Floor Joist Span

BuriedHammer

Hi everyone,

Been checking out the forum for some time, and already gained a lot of knowledge here. Thanks!

Anyway, for my first post, I would like to ask your opinion and/or experience about floor joist span:

I'm getting ready to start a house that will have 2x10 #1 Southern Yellow Pine joists. It's a ranch house with truss roof for a typical 40/10 floor load (no load-bearing interior walls). The span table allows a maximum span length of 16'-9" @ 16" O.C. at 360 deflection in this usage.

The house is 32' front to back, with one beam down the center, so the actual span will be approx. 15'-5". The homeowners do not want two beams in the basement and I have not told them we are near the limit of the allowable span.

While it is allowable, I'm not sure this floor will feel stiff enough to satisfy the homeowners. I would rather go to 12" centers than have too much floor bounce. The longest span I ever went with this joist was about 14' and it was fine.

What do you think?

Thanks,
Chris

KentWhitten

16" OC's give you about 1/2" deflection. Going to 12" OC is not going to make a huge difference with that span.

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cleveman

I think you'll be fine.

I have spanned 16' with douglas fir, and 12' with a 2x8, both 16" OC.

Use adhesive with the sheathing. If you want to stiffen it up, put in two rows of solid wood blocking. I did this with a 2x6 floor spanning 12', 12" OC and it is way stiff.

JumboJack

Wow.Things sure are different around the country.I California you can't do any type of room addition/major remodel with out enginered,aproved plans.You can't even pull a permit in most cases unless the plans are stamped by an engineer and have gone through plan check.
I am sure it has a lot to do with the seismic stuff we deal with.

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in texas with framing and cornish people will do it for 3.00 a foot. What do yall think about that? Just laber

reveivl

You can also stiffen the joists a great deal by gluing and screwing a 2x4 on the flat to the bottom of the joists.

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FramingFanatic

Another idea would be to use a thicker subfloor

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thom

You will stiffen it a bit by gluing the sub floor. You could get even more out of it with TJI's or trusses.

Tom M

What do you mean? Is this new construction and you are considering altering the plans to split the spans into thirds instead of the mid span support(15'-5"). 15 FT sounds fine. 12" centers better and thicker T&G better yet.

Tom M

TGI's with glued subfloor like Thom says. Whats on this plan?

neolitic

Don't they sell 16' 2X12's where ever you are?

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Heritage

It's probably a design issue.

I don't have any numbers for #1 Grade...any species.

My charts are only for #2 and #3 Grades.
As for Pine there is:
Lodgepole
Ponderosa
Sugar

16"oc, with the sturdiest species of the one's above (Pnderosa #2) is 14'5".

If it comes down to the old debate of 12"oc or TJI's...you're almost always better off going with the TJI's.

We have done this math before.

You really have to get into the cost/benefit ratios here.

From what I'm understanding your beams are running front to back with a beam in the middle...right? Is going side to side a better alternative? Does the design allow for such a thing? You have probably already figure "NO"...but it's worth asking.

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WhitlockConst

I've done 14' span with 2X10 joists. The actual building span was 28 feet, but I broke them up with a glued and laminated beam that was about 16" deep. I used 3/4" OSB flooring and it is extremely sturdy. I've had help jump on one side of the floor as I stood and it didn't even shudder.





In my own opinion, I think you could get away with it, but you are definitely at the span limits.

Just tried inserting some pictures... Guess I need about ten more posts.

Rick2008

The spans in the tables you're talking about are usually over-engineered. Go with it. On the other hand, floor bounce is a subjective matter. What's too bouncy for one is fine for another.

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BuriedHammer

Thanks for all the replies, I appreciate your input.

cmansmith

I Have run into this problem many times in my framing career. The solution that gave me the best result was to nail blocking in between the joists right down the center. snap a line nail the blocks and then glue and nail the flooring to the blocks as well as the joists. This is something I always do regardless. Even before you lay the floor you can stand in the center and tell the difference.

8ft2by4

I ran your setup through our engineering software and it just barely passes at a live load def. of 360 and total load def of 240. And that is if you go 12 oc. It wouldn't pass at 16 oc. That is the statutes for the IBC. UBC is more strict. My suggestion would be to use 11 7/8" 210 series TJIs. You will get to go 24 oc instead of 12 and it will be a stiffer floor and most likely be cheaper. I get 210s for under a buck a foot in my area. Let me know if I can run any other options for you.

Aaron

beanders

My house is very similar, 30' x 42'. We have a steel beam in the 42' direction and #2 2"x10" joists sitting on top of it in the 30' direction, so they span slightly less than 15'. There is no blocking and there is an unfinished basement underneath so there is no lateral support between the joists. There is only one location in the house where there is bothersome "bounce" and that is a location where there is a heavy wardrobe/entertainment center placed parallel to the floor joists near the center of the span. We will probably add some blocking between the joists before we finish the basement to help stiffen it up a little.