I-Joist Questions
We are in the process of shelf building a 20x36ft two story house. Our plan was to use 11 7/8 L/480 I joists to span 20ft 16oc, however, after reading through various forums, it sounds like 18’ would be the max span for 11 7/8 I-joist, even through they pass at a 20’ span on the charts the floor might be pretty bouncy.
Should I size up to 14” I-joist 16oc?
My next big question is, we are going to install a wood cook stove in the center of the house. Given that a 10” OD triple wall stove pipe requires 2in of clearance, a 2 1/2in flange on the I joist would only give 1.75in of clearance on each side with the joist set 16oc. If we sized up to 14” and the joist flange widens to 3 1/2” that would give us even less clearance. How would a stove pipe be installed in this case? Would I be able to adjust the spacing between the two I-joist where the stove pipe would run through to make it a little wider than 16oc? Or is there another solution?
Thanks in advance.
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Metalbestos is smaller.
Is the downstairs free of walls?
It has been over 20 years, but my last house, I think had TJI and they spanned either 22 or 24 feet, and ISTR the design conversation being we don't use 2x12s anymore. It was garage under with an 18 foot garage door with TJI parallel, so at least 22 feet.
Floor didn't bounce.
No walls in garage, but walls upstairs
It’s an open floor plan, walls are limited to a short hallway, small bathroom and a closet.
FYI, here in NH we could not use I-joists for the first floor in a house built on a full basement without installing a drywall ceiling below (IRC 2018/2015 section R302.13 requirements). (I'm assuming you'll have a basement since you're in Maine, but that may be a bad assumption.) Whether or not your AHJ enforces that requirement is the big question.
I opted to use TriForce's open joist floor trusses which have a 2-foot field trimmable section at one end. The trimmable end has an OSB web between the top & bottom chords which would technically have to be clad with drywall to meet the IRC requirements, but that's not a huge effort. Their OJ315 model comes in a 20-foot version with a 2x3 for the top & bottom chord.
That said, it should be possible to slightly shift the I-joists to provide clearance for the chimney - but obviously that's something you'd want to pass by an architect/engineer.
MaineHomestead,
Move the TJ or block out the opening much as you would for a toilet that falls over a joist. Depending on where the chimney is on the span you may or may not have double up the TJs on each side. The supplier should have a standard detail in their installation instructions.
I recently built that (20' with wide flange 11 7/8 on 16). Wasn't bouncy but it was an upper story with bedrooms/bathrooms. Did use 7/8" OSB though.
It will work mostly for an open plan except if you have a large island. There I would decrease the spacing or double them up.
Most I-joist manufacturers allow an offset in spacing for a single joist to accommodate drains and other utilities.
Sorry, I wasn’t clear. The house is built on a slab so the I-joists are for the second floor. There will basically be one wall down the middle of the upstairs dividing it into two bedrooms and there will be a few closets.
TJI 360s are rated for a 20'-11" span and TJI 560s are rated for a 23'-8" span, at 16" o.c. and L/480 deflection. Code only requires design for L/360 deflection but I have found that with longer spans, L/480 makes for more comfortable floors. And that's for a 40 psf live load; bedrooms are only required to have a 30 psf live load, though many designers and engineers use that for second-floor bathrooms as well, I stick with 40 psf on the second floor to be safe.
That is, if you're in the USA. In Canada they take potential vibration into account as well, but that should only be an issue if you're close to the maximum load, which you wouldn't be in a bedroom. But I'm assuming from your screen name that you're in Maine.
It's ok to adjust joist spacing, up to 24", as long as the on-center layout remains 16" o.c. otherwise.
https://www.weyerhaeuser.com/woodproducts/document-library/document_library_detail/tj-4000/
Great, thanks for the replies! Really appreciate everyone’s input!