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Can I use a large LVL with 22-23 ft span to stiffen existing floor if only supported at ends?

unklegwar's picture

My house uses 2x8s for the first story flooring, and they span a wee bit too far for 2x8s at about 12' 8" or so.
The floor upstairs is bouncy. Not horrible, but enough.


Problem is, we'd like to, in the not to distant future, put engineered wood flooring and/or tile/stone down, and are concerned that the floor will just not take the weight as-is.
Further complicating is that the basement is split into 2 sections. 1 section is a 4' high crawlspace with poured floor. THAT section I figure I can put a stiffener beam down the middle of and put a jackpost every 5" if I have to, even on just the poured floor.
The other half is a full height (8' ish) poured floor area that I've converted to my woodshop. Since it's my woodshop, and it's net dimensions are about 12' 3" x 23 feet, I really don't want to slap a jackpost in the middle of it (it would be right where my tablesaw is) - it's already hard enough to maneuver large sheetgoods.

What I do have is some headroom to play with. The main HVAC trunk lines already run right down the middle and take about 12" off the headroom. I was thinking I can get an LVL in the range of 4" x 12" x 23' and run it next to the trunks, not lose any headroom, and this might be enough to take out the bounce without having to take the full weight like a normal beam. I can spare the space at the ends to support it with a jackpost or a couple of 2x4s nailed together.
One end would be up against a concrete wall, so the footings underneat that would come into play a bit, expecially if I nail the 2x4s TO the foundation wall. On the other end, I have a partition wall that divides the shop from the furnace/water heater area. I could beef up that wall with more 2x4s, and set the LVL into a pocket there.

I can't do sistered joists from below or above because of all the mechanicals and wiring and plumbing and spray insulation.

I might get 30% of them with plywood sistering with notches cut for wiring and such.

I did read about a bowstring truss technique, and also wonder if that would suffice here - if I have enough room for doing that, since those darn HVAC trunks are there.


Anyway, am I crazy thinking a beefy LVL could do the job with that kind of span?

By my quick calc, a single

By my quick calc, a single 2 x 12" deep LVL spanning 23' in length direction and supporting 6' of the floor above (15lb/ft dead load and 40 lb/ft live) will see ~8,000 psi.  Most LVLs will max out at 3,000 psi limit so ballpark you're looking at least 3- 2x LVL's or a metal beam.  For an arrangement such as this, however, I wouldn't trust a ballpark estimate (beyond rough planning).  (For example, in my ballpark calc, 3 x 2E LVLs didn't quite pass my jurisdiction's deflection requirement)


In my opinion, nothing wrong with the concept though, as long is it's properly braced and you spread the load from the 2x4s (depending on your slab).  Especially if you're just trying to do some supplemental load carrying.

To get an LVL to clear span

To get an LVL to clear span 23' it would have to be 18" deep or more.


If the headroom is a problem you might be able to cut a few inches out of the joists, put the beam up flush with the floor, and hang the joist halves off the beam.


Could you maybe put a 2x beam somewhere off center? If it was as little as 3' from the walls it would make a lot of difference on the stiffness of the floor.




Intead of a solid LVL, you

Intead of a solid LVL, you could also look at an open webbed truss that is 18" inches deep, then cut the floor joists and top hanf them from the top chord of the truss.  Lots of capacity, vary little weight.

YAY!  I love WYSISYG editing!  And Spellcheck!


As eneral rule of thumb, you

As a general rule of thumb, you can design one ply of a floor truss to carry roughly the same amount of weight as a single ply of an LVL.  But you need more depth than an LVL, so it really isn't much of a solution.

Get an Engineer

A decent structural engineer can run this out for you and give you the most cost effective solution. 

You are trying something different than the norm, so the building department will require an engineers blessing before they will give you a permit.