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I’m building a duplex that is 56 ft wide. I plan to use I-joists. Should I (1) use 56ft I-joist or (2) lap shorter I-joists(2-30ft I-joists) at mid-span beam? Is it a common practice to lap I-joists or is it better to use one continuous length? Thanks
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tom,
if this is a duplex , you will have to seperate the two units with a firewall, so you can't run them the full length or even lap them on a beam.
you might be able to do it with a common basement , but the upper floors are doubtful.
I would check the codes very carefully. if you are in a no inspect area, I would still follow code.
as for the actual structural strength, a 56' I-joist would have to be very deep to be strong enough, if it is even available that long.
even a 30' I-joist is deep.
*I doubt you'll find I-joists 56' long - the longest I've ever messed with were 48'. Once they get over 40', they're pretty floppy and hard to handle. Bill makes a good point about the firestop, also.
*tom... butt over a mid-span beam.. why would you lap them?
*I believe 60' is the longest you can get them as a "standard" length. That's the way it was when I first investigated them years ago. Haven't come close to that length with TJIs, but have with LVLs.
*I built a house a few years ago with 50 footers. Kinda a pain to roll. You can butt em over your beam.Why aren't you asking your carpenter and supplier what they prefer?
*Tom,What Bill said is correct. The fire codes basically imply that, if one part of a duplex burns down, the other side has to still be structurally sound. So, like one wall can't support a roof member from both roofs or one joist can't be common to both sides. Darrell
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I'm building a duplex that is 56 ft wide. I plan to use I-joists. Should I (1) use 56ft I-joist or (2) lap shorter I-joists(2-30ft I-joists) at mid-span beam? Is it a common practice to lap I-joists or is it better to use one continuous length? Thanks