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Old 11-24-2008, 09:28 PM   #1
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your choice of floor joists material..


when i was looking up construction information, i noticed their are a number of choices for floor joists, LVL, those i beam things with the osb, standard 2x material, etc, what material is strongest for floor joists?
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Old 11-24-2008, 09:34 PM   #2
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your choice of floor joists material..


It all depends on the span really. I like "I joists". They are light and you can have then made to almost any length. Floor trusses are also cool if you have trouble nailing a 1 1/2" peice of wood but they are quite a bit heavier.
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Old 11-24-2008, 09:36 PM   #3
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your choice of floor joists material..


It all depends on the floor system. Some times one will differ from the other in the same situation. "I" joist systems are supposed to be extremly strong as floor joists(stronger then dimenstional lumber) especially when spans are very long. LVLs are extremley strong to but you usually dont see thosed beeing used as floor joists, mostly beams, headers, girders and other applications with very long spans or a very heavy weight bearing load.
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Old 11-24-2008, 09:41 PM   #4
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your choice of floor joists material..


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Originally Posted by CrpntrFrk View Post
It all depends on the span really. I like "I joists". They are light and you can have then made to almost any length. Floor trusses are also cool if you have trouble nailing a 1 1/2" peice of wood but they are quite a bit heavier.
floor trusses? ive heard of ones for ceilings, but this is the first ive heard of floor trusses, you wouldnt know where i could see a pic of one would ya?
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Old 11-24-2008, 09:45 PM   #5
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your choice of floor joists material..


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Originally Posted by kevin211mvd View Post
It all depends on the floor system. Some times one will differ from the other in the same situation. "I" joist systems are supposed to be extremly strong as floor joists(stronger then dimenstional lumber) especially when spans are very long. LVLs are extremley strong to but you usually dont see thosed beeing used as floor joists, mostly beams, headers, girders and other applications with very long spans or a very heavy weight bearing load.
stronger than dimensional lumber eh? i like that, are they available in lengths of 28 feet, and do they need any support underneath like a girder(whatever those 3 layers of 2x12s nailed together are) or metal posts or anything?
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Old 11-24-2008, 10:23 PM   #6
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your choice of floor joists material..


Here's a link to floor truss info.
http://www.sbcindustry.com/images/pu...ct%20sheet.pdf
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Old 11-24-2008, 10:33 PM   #7
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your choice of floor joists material..


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stronger than dimensional lumber eh? i like that, are they available in lengths of 28 feet, and do they need any support underneath like a girder(whatever those 3 layers of 2x12s nailed together are) or metal posts or anything?
You're really oversimplifying a very complicated design process. Yes, a span of 28' (in any depth of residential I-joist) will require a center support beam.

What are you working on?

Don't rule out good old dimension lumber. I-joists and floor trusses have their advantages, but one major downside to them is fire. Either will fail in no time in a fire, whereas dimensional lumber will last much longer since it chars and retains much of its structral integrity for much longer.

A major advantage to floor trusses is the ability to run mechanical, electrical, and plumbing perpindicular and up in the joists instead of beneath them.

I-joists are capable of slightly longer spans than dimension lumber, given similar depths. When overspanned however, they'll bounce or fail just like any other floor system.
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Old 11-24-2008, 11:29 PM   #8
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your choice of floor joists material..


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What are you working on?
im designing a house, its nothing fancy, just a simple one bath 2 bedroom, with attic and maybe a basement(the basement might be considered fancy because i like secret spaces and highly paranoid, so a good portion of it will be a hidden panic room, and i might decide to put a bathroom in that area, so i guess its a 2 bath house), its the one that ive been asking questions on here for, with the roof and things that you and others have been giving me advice for,

here is an example of the house, i know some things from drafting and carpentry class, but that was a long time ago, so im trying to fill in blanks with the advice users on this board give(and after this i might do another design for a house or do one for the medical practice my mother will be setting up when she gets her nurse practitioners license )
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Old 11-25-2008, 07:56 AM   #9
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your choice of floor joists material..


A 28ft span can be done without any support under it. I-joist's or floor trusses can do this. BUT, the floor system design should be done by an engineer. This however isn't a big deal. Most I-joist distributors provide this service. And, floor trusses are almost always designed specifically for the job.

With that said, I would still consider putting a girder or load bearing wall in the basement. You'll likely need less building material.
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Old 11-25-2008, 09:33 AM   #10
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your choice of floor joists material..


28' clear spans are VERY UNCOMMON in homes. It would take at least a 14"...Probably a 16" deep joist, and the on-center spacing would likely be closer together than 16". At 28' clear span, most any wood floor will feel like a trampoline.
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Old 11-25-2008, 12:38 PM   #11
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your choice of floor joists material..


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28' clear spans are VERY UNCOMMON in homes. It would take at least a 14"...Probably a 16" deep joist, and the on-center spacing would likely be closer together than 16". At 28' clear span, most any wood floor will feel like a trampoline.
Yes, it is very uncommon. But, some people do it. Meeting deflection criteria at those spans isn't too big of a deal. But, as thekctermite pointed out vibration is a bigger issue. Just out of curiosity I ran some numbers through Louisiana Pacific's design software.

The minimum to meet both L/480 deflection and NRC vibration criteria is 20" LPI36 joists space 12" o.c. This also requires strapping, blocking, and 5/8" drywall on the joists. That's a lot of big joists. You'd be happier if you put a girder or load bearing wall in the basement. It'll come out cheaper and the floor will likely perform better. Either way, if you decide to go with i-joists, have the i-joist distributor or an engineer provide the layout. Some places will do this a little to no charge when you buy the joists.
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Old 11-25-2008, 01:22 PM   #12
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your choice of floor joists material..


in the basement, i was thinking of having a wall roughly 16 feet from the front wall, and roughly 12 from the back(ive been working on something in my mind for a secret door), im guessing i will need a girder 12 feet from the front wall even with the basement wall, would that be good with dimensional lumber or i joists? would i need to shorten the space between the joists or would the standard 16 oc work?

(i plan to do the layout of the joists and things on graph paper after i get my first end wall done ,)
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Old 11-25-2008, 01:58 PM   #13
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your choice of floor joists material..


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Originally Posted by feralfreak View Post
in the basement, i was thinking of having a wall roughly 16 feet from the front wall, and roughly 12 from the back(ive been working on something in my mind for a secret door), im guessing i will need a girder 12 feet from the front wall even with the basement wall, would that be good with dimensional lumber or i joists? would i need to shorten the space between the joists or would the standard 16 oc work?

(i plan to do the layout of the joists and things on graph paper after i get my first end wall done ,)
With the wall offset 2' from center the joists become much easier. I don't see any reason to add the girder on the other side.

To show how much this changes things I ran this through the software again. This will require 11.875" LPI20 @ 24" o.c. and 23/32" sheathing nailed and glued. Again this meet L/480 deflection and NRC vibration criteria.
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Old 11-25-2008, 03:11 PM   #14
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your choice of floor joists material..


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With the wall offset 2' from center the joists become much easier. I don't see any reason to add the girder on the other side.

To show how much this changes things I ran this through the software again. This will require 11.875" LPI20 @ 24" o.c. and 23/32" sheathing nailed and glued. Again this meet L/480 deflection and NRC vibration criteria.
what is lp120? im not familiar with things like that

what would be the cost for these floor joist choices? im not looking for a specific number, i understand that in different places and in different stores materials costs can vary
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Old 11-26-2008, 09:23 AM   #15
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your choice of floor joists material..


LPI20 is the series of the Louisiana Pacific joist. Each manufacturer has different types of I-joist series that have different load handling capabilities. For example, 16" high LPI56's are stronger than 16" high LPI20's.

To give you an idea of price, I just paid approximately $65 a piece for 32' long 16" high iLevel TJI230's.
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