I have an addition that is to be built for a homeowner who wants I-joists. I&#;ve gotten MUCH conflicting info between my Lumberyard and the Big box stores as to the right size joist.
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The big boxes are spec&#;ing Boise Cascade I-joists. The homeowner says they want to feel the floor as solid as possible with as little hint of deflection as possible.
The structure in question here is 20ft 6&#; long x 28ft wide. I plan to space I-joists 12 o.c across the width of 28ft for a total of 26 I-joists. I&#;m using 11 7/8&#; I josits. The span that they must span is of course 26ft 6&#; (this span includes the foundation wall, outside to outside).
The owner plans for carpet on the floor, maybe wood. A possible large typical aquarium, typical furniture and chairs (this is a Sunroom). The upstairs floor, which mirrrors the first, will be a master BR consisting of typical BR furnishings like a nice heavy bed set.
I&#;ve been told I can get away with a BCI 90 which is a 3.5&#; top/bot cord of the joist. I also been told I can do it with a BCI MINIMALLY, or that I can use a BCI . One places says I&#;m told by the others wrongly. One place says I MUST use a 3.5&#; cord. Other places say I must use web stiffeners.
Any opinions out there on who is right? One place claims the mfgr says I must use 3.5&#;. I don&#;t know who to believe. The price difference is almost double between BCI and BCI 90.
If at first you don&#;t succeed, try using a hammer next time&#;everything needs some extra persuasion from time to time. -ME
My floor joists don&#;t need to hold insulation (unless I add some later for sound insulation) because my crawlspace has insulation outside the stemwall.
I could use 2x8s at 16 o.c. and spend $612 on lumber. Or I-joists 9.5 inches deep, 24 o.c., and spend $894.
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-Are I joists kinder to the planet? In terms of trees used it seems like yes, but what about processing footprint?
-Are I joists a lot easier to use? I know they&#;d be lighter and more uniform than 2x8s. 2x8s can vary a bit in depth, but it seems relatively easy to modify the depth at the joist hanger if necessary so that all match. More annoying to deal with: twist, bow, cupping, etc. Might it come down to the quality of lumber I can get? I can get kiln dried 2x8s. I know to put all joists crown up.
-cost of hangers seems comparable. I&#;m hanging the joists from the sill plate using top flanged hangers, which apparently has the advantage of eliminating a rim joist, which is apparently expensive for I-joists.
-2x8s give me a little more headroom in the crawl space. but I&#;d still have about 30 inches even with the I-joists.
-the joists will be ~18 feet long, with a beam to support in the middle. Plans don&#;t seem to make clear but I assume the beam is under the joists, not at the same height (so not requiring joists to be cut).
-since crawlspace is conditioned, I think plumbing and electrical won&#;t have to be punching through the joists. (I believe I joists are easier to poke holes in than 2x material.)
Are there other things I should consider? I look forward to getting some more perspectives.
Thanks everyone!
Paula
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