MopardudeWI
Well-known member
Can anyone recommend a good source for figuring out I-joist size for ceiling? I need to span 20ft, 24in OC if possible, no attic space above, and insulation and most likely ribbed pvc panel for covering.
Figuring out ceiling joists.
- Thread starter MopardudeWI
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Skiff Builder
Well-known member
WNYflyer
Well-known member
Go to your local lumber yard who handles I-joists and talk to them and if they can't help you answer that question find out the brand they handle and contact that brand's technical help. Given that it is a ceiling and assuming there is not going to be any type of sheeting diaphragm up on top to brace the I-joist from buckling under bending then you would probably need lines of some type of blocking placed perpendicular to the joist and spaced so many feet on center. Blocking would need to be sufficiently anchored at its ends. Probably not going to find this situation in any of the manufacturers typical literature so best to contact technical help. Probably best to figure out the dead load of the panel, insulation, etc in psf (pounds per square foot) before you contact them since that will probably be helpful to them and of course the span and spacing information.
firebirdparts
Well-known member
It'll be the smallest one they make, whatever that is. A 2 x 8 is required if you use ordinary lumber and I would think they don't make an i joist that weak.
OP
MopardudeWI
Well-known member
I had the same thought, I actually just got back from there. They were not much help other than I was able to get the brand they use to use the proper chart. Back in the 90's I used to go to school for drafting. I could have sworn we had generalized charts that were not so brand specific but I maybe wrong on that.
I guess what I am not understanding here is if you just do a general search for span tables using lumber, they break it down real easy with or without drywall and if their is attic space above or not. A 2x8 #1 grade will do what I want. I work in the trades but I mainly do trim carpentry, custom built cabinets and such. Framing guys have always led me to believe I-joist are way stronger than traditional lumber. Looking at these span tables for them I am not seeing how they even can say that.
40psf Live and 10psf dead seems to be the standard load ratings all these I-Joist charts use. Since my ceiling and walls are all inside the polebarn structure. Do I need to factor in anything for a live load so I can bump down to a smaller joist size? Assuming the ceiling materials end up weighting more than 10psf?
OP
MopardudeWI
Well-known member
That is what I am seeing too for regular lumber. For I-joists it doesn't seem like they make them strong enough for that span if i am looking at this right.
Didn't quite a few issues come out recently in regards to "I-joist" style materials?
People getting sick from the chemicals, fire resistance, etc? I remember reading something about it after we had an attached garage built. The builder was not a fan and after almost 30 yrs in business, never used them. My garage second floor joists and rafters are all 2x12's.
Google it, before you make up your mind.
People getting sick from the chemicals, fire resistance, etc? I remember reading something about it after we had an attached garage built. The builder was not a fan and after almost 30 yrs in business, never used them. My garage second floor joists and rafters are all 2x12's.
Google it, before you make up your mind.
Toolfool
Well-known member
I know I've done 30' (probably more like 29') span 16"oc with 9" TJI ceiling joists with 1x4 cross bracing at 10' and 20'. 1/2" drywalled lid , R38 blown-in insulation. Done according to engineered plans.
WNYflyer
Well-known member
https://up.codes/viewer/new_york/irc-2015/chapter/8/roof-ceiling-construction#R801
New York State Residential Building Code which is based upon the International Residential Building Code. The International Residential Building Code is the starting point for all State Residential Building Codes I believe.
Section R301.5 indicates the minimum live loads ceiling/attic space needs to be designed for along with of course the dead loads.
For normal lumber Section R802.4 gives the required ceiling joist size for dead load live load combinations.
All the I-joist literature I am seeing are for floor loadings ( i.e. 40 psf Live Load) and assumed with sheeting down to brace the joist. If you really want to use I-joist you really need to contact tech help at the manufacturer for your specific conditions. And remember if stuff can be put up top someone will probably do it if not now then probably in the future.
firebirdparts
Well-known member
They don't make them weak enough (for a ceiling). They were never really intended to be used for ceilings, I guess.
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WNYflyer
Well-known member
I see were you said this structure is going inside a pole barn. Keep in mind that you may need full or partial sheeting up top to laterally stabilize the structure. PVC panels on the ceiling can't be counted on to supply any lateral stability to the structure.
OP
MopardudeWI
Well-known member
Yea you guys are probably right. Based of what I am seeing here they really don't give clear cut ceiling joist charts like. The only reasons I was leaning towards I-joist was I was under the impression they were both cheaper, smaller, and lighter than going traditional lumber. Perhaps the big expensive houses I am normally working in, on that scale maybe it makes more sense than. Based off what the lumber company gave me price per foot today and what these charts are saying 2 of the 3 reasons why are not even true for my application. Plus I believe you are probably right about having to sheath it if I do, because I am not seeing any other info on how to cross brace it. With how they have the trusses braced currently in my shop to have to sheath the top side would be a nightmare to try to do by myself.