble getting my head wrapped around the 2X4's on their side idea. Yeah, that will add an inch and a half to the size of the joists. A lot of joists. Doing a strong back will save you time and money and will be more effective. But maybe that inch and a half will be all you need. Just how did you do that sistering? Are you talking about attaching a piece of lumber along side each joist? Or using two pieces of lumber side by side to 'build a beam' in place? It sounded like that's what you meant in your OP. But now it sounds like each joist by what you described under the kitchen.
 
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Yea the flat 2x4 is supposed to help the tension force I believe, on another forum an engineer described it- tgat mathematically it almost doubled the strength of a 2x8 by helping to eliminate it “twisting” under weight and the tension force - he explained it better than I and admitted in real world scenario it likely doesn’t fully double its strength as the mathematical formula he used was as if it was one piece of wood in that shape… I figure for a few sticks it’s worth a shot. Especially after sistering 3 of them and solid blocking them all.

When sistering them I was able to do one full lenght and two others most of the way - I put a new 2x 8 next to the old, jacked the middle of the old joist a “skoch” constuction adhesived and screwed them together.
 
Huckster79 said:
Yea the flat 2x4 is supposed to help the tension force I believe, on another forum an engineer described it- tgat mathematically it almost doubled the strength of a 2x8 by helping to eliminate it “twisting” under weight and the tension force - he explained it better than I and admitted in real world scenario it likely doesn’t fully double its strength as the mathematical formula he used was as if it was one piece of wood in that shape… I figure for a few sticks it’s worth a shot. Especially after sistering 3 of them and solid blocking them all.

When sistering them I was able to do one full lenght and two others most of the way - I put a new 2x 8 next to the old, jacked the middle of the old joist a “skoch” constuction adhesived and screwed them together.
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Yeah. It will help some with the tension along the bottom. When it gets force from above it wants to put the top in compression and the bottom in tension. That's about what I was describing above with nailing along the edges and the bottom is what does most of the work. The twisting is a thing although you said you have blocked between the joists so that issue is already taken care of. That is the reason for blocking. Sometimes it's done this way. Accomplishes the same thing.

images
 
You aren’t bearing a load, just limiting deflection. That won’t take much structurally to accomplish. In any case I’d use VersaLam instead of dimensional lumber. If your 2x8 bows if won’t serve its purpose.
 
The rental house I lived in when I was in Tennessee had a similar floor and it sat on a central beam supported by those crappy concrete pier blocks. There were the same pier blocks around the perimeter of the house and nothing else holding the structure above the ground.

The floor was so bad that if someone jumped up and down in the kitchen, it would knock you off the toilet in the master bedroom!

Every home I have owned has a pre-stressed concrete slab foundation so that I don't have to put up with wobbly floors...
 
After you described the "sistering" you did in the kitchen, I understand your approach. The 2X4 flat along the bottom probably would have helped a lot more. The additional support beam you want to use in the living room should work okay since it will cut the span in half and reduce the deflection considerably. I did that for our old house and it helped a LOT.
 
When we remodeled our kitchen and added a peninsula concrete counter tops over the center of the floor joist span (for those keeping track, concrete is heavy), the contractor suggested sistering in floor joists, which are about as long as what you're talking about. However we have a full finished basement not a crawlspace, so there was more area to work with. I can tell you that the sistered joists work well and we have no bouncy effect or feel, so I think it was worth it.

Really, anything that provides the center of the joists some extra support should do. Without pictures it's hard to say much beyond that, but anything you do should be better than what you have.
 
This sistering thing is sexist. Need a new word. I'll start. Joist jointing. nah, joint will get misconstrued.
 
Update! The 2x4 glued and screwed flat-ways across the bottom did it! Stuff will jiggle a bit if I jump in the kitchen but doesn’t rattle even when I walk really heavy acccross the kitchen now!

now into the next adventure: finishing basement rooms and gutting kitchen! Going to do some “faux cement” walls and counter - should be interesting!
 
Huckster79 said:
Update! The 2x4 glued and screwed flat-ways across the bottom did it! Stuff will jiggle a bit if I jump in the kitchen but doesn’t rattle even when I walk really heavy acccross the kitchen now!

now into the next adventure: finishing basement rooms and gutting kitchen! Going to do some “faux cement” walls and counter - should be interesting!
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By 'across' the bottom I assume you meant one perpendicular to and crossing all the joists as a strong back. Or did you do it to each joist along the bottom turning each of them into kinda an I-beam?
 
luvflyin said:
By 'across' the bottom I assume you meant one perpendicular to and crossing all the joists as a strong back. Or did you do it to each joist along the bottom turning each of them into kinda an I-beam?
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kind of like an I-beam style.
 
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