Sistering Floor Joists with LVL

[frankd]

I'm about to undertake a pretty large renovation project in my attached 2-car garage. We recently bought this house and unfortunately after buying, realized that the floor joists in the bedrooms (above the garage) were grossly undersized. The house was built in the 1950's and they used 2x10 floor joists running a span of about 21 feet. They appear to be about 12" on center but I haven't ripped the drywall off the ceiling yet. There is a noticeable sag in the floor that needs to be fixed.
My plan is to use several beams supported by jack posts and slowly (over the course of several weeks) push the floor up until it's pretty straight....and then sister each of them with LVL (1 3/4 x 9 1/2). My concern is that according to the span chart, the LVL should only be run about 19' if installed 12" on center...however they would be sistered to existing 2x10"s and I would add blocking between the joists to strengthen everything. I'm hoping that would help. My other concern is that the current floor joists are so deformed that I'm worried they will act against the the LVL rather than helping to support the floor since the joists have probably been bent for the last 30+ years

Has anyone else undertaken a job like this? I was thinking of calling in an engineer but they want over $600 and for that kind of money I'd rather just buy a few extra joists and double them up every 3-4 feet.

 

[Musicinabottle]

What sort of ceiling height in the garage? I ask because it would be stronger to run a large glue lam under the joists mid span. You could even temporary support the joists to either side of the glue lam location, then cut out a space in the joists for the beam and let it in, and hanger the joists. This of course assuming that you have two garage door openings and not one?

 

[GMCGarage]

Unfortunately the lvl is controlled by deflection, abut 1.3" at max load. a 11.25" deep one would get you down to about 3/4" inch, very much in the range you want to be in. the shear is low enough you could notch at the ends to install.

If you can sister 2x10 to 2x10, the combined section gets you your deflection range too.

Installation is another issue. how are you going to get the beams in bearing at both ends? do you have room to slide into one side and then bring back?

For the amount of money you might save with a beam, pay the engineer to do his thing, and be happy.

When you go to sell, unless you hide your fix, the new buyer will want an engineer to sign off on it. Either way, you need to disclose it when you goto sell.

 

[Shiftless]

It’s hard to believe that 2x10s spanning 21 feet was EVER approved.
Is there any evidence of a previous middle support that was removed some time in the last 60 years? If some guy took out a big beam and a center post because it was “in his way”, that might explain your situation.
My garage was built in the 1950’s as well. 20 feet across with 2x10s but there is a steel I beam in the center so the span of the ceiling joists is only 10 feet.

 

[frankd]

Musicinabottle- The garage ceiling height is only about 7' ...maybe 7' 6". The joists run across the garage, parallel to the garage door. The easiest option is to just put a beam under the joists in the center of the garage but that would require a support column at each end...meaning one wound be directly in the center of the garage when I open the door. I would have the same issue with a concealed header.
So I REALLY want to go with sistering the joists and I don't wand do reduce the ceiling height which is why I want to stick with 1 3/4 x 9 1/2 LVL.


GMCGarage- Thanks for the additional info. As far as getting the LVL to fit in the pocket between the joists... I was thinking of using one of 2 approaches: The LVL that I've seen is pretty flexible so I think that a 21' piece on its side would have enough flex that I could cut it 1" short, slide one end in, bend it, and get the other end in. Once they're all in there, I would put up a temporary beam and slowly start jacking up the old joists at their lowest point until they were relatively straight....Then turn the LVL upright and get them in place. I know that I'd need to shorten the height of them at the ends by a 1/4"- 1/2" or so to allow them to be twisted upright inside of the cavity between the joists.
I called a few engineers and they all said that it would be $600+...which pisses me off in principle alone since it would at most amount to 20 min of work.

 

[frankd]

It’s hard to believe that 2x10s spanning 21 feet was EVER approved.
Is there any evidence of a previous middle support that was removed some time in the last 60 years? If some guy took out a big beam and a center post because it was “in his way”, that might explain your situation.
My garage was built in the 1950’s as well. 20 feet across with 2x10s but there is a steel I beam in the center so the span of the ceiling joists is only 10 feet.

I'm also surprised. The same builder built almost all of the houses in my community in the 1950's....and all of the houses have the same problem to some degree. There was never a center beam. None of the other homes in the area have center beams either. I checked with some of the neighbors and they all had the same sag issues but at some point I guess it stabilized. My house seems much worse than others in the area but the guy that I bought it from collected cars and the attic (above the bedroom) was PACKED with boxes of car parts so I'm sure that made the issue much worse.

It's not just the garage. The floor below the master bedroom (above the den) is 2 x 6 running just over 12' and they are sagging severely as well. I actually didn't notice the garage ceiling when we bought the house. I only noticed in in the bedroom and underbid because I knew it would scare other buyers off. Long story short..it didn't.

 

[Dirtydan69]

I once bought a house that had full 2x6 floor joists spanning anywhere from 14-16 feet. The floor would bounce and flex when walking on it. House was built in the 1890’s originally on a crawl space. In later years indoor plumbing came in and they dug a basement. I sistered, with glue and screws, ripped down 3/4” plywood to both sides of the joists. Seams were staggered. After jacking and supporting said joists. Fixed the problem but yours seems way more extensive. I would seriously consider paying an engineer.

 

[sz0k30]

The CHEAP way out many times happens to be the bad way out.

 

[Ben W]

Something to think about on the practical side -
Has it been this way for the last 30 years? By what you're saying - yes.
Has the floor collapsed yet in the current configuration? No.
By you adding the LVLs are you going to make it worse? Not likely.
So your plan is only moving in the right direction even if it might not meet all code requirements or align with a product sheet.

I think you'll have a tough time getting the LVLs to rotate if you leave them full height at the ends. Suggest coping out an inch and shimming them up once in place.

An engineer is taking on liability to design or check something. For his (or her) perspective, it may not be worth his time (liability) for say $50.

If this situation didn't come up in your recent house purchase, then it would be unlikely to when you were to sell it in the future.

 

[Shiftless]

Wow!
All the houses the developer built have sagging floors from using undersized joists and excessively large spans.
I guess the go-go times of the 1950’s allowed builders to get away with stuff like that and municipalities just looked the other way regarding code enforcement.
I hope you and your neighbors don’t have the original Federal Pacific electrical panels and stab-lok breakers.

 

[cwise]

I agree with Ben, I had a house with engineered trusses in the floor. Floor joists were 14" high, 19 ft span on 18inch centers on the first floor, I did just what you are proposing here. I jacked up the middle of the existing floor using steel jack posts and 4x4's, I put full height glue lam beams in to sister the exiting truss joists. I nailed them to the original with 12 penny nails staggered on top an bottom about every foot over the span. I installed the glu lams by sliding them in laying flat and stood them up. Standing the glu-lams up from flat to next to the joists was much easier than I expected, stand the top up a bit an hammer. The one advantage I had was that since this was in the basement there was a beam in the middle, so I had plenty of room on the ends to slide the glu-lams in. The sag in my floor was only about an inch and half in the middle, I got it all out and the floor was solid as concrete when I was done. I sold the house and no one involved in the entire process, no realtor, home inspector, buyer, township inspector, no one, mentioned anything about this even though you could clearly see the sistered joists in the unfinished basement.

 

[Budman01]

Have your LVL source provide engineering calculations for your situation, and sell you appropriate LVLs. You could use 11-1/2 with hangers on each bearing point, again with appropriate load calcs

 

[strutaeng]

Just provide a adequate beam to convert the single span to a 2-span. Maybe push the beam up to some specified force to remove some of the dead load off the 2x10s, but I don' think you can't bring them back to level considering long-term creep effects of wood. Neither will it be necessary to sister 2x10 for a shorter span if they are at 12" o.c. unless you have some heavy flooring.

I would hire an engineer to run the numbers and you can do the repairs. He'll design the beam and the supporting columns, along with checking the footing and will provide sealed design drawings. You can talk to him directly and discuss options framing schemes. Essentially, he'll take out the "guesswork."

Good Luck.

 

[Lelandwelds]

Something to think about on the practical side -
Has it been this way for the last 30 years? By what you're saying - yes.
Has the floor collapsed yet in the current configuration? No.
By you adding the LVLs are you going to make it worse? Not likely.
So your plan is only moving in the right direction even if it might not meet all code requirements or align with a product sheet.


If this situation didn't come up in your recent house purchase, then it would be unlikely to when you were to sell it in the future.

The realtor will be looking at the curb appeal, location, and any features he can bullet point.
The buyer is staring at the kitchen and bathroom.

If they notice the garage, it will be to wonder if their SUV with the never tested offroad capability will fit.

 

[frankd]

Something to think about on the practical side -
Has it been this way for the last 30 years? By what you're saying - yes.
Has the floor collapsed yet in the current configuration? No.
By you adding the LVLs are you going to make it worse? Not likely.
So your plan is only moving in the right direction even if it might not meet all code requirements or align with a product sheet.

I think you'll have a tough time getting the LVLs to rotate if you leave them full height at the ends. Suggest coping out an inch and shimming them up once in place.

An engineer is taking on liability to design or check something. For his (or her) perspective, it may not be worth his time (liability) for say $50.

If this situation didn't come up in your recent house purchase, then it would be unlikely to when you were to sell it in the future.

Thanks Ben,
This is exactly what I was thinking. The house was built in 1955 and has been this way for over 60 years. If anything, I feel like the town should be paying for this since they were the ones that approved the construction in the first place...but of course that's not going to happen.
I was thinking of leaving it as-is but we've been in the house for a year and it's driving me nuts. I agree that I wont be able to rotate the LVL once it's between the joists if I leave it at full height. The LVL comes in 24ft lengths and I only need about 21ft so I was going to take a scrap piece off the end and find out how much I would need to shave off the end in order to allow it to rotate.
The other option is to get the LVL in place between the walls, cut the top plate, and bring the LVL straight up...and then support it with a 4x4 on each side. I'm thinking of doing this every 3-4 feet or so and then just sister all of the other joists. Looking at the span chart, if I install the LVL 12" on center they can be run 20' 10"... so I'd only be extending that by 2-3"...but I'm also going to sister them against the existing joist, double them up every few feet...and add blocking. In my mind I think it's overkill.

I did put a call in to a few other local engineers to see what they'd charge.

 

[GMCGarage]

The realtor will be looking at the curb appeal, location, and any features he can bullet point.
The buyer is staring at the kitchen and bathroom.

If they notice the garage, it will be to wonder if their SUV with the never tested offroad capability will fit.

Correct, the home inspector will pick up on the other stuff.

 

[GMCGarage]

Musicinabottle- The garage ceiling height is only about 7' ...maybe 7' 6". The joists run across the garage, parallel to the garage door. The easiest option is to just put a beam under the joists in the center of the garage but that would require a support column at each end...meaning one wound be directly in the center of the garage when I open the door. I would have the same issue with a concealed header.
So I REALLY want to go with sistering the joists and I don't wand do reduce the ceiling height which is why I want to stick with 1 3/4 x 9 1/2 LVL.


GMCGarage- Thanks for the additional info. As far as getting the LVL to fit in the pocket between the joists... I was thinking of using one of 2 approaches: The LVL that I've seen is pretty flexible so I think that a 21' piece on its side would have enough flex that I could cut it 1" short, slide one end in, bend it, and get the other end in. Once they're all in there, I would put up a temporary beam and slowly start jacking up the old joists at their lowest point until they were relatively straight....Then turn the LVL upright and get them in place. I know that I'd need to shorten the height of them at the ends by a 1/4"- 1/2" or so to allow them to be twisted upright inside of the cavity between the joists.
I called a few engineers and they all said that it would be $600+...which pisses me off in principle alone since it would at most amount to 20 min of work.

Unfortunately the location you are in the price is high. I would be half that to do the engineering, thats with a site visit too!

 

[Hpozzuoli]

You can probably get away with sistering 2x10’s for the entire span. I would also use a post or two. Without being able to get steel or lvls in there I think your problem will return without the posts. The posts will also make this a quick, long term solution. Obviously all per engineer including post location and size.

 

[Radix2]

To cut the span down, you don't have to run your new beam under and lose headroom.

Put in a flush beam

You will need to add (likely) a new header over the garage door to now carry some of the floor load. Build temp supports under the center of the floor. Cut your current floor joists in half and open space for your new beam. Add joist hangers to new beam, raise into place and level your floor (easy now since the warp of the joists is cut ). Attach to header, add post under inside end of beam.

No need for more joists, simpler to execute.

Now, we need to see if a lvl stack at x10 can carry the center beam load, and same for header if garage door. Could also do instead steel for these two to fit the space.

If you are engineering savvy you can download forte for free to calculate the beam specs. Is the bedroom floor above the same dimensions as the garage ceiling?

 

[frankd]

I agree with Ben, I had a house with engineered trusses in the floor. Floor joists were 14" high, 19 ft span on 18inch centers on the first floor, I did just what you are proposing here. I jacked up the middle of the existing floor using steel jack posts and 4x4's, I put full height glue lam beams in to sister the exiting truss joists. I nailed them to the original with 12 penny nails staggered on top an bottom about every foot over the span. I installed the glu lams by sliding them in laying flat and stood them up. Standing the glu-lams up from flat to next to the joists was much easier than I expected, stand the top up a bit an hammer. The one advantage I had was that since this was in the basement there was a beam in the middle, so I had plenty of room on the ends to slide the glu-lams in. The sag in my floor was only about an inch and half in the middle, I got it all out and the floor was solid as concrete when I was done. I sold the house and no one involved in the entire process, no realtor, home inspector, buyer, township inspector, no one, mentioned anything about this even though you could clearly see the sistered joists in the unfinished basement.

Since you've been through this I have a question... After you completed your project, did you notice any nails/screws popping out of the floor above the ceiling? Currently, the floor above the garage is very noisy/squeaky when you walk on it. I'm worried that it's going to get tremendously worse but also worried that some nails/screws are going to pop up. The bedrooms above the garage are carpeted so once the project is complete, I was going to try and pull back the carpet and drive some screws through the floor into the new joists to tighten everything up.

Thanks everyone for all the replies. I called a local lumber supply dealer and luckily got one of the old timers that works there. He told me that sistering every joist was probably overkill but I plan on doing it anyway. Nothing wrong with overkill. He also gave me a great price on the lumber at $90 a piece.

 

[Ben W]

Nails or screws don't want to pop without a reason. Nails popping (and squeaks) are likely due to movement. If you make the whole assembly more rigid than it is now, then it would make the nails or screws to be less likely to pop. I don't think you need to worry about them.

Btw, there are screw products you can use to screw down the flooring right through the carpet. They snap off once you hit the right depth. No personal experience with them, but saw it on This Old House so it must be legit.

 

[theoldwizard1]

If you can sister 2x10 to 2x10, the combined section gets you your deflection range too.

True !

Installation is another issue. how are you going to get the beams in bearing at both ends? do you have room to slide into one side and then bring back?

That was my first thought !

When you go to sell, unless you hide your fix, the new buyer will want an engineer to sign off on it. Either way, you need to disclose it when you goto sell.

Good point !

 

[TomC750]

Unfortunately the location you are in the price is high. I would be half that to do the engineering, thats with a site visit too!

I would forget the engineer. You run the risk of having the engineer provide a over the top solution that spends a lot of your money in addition to the $600.

I was involved in a bridge building project for a non profit. The span was only 80'. However, because grant money was involved, we had to have a licensed
engineer. I was not impressed with the design, so I changed it, using the same materials. I got the engineer to OK it. It worked out well. I was only an excavation equipment operator. Sometimes practical experience trumps a sheepskin. Therefore I would review the above solutions, pick the one you like best and go for it. Good luck.

 

[73fxe]

I think Radix2's idea is the best. Just lift the floor to flat, build a temp. wall on both sides of center and cut in a beam.

 

[GMCGarage]

I would forget the engineer. You run the risk of having the engineer provide a over the top solution that spends a lot of your money in addition to the $600.

I was involved in a bridge building project for a non profit. The span was only 80'. However, because grant money was involved, we had to have a licensed
engineer. I was not impressed with the design, so I changed it, using the same materials. I got the engineer to OK it. It worked out well. I was only an excavation equipment operator. Sometimes practical experience trumps a sheepskin. Therefore I would review the above solutions, pick the one you like best and go for it. Good luck.

Sounds like you got lucky.

 

[GMCGarage]

I think Radix2's idea is the best. Just lift the floor to flat, build a temp. wall on both sides of center and cut in a beam.

And reinforce the header over the garage door, and then the other end of the beam and what its bearing on too. Simple.

 

[TractorJeff]

I'm surprised the Door Header isn't sagging already!

 

[Ironcrow]

Sounds like you got lucky.

The engineer checked the redesign. So the luck wasn't that the bridge stayed up, it was that the amateur redesign was sound?

On the other hand it was an engineer who came up with the OP's original springy floor so everything is not necessarily improved by an engineer's stamp?

 

[Shiftless]

On the other hand it was an engineer who came up with the OP's original springy floor so everything is not necessarily improved by an engineer's stamp?

I bet the original design did NOT include 2x10s spanning over 20 feet. My money would be that the original drawings included a center beam and maybe even a center post which the builder decided to omit to save a few bucks and to make the garage clear span and therefore more saleable. Buyers don’t like steel poles right in the middle of a 2 car garage.

 

[GMCGarage]

The engineer checked the redesign. So the luck wasn't that the bridge stayed up, it was that the amateur redesign was sound?

On the other hand it was an engineer who came up with the OP's original springy floor so everything is not necessarily improved by an engineer's stamp?

Well

 

[frankd]

I think Radix2's idea is the best. Just lift the floor to flat, build a temp. wall on both sides of center and cut in a beam.

This was my first thought but Its not really feasible. The current joists run parallel to the garage door. So I would have to run a header from above the center of the garage door to the center of the back of the garage. The back of the garage is easy...but the current garage door is 16' wide and already has a steel header over it because the wall above the door is supporting the roof. There is no sag at all in the steel header above the garage but considering how $hitty the house was built, I don't want to put any more weight on it...so I would need to install another header right behind it to take the load of the sagging floor. ...which means that I would into clearance issues with my jackshaft garage door opener as well as the torsion spring setup above the door.

And reinforce the header over the garage door, and then the other end of the beam and what its bearing on too. Simple.

I was hoping I could do something like this but I don't think it'll work, as per my comment above.

I'm surprised the Door Header isn't sagging already!

So am I. I feel like this house is turning into the money pit. The wall above the garage door is a steel I-beam but it is not supporting the floors, just the wall above it, which is supporting the weight of the roof.

The lumberyard that I'm working with checked the span charts and the LVL that I will be using can span 20' as a floor joist when installed 12" on center (40psf live load, 12psf dead load. max deflection L/360). My span is about 21' but the joists will be sistered to existing 2x10's...and I'm also going to double up the LVL in 2 spots where the sag is the most severe.

I'm going to start tearing down the drywall and insulation next week. Hopefully I won't have to re-route too much wiring in the process.

 

[RCornell]

http://www.awc.org/codes-standards/calculators-software/spancalc


Is a good source. Live load and dead load are key. At 12" on center, 19'1" is acceptable for a 2x10. Sagging says that dead load probably exceeds 15psf.

 

[GMCGarage]

Just remember that your existing 2x10 has capacity. Putting a new LVL up there to take all the load might not be necessary. Not to beat the dead horse, but at 90$ a piece, x 15-20 of them, you might invest in the engineer and see if you can reinforce with 2x10's @ 30$ a piece. If shear is not an issue, you might not need the whole length reinforced either, just maybe the middle 2/3'ds to stiffen the existing joists once jacked into place.

Just a thought.

 

[Radix2]

This was my first thought but Its not really feasible. The current joists run parallel to the garage door. So I would have to run a header from above the center of the garage door to the center of the back of the garage. The back of the garage is easy...but the current garage door is 16' wide and already has a steel header over it because the wall above the door is supporting the roof. There is no sag at all in the steel header above the garage but considering how $hitty the house was built, I don't want to put any more weight on it...so I would need to install another header right behind it to take the load of the sagging floor. ...which means that I would into clearance issues with my jackshaft garage door opener as well as the torsion spring setup above the door.


I was hoping I could do something like this but I don't think it'll work, as per my comment above.


So am I. I feel like this house is turning into the money pit. The wall above the garage door is a steel I-beam but it is not supporting the floors, just the wall above it, which is supporting the weight of the roof.

The lumberyard that I'm working with checked the span charts and the LVL that I will be using can span 20' as a floor joist when installed 12" on center (40psf live load, 12psf dead load. max deflection L/360). My span is about 21' but the joists will be sistered to existing 2x10's...and I'm also going to double up the LVL in 2 spots where the sag is the most severe.

I'm going to start tearing down the drywall and insulation next week. Hopefully I won't have to re-route too much wiring in the process.

Are you sure there will be a clearance issue to add the extra header ? Remember that you are adding a flush beam, the header can be flush too - when you open the ceiling you will have an entire open bay along the current garage header available to place the header inside.

Just a thought and you may be right, but realize that the new flush beam can be hung from the new "header" by joist hangers as well.

The size may not be all that big since you just have a simple floor load on it., no roof, no wall, etc.

depending on your set up, you could even put the new header back a bay or two and support it on the sides with posts at the walls. but still above the ceiling and in no way interfering with the garage door, etc.

The trick is to get the span in your height.

 

[bczygan]

I'm about to undertake a pretty large renovation project in my attached 2-car garage. We recently bought this house and unfortunately after buying, realized that the floor joists in the bedrooms (above the garage) were grossly undersized. The house was built in the 1950's and they used 2x10 floor joists running a span of about 21 feet. They appear to be about 12" on center but I haven't ripped the drywall off the ceiling yet. There is a noticeable sag in the floor that needs to be fixed.
My plan is to use several beams supported by jack posts and slowly (over the course of several weeks) push the floor up until it's pretty straight....and then sister each of them with LVL (1 3/4 x 9 1/2). My concern is that according to the span chart, the LVL should only be run about 19' if installed 12" on center...however they would be sistered to existing 2x10"s and I would add blocking between the joists to strengthen everything. I'm hoping that would help. My other concern is that the current floor joists are so deformed that I'm worried they will act against the the LVL rather than helping to support the floor since the joists have probably been bent for the last 30+ years

Has anyone else undertaken a job like this? I was thinking of calling in an engineer but they want over $600 and for that kind of money I'd rather just buy a few extra joists and double them up every 3-4 feet.

Not knowing the exact loads and spans in both directions, you could us higher strength or deeper LVL's or cut the span of the joists by installing a steel or wood (LVL) beam at mid-span of the joists. Cut the beam in to the joists to avoid dropping below ceiling level.

Bill

 

[GMCGarage]

Are you sure there will be a clearance issue to add the extra header ? Remember that you are adding a flush beam, the header can be flush too - when you open the ceiling you will have an entire open bay along the current garage header available to place the header inside.

Just a thought and you may be right, but realize that the new flush beam can be hung from the new "header" by joist hangers as well.

The size may not be all that big since you just have a simple floor load on it., no roof, no wall, etc.

depending on your set up, you could even put the new header back a bay or two and support it on the sides with posts at the walls. but still above the ceiling and in no way interfering with the garage door, etc.

The trick is to get the span in your height.

Based on a quick calc, the header would need to be 3.5x16 LVL. You also now have about 2.6K of load at each end to deal with, down to slab, footing, etc???.

Plus the beam running perpendicular.

Still might be cheaper.

 

[Radix2]

Based on a quick calc, the header would need to be 3.5x16 LVL. You also now have about 2.6K of load at each end to deal with, down to slab, footing, etc???.

Plus the beam running perpendicular.

Still might be cheaper.

I fired up Forte to look at the center beam too. Not too practical in the x10 depth either. The beefed up joists are probably the best way. A beam solution would need some steel to fit in the depth.

 

[engineer2]

Can you open up the end of one wall to the exterior to slide the beam in? Did this for a project on my house. Pulled the siding off, opened up the wall, slid the LVL in, closed up the hole. Took all of 30 minutes.

Be aware LVL comes in a couple of different strengths. Look up the brand, color code, and the marking on the beam. L/360 calculators are on the internet.

You might also consider a steel I-beam floor support.

 

[ishiboo]

I've leveled a lot of floors... and one thing I've found is that you're often better off removing what's currently there.

As you mentioned, the joists having sagged makes them pre-loaded in the direction you don't want to be. Jack them up, install your new floor joists level which are rated for the span, remove the jacks and all that pre-load actually bows your NEW floor. So you need to over-size the joists to counteract that versus what the span tables indicate.

Not only that, but the bow if you cut it in the center to install a beam remains, and causes the floor to take a "W" shape if you jack the center, because they are curved on their length.

Just my .02...

 

[TommyK]

I've leveled a lot of floors... and one thing I've found is that you're often better off removing what's currently there.

As you mentioned, the joists having sagged makes them pre-loaded in the direction you don't want to be. Jack them up, install your new floor joists level which are rated for the span, remove the jacks and all that pre-load actually bows your NEW floor. So you need to over-size the joists to counteract that versus what the span tables indicate.

Not only that, but the bow if you cut it in the center to install a beam remains, and causes the floor to take a "W" shape if you jack the center, because they are curved on their length.

Just my .02...

^^This^^

You will not get 2x10's on that span that have sagged over the course of 60+ years straight by jacking in the center. You will get some of it out but you won't get all of it. As a result you will have a hell of a time getting 10" LVL's in place without some cutting. If you really want it right you will have to room the floor above before sistering.