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grover
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# Posted: 21 May 2013 22:53
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What does code have to say about how far the floor joists have to overlap in the middle of the floor. This is a 24 ft wide cabin with a beam down the middle. Probably will use 2 x 12's but if I get 12 footers they will only overlap 3 inches. Do I need 14 footers or can they butt up together end to end and scab a piece onto the side connecting the two?
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toyota_mdt_tech
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# Posted: 21 May 2013 22:57 - Edited by: toyota_mdt_tech
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I believe its 2 feet, a minimum of a foot on each side of the support beam under the splice for a min total of 2 feet. You will want to add blocking between the joist at the splice also.
3" I know wont work, get 14 footers, then just use the full 2 extra feet on each side for a total of 4 feet of overlap. There is a certain amount of nails to tie the 2 halves together too.
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ICC
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# Posted: 22 May 2013 01:16 - Edited by: ICC
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3 inches is IRC minimum overlap. that does work. it is what i would do. of course if you buy 14's and use 6" or so overlap you then have the blocking parts, assuming joists on 16" or less centers.
R502.2 Floor Design and construction. the entire codebook is there for free, no guessing
much more than 6 inches overlap is not required or needed. lots of overlap is bad too as that can lead to the overlapped ends moving up slightly if loads on the center of the joist cause the joist to sag slightly. can make squeaks between the faces of the joists.
and yes, solid blocking, same depth as the joists is required between the joists directly over the center beam.
butting the joists would be permitted with scabs but an overlap is easier and quite alright to do.
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ICC
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# Posted: 22 May 2013 01:24 - Edited by: ICC
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also quite valuable is the nailing schedule; how many of what size nail to be used for different purposes.
TABLE R602.3(1) FASTENER SCHEDULE FOR STRUCTURAL MEMBERS
note nail sizes are given in "D's" as well as actual physical dimensions. if using a nail gun watch the diameters and lengths as menay nail gun nails are actually "box nail" sizes, not the "common nail" sizes that are listed as code. usually 50% more box nails will cover your use of box instead of common.
two - 10d (3″ × 0.128″) nails are all that is needed at the joists overlap. face nailed one joist to the other. plus toe nailing to the beam; 3-8d (2 1/2″ × 0.113″)
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ICC
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# Posted: 22 May 2013 01:52
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look at it this way. the girder, the beam, is what supports the floor joists, not any amount of joist hanging over the girder in mid-air. the ends of the joists out at the outside end only require 1.5" of bearing surface if bearing on wood or metal (metal = joist hangers). theoretically as long as the beam was 6 inches wide and the joists butt ended exactly over the center of the beam that would be fine as well.
many builders will overlap the joists by more than a few inches because that is the lazy way out. no cutting, just throw the joists in there and be done. not necessarily the best way.
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grover
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# Posted: 22 May 2013 22:05
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Sounds like anywhere from butting the floor joists together with a 2 x 12 scabbed to the side to overlapping them by a 3 inches to a couple of feet will work as long as they are properly nailed and blocked in between.
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grover
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# Posted: 22 May 2013 22:51
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This may be a stupid question and I may be over thinking things but try to follow my mind. If the floor joists overlap then you will have the center of the 6th joist at 48 inches on one side of the floor and 46 1/2 or 49 1/2 on the other side of the floor. Not sure if that makes sense or if I have this all wrong. Sounds like butting them end to end would solve this issue. How does the overlapping joists work with the sub-floor?
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Truecabin
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# Posted: 23 May 2013 11:08 - Edited by: Truecabin
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good you are now thinking right
that lap joint bs is for experienced contractors who can save time because they can deal with it on 5 identical structures but you already wasted that time trying to do their tricks
butt your 12 footers together over the beam with a 2foot scab
your nail lines will be straight and on 16s and no guessing
your 4x8 sheets will nail straight. it will all work better.
the scab joint is stronger than the rim because its sitting on the beam
dont waste a minute worrying about squeeks its not gonna squeek
squeeks are b.s. that a contractor has to worry about but not you who cares if there is a squeek dont step there if you dont like it
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grover
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# Posted: 23 May 2013 17:29
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I thought about the numbers I wrote and wanted to correct them so they don't totally confuse someone. It would be the 6th joist over (16 inches on center) at 96 inches on one half of the floor and 94 1/2 or 97 1/2 on the other half of the floor.
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ICC
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# Posted: 23 May 2013 19:48 - Edited by: ICC
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When using overlapped joists you start the floor sheathing from one side and end corner. When you come to the overlap you use some of the scraps you will likely have to place scabbed on nailers where needed because of the offset. Then shift the next full sheet to lay over, line up on the joists and carry on from there.
:D Quoting: Truecabin squeeks are b.s. that a contractor has to worry about but not you
As for squeaks I didn't know they only happen to contractors and not DIYers.
Quoting: Truecabin if there is a squeek dont step there if you dont like it
tell that to your wife :D
maybe i think too much and try to make things as well and as correct as possible; especially when the only cost is thinking and then cutting materials to a more practical size?
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MJW
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# Posted: 23 May 2013 20:34
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Quoting: ICC As for squeaks I didn't know they only happen to contractors and not DIYers.
I took every precaution I could to avoid squeaks.
Adhesive on every joist under the Advantech, screwed the subfloor instead of nailing, roofing paper between the subfloor and actual flooring and plenty of nails in the flooring.
For the most part, it worked but even with all that we get a squeak from time to time. Wood expands and contracts. It is going to happen.
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Truecabin
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# Posted: 24 May 2013 01:53 - Edited by: Truecabin
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whiny customer can make a contractor jump thru hoops but not the DIY
Its not really the squeek its the satisfaction of making somebody dancd for you thats what some people are like
by the way are you folks builing a cabin or a recording studio?
2 foot scab is the obvious way for this non problem
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