Joist Span Table for 2" by 6" LVL joist

[DIYBuilder]

I need the span table for Boise Cascade VERSA-LAM 2.0-3100 LVL 2x6 (nominal) floor joists, for a 12 foot span under a residential living area with dead load = 20psf and live load = 40psf.
This is not listed in the IRC 2018, nor does the Boise website list for 2x6 LVL.

Does anyone know?
Thanks

 

[DIYBuilder]

The IRC 2018 table R502.3.1(2) shows for Douglas fir-larch (the strongest lumber listed), a 2"x6" with 12" spacing can span 11' 4" (!) for dead load = 20psf and live load = 40psf. SO I assume that Boise Cascade VERSA-LAM 2.0-3100 LVL can do better? Is it true?

The reason I want to know thei is because I want to replace the basement ceiling (=kitchen floor) joists, which are 2x8 at 16", with 2x6 LVL joists at 12" so that my basement height will be 7' from finished floor to finished ceiling (after I finish it). Or rather than replace the existing joists, I will just sister each of the 2x6 joists to the existing 2x8 joists and trim off the bottom 2 inches of the 2x8's, thus getting at least as good as 2x6 joists at 12"
According to the IRC 2018, I can even use 2x6 Douglas fir-larch for this, but I was wondering if the LVL's will be even better (stronger and with less bounce). Hence I need a table.

Any advice on whether my plan to gain some height in the basement is a bad idea would be greatly appreciated!

 

[jar546]

Does anyone know?

They are engineered products that need an engineer to spec out. They are designed as headers and beams, not joists which may explain why you can't find a span table.

 

[e hilton]

, I will just sister each of the 2x6 joists to the existing 2x8 joists and trim off the bottom 2 inches of the 2x8's, thus getting at least as good as 2x6 joists at 12"

How do you figure that? Sistering to 16” oc gives you 14” oc.

 

[mtlogcabin]

They have a software program that you can try for free. As Jar stated you may be using them for something they are not designed for so the software program may not help you.

Design and Operations Management

www.bc.com

 

[DIYBuilder]

Regarding the question by e hilton: If I sister all the joists that are 16" oc, the new double joists will all still be 16" oc. But now there is a total of 4 joists over a 16" span (really over say 18" now because the sistered joist adds 2" (really just 1.5")). I assume that is stronger than 1 joist at 12"oc.

Now, according the the joist table, I only need one 2x6 (nominal) at 12"oc if I use Douglas fir-larch. But it is easier to double all the joists at 16"oc than to replace them all with 1 joist at 12"oc.

Regarding comments by Jar546 and mtlogcabin, I need to check if a 2x6 LVL is better than a 2x6 Douglas fir-larch. If so I will go with 2x6 LVL.
Any flaws in my logic?

Also, I better check with the town inspectors first before I start hacking my joists!

 

[e hilton]

Flaws? Possibly. Don’t confuse the strength of the floor with the deflection. You probably don’t want the floor to bounce when you walk across it, like Aunt Marthas old house.

 

[DIYBuilder]

Thanks, so I should find out if 2x6 Boise Cascade VERSA-LAM LVL is both 1) stronger and 2) has less bounce, than 2x6 Douglas fir-larch.
That is the info I am looking for...

 

[wwhitney]

Does anyone know?

If you hack up your 2x8s, it's difficult to assign design values to them, as they will no longer be graded. For example, if you start with a particular grade which might allow knots of a certain large size as long as they are at least 2" from the edge of the member, and you remove 2" from the bottom of the member, now you may have a large knot right at the bottom edge of the member. In which case you no longer have that grade. So you should just consider your hacked up 2x8s to be oversized nailers and install new members that will be sufficient for the load and span on their own.

With a bit of reasonable extrapolation, you can do this via the span tables. Start with 2018 IRC table R802.4.1(2), which is a span table (for rafters) for 20 psf live load, 10 psf dead load, and L/240 deflection. It tells us that (if douglas fir is your preferred species) DF #1 2x6 @ 24"o.c. will span 12'-6".

Now you have twice the load (40 psf live, 20 psf dead) and need 2/3 of the deflection (L/360) compared to the table parameters. So you'll need to double the member count for the loading, and add another 50% to reduce the deflection. That means instead of 1 member per 24", you need 3 members per 24". Which is 8" o.c. on average, or 2 members at 16" o.c. That is, sister each hacked 2x8 with (2) 2x6 DF #1.

Cheers, Wayne

 

[ICE]

This is the table that was used when your dwelling was built. Given that the IRC has tables which specify DF#1... I wouldn't trust them. DF#1 is probably as good as DF#2 was back in the day. The other consideration is that pushing to the limit seems wrong. Maybe it's just me but going to all of this trouble for a couple of inches in a basement seems ....well odd.

I suppose that LVL 12"oc. with full depth blocking 3'oc. might be strong enough. There's only one way to find out. Please do tell us the result. Oh and you mentioned asking the local inspector....that could be a story all it's own.

 

[DIYBuilder]

Hi ICE, I agree I don't want to push the limit. I want to know what the limit is so I can stay a bit away from it. The reason I want to do this is to meed the IRC 7' height rule for finished basements. For that I need to raise the joists by at least 1". If 2" is at the limit, then maybe I'll just take of 1" to be on the safe side.

wwhitney, that's a good point about the grade of the lumber changing if I hack the bottom.
BTW, these will be floor joists (it is the basement ceiling = kitchen floor), so I would need table R502.3.1(2) (p. 139 of IRC 2018), 2x6 column dead load 20 psf, live load 40 psf.

 

[DIYBuilder]

One half of my basement is already sistered with 2x6 LVLs. My contractor did this a few years ago because the original joists were badly notched by plumbers in the 1930's. See attached picture! So for these old joists, cutting them up 2 inches will actually make the lumber grade better!
So can I cut 2 inches off these old joist up 2 inches?
Or if I sister both sides with LVL, then can I do it?

 

[ICE]

R305.1.1 Basements. Portions of basements that do not contain habitable space or hallways shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).

Exception: At beams, girders, ducts or other obstructions, the ceiling height shall be not less than 6 feet 4 inches (1931 mm) from the finished floor.

This has been a topic of discussion several times. It has been shown that jurisdictions have various opinions of ceiling heights in a habitable basement. There seems to be some that allow a lessor height for the reason that....well why not?.....are we going to deny the use a perfectly good basement for the lack of a few inches?

 

[steveray]

That's a lot of work and money for 2" of headroom...

 

[ICE]

So for these old joists, cutting them up 2 inches will actually make the lumber grade better!
So can I cut 2 inches off these old joist up 2 inches?
Or if I sister both sides with LVL, then can I do it?

So you've already done it with no problem? Why the concern now? And by the way, the blocking should be continuous. I guess these have no crown to speak of but for the sake of artistic expression I would turn them right side up.

 

[wwhitney]

BTW, these will be floor joists (it is the basement ceiling = kitchen floor), so I would need table R502.3.1(2) (p. 139 of IRC 2018), 2x6 column dead load 20 psf, live load 40 psf.

You've missed the point of my post.

On the table you referenced (the obvious first place to look), none of the 2x6 options work for a 12' span, even at the tightest spacing listed, 12" o.c. So you want to check whether a tighter spacing would work. The next simple multiple would be 8" o.c., which in practice you'd install as double members at 16" o.c.

Since the table doesn't cover 8" o.c., we need to be a bit more resourceful. If we halve the load, and halve the number of members, the load per member is still the same, and the allowable span is the same. So instead of checking 40 psf live, 20 psf dead, 8" o.c., we check 20 psf live, 10 psf dead, 16" o.c. Which the table I referenced covers. [The fact that it is for rafters rather than joists doesn't matter; it covers the case of a flat roof, which is the equivalent geometry to floor joists.]

Then an added wrinkle is that the 20 psf live, 10 psf dead table doesn't have the correct deflection criterion, it's L/240 instead of L/360 for floor joists. So again, if you just use 50% more members, you'll have 2/3 as much load per member, and 2/3 as much deflection, and the L/240 deflection criterion becomes an L/360 deflection criterion.

And the upside of the above reasoning is that it has a chance of convincing a plans examiner without having to hire an engineer.

Or if I sister both sides with LVL, then can I do it?

Certainly that would suffice. Since the tables show double 2x6 DF #1 would work, and an LVL is stronger and stiffer than DF #1.

Cheers, Wayne

 

[wwhitney]

So you've already done it with no problem? Why the concern now?

Because now he wants to cut off the portion of the original joists that hangs below the LVLs, which would weaken the system.

And by the way, the blocking should be continuous.

The picture shows continuous blocking. The old joists hang down 2" below the LVLs, so the perspective is a bit non-intuitive.

Cheers, Wayne

 

[DIYBuilder]

the left half the basement has the LVL's already. My contractor did this a while back. This is where I got the idea to cut the old joists up 2".
But I have not cut the bottom of the old joists yet because I don't know if it will be allowed.

 

[DIYBuilder]

Hi wwhiney, I'm still reading your post (several times) to get it.
BTW i just checked the span. The free span from wall to central beam is 10" 4"

 

[wwhitney]

an LVL is stronger and stiffer than DF #1.

To quantify that, BC's published design values for their Versa-Lam LVL 2.1E 3100 are an apparent modulus of elasticity of 2.0*10^6 psi, and an allowable bending strength of 3100 psi. While DF #1 design values are apparently (from a random plausible internet source) a module of elasticity of 1.7*10^6 psi, and an allowable bending strength of 1000 psi.

Note that the LVL provides a much bigger improvement in bending stress (3.1x) vs the improvement in stiffness (1.18x). So the LVL does quite well in comparably low span, comparably heavily loaded applications, such as headers and beams. While for a deflection controlled application like the OP's, the improvement is fairly modest.

Cheers, Wayne

 

[wwhitney]

The free span from wall to central beam is 10" 4"

So you want to measure the full length of the joist that isn't sitting on the wall and isn't sitting on the beam. Face of support to face of support.

If that's 10' 4" rather than 12', that makes a big difference. You're now back into the realm of the floor joist span table, and DF SS at 16" o.c. has an allowable span of exactly 10' 4". So you don't need to sister each member with (2) new members, you can just use (1) new member. Either DF SS or LVL. The span table doesn't cover LVL, but hopefully a plans examiner will accept than an LVL is stronger than DF SS, so is an acceptable substitute.

BTW, why do you specify 20 psf dead?

Cheers, Wayne

 

[DIYBuilder]

Hi Wayne (wwhitney), I think I am understanding your post now. Thanks!

Btw, I meant to say: the free joist span from wall to central beam is 10 feet, 4 inches, not 12 feet, so that helps the situation a bit.

So based on your analysis I conclude that one 2"x6" sister at 16" (as in the picture), then cutting the old joists up 2 inches ), is not worse (regarding both strength and (barely) stiffness) than the original one 2x8 joist at 16"

I realize this is just an opinion and not a signed structural design! It serves as a starting point for further analysis.
And I will ask my town inspector first, and show him this discussion if he is in doubt.
I may still need a stamp from an engineer.

Thanks for you analysis.

Btw, I have a Lally column "puzzle" question that I will post soon. I hope you will see it and comment some time.

 

[wwhitney]

So based on your analysis I conclude that one 2"x6" sister at 16" (as in the picture), then cutting the old joists up 2 inches ), is not worse (regarding both strength and (barely) stiffness) than the original one 2x8 joist at 16"

That's not actually what I said, I'm ignoring the contribution from the hacked up old 2x8s.

What I said in the last post was that if the clear span is only 10' 4", then the span table tells you that DF SS 2x6 @ 16" o.c. suffices for that. No engineer required for that conclusion. And I said that 1-3/4" x 5-1/2" LVL will be stronger and stiffer than DF SS 2x6. Which hopefully is just acceptable on its face without requiring engineering. Since you already have the LVLs on one side, I'd suggest sticking with those if possible.

Cheers, Wayne

 

[DIYBuilder]

I wanted 20 psf just to be on the safe side. I don't know what it means really. There is a kitchen and dining room on above the ceiling.