Scenario: “bonus” room over garage to be used as kid’s playroom. Span – 19’8″. Architect insists on using 14″ TJI 560s @ 16″OC(the rest of the floor in the house uses 2x12s). I insist that it will be sufficient to go with #2 Hem-fir 2×12 @12″OC (or possibly double them up @16″OC). Whot’s right? If more info is needed to make the determination, let me know…
Replies
According to the TrusJoist Application Guide, your architect is going a little overboard. 14" 560's are good for nearly 27' span, and that's at L/480 for 40 psf live and 20 psf dead load.
I'll attach the guide here. Span tables on page 4. It's a pretty big file, and trakes Adobe Acrobat to read. The second file is just the span table in .pdf format.
Jon
That's exactly my point! The house plan is actually for potential clients. I'm trying to save them some money here and there, so they can actually afford it! Not only is the architect overengineering things left and right, he actually made the house almost 1000 sq ft bigger than originally planned!
Lord knows I'm not a fan of architects...IMHO "architect" is Latin for "A__HOLE"..but is this bonus room in the attic space over the garage? Is there a knee wall coming down onto the joists? Maybe they are picking up more than just floor loads...
Depends on a couple of things - Like will the kneewalls support any roof load.
Offhand, I'd rather have something 14" deep. If you have time check out the thread on floor vibration:
http://forums.taunton.com/n/mb/message.asp?webtag=tp-breaktime&msg=21010.1
If more info is needed to make the determination, let me know...
Are the floor joists sized to support the floor load and partially support the rafters via knee walls? (ie Are the knee walls designed to be in compression?)
Are the rafters sized to support the roof load and partially support the floor joists? (ie Are the knee walls designed to be in tension?)
What is the architect using as his basis for the 14" 560 specification?
Jon
lil' bit different thinking too... I realize it is a bonus room over a garage. Is there any mechanical ducts running in the floor? He may have had to have the deeper truss joist to accomodate the mechanical system?
cler
I think that the Archi is correct. We have a plan that we span 22' with 14" I-joists 16" oc and it could be stiffer in my opinion and it is drywalled with 5/8" underneath (bonus room). I think that the small amount of money you would save, isn't worth the "insurance" that the 14" joists provide.
Just my $0.02 :-)
I would spend the money on the TJI's. Much stiffer floor and you have a product manufactured under controlled specs that you know won't have any knots or splits.
You will really feel the difference in the floor.
I've used both tji's and 2x12's for similiar spans.
Nobody will be happy if you use the 2x12's - 12" oc.
To much bounce in the finished product, tight conditions for ductwork and wiring. If you are using fb insulation, much harder to insulate. If the ceiling is finished below, drywall cracks will be a continous thing. On and on.
Terry
I think that you could find a 12" Tji that would be sufficient. I would not use regular framing lumber for this span. You will notice a fair amount of vibration. For me, in a kid's playroom, this would be acceptable. In the main living area, I would spend the extra money and get deeper joists or find a way to cut the span.
the 14" TJIs are the better product, and there is no way that you will save the client money by using that many pieces of solid lumber and the labor involved to put them in whne compared to the TJI setup. You'll have twice the labour in the solid lumnber
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