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Ceiling Joist size needed

2891 Views 3 Replies 2 Participants Last post by  bergenbldr
I am building a room inside a garage bay. The room needs to be 18' wide on the inside. The length dimension will be 18'-29', still undecided about how much room I require. I will be using OSB I-Beams for joist (?silent floor joist?). I need to know what width of I-beam will be required to span the 18'. The ceiling load will be 5/8" sheetrock, the I-beams (of course) and 3/4" plywood. There will be light duty storage on top of this, no more than 20lbs/sq ft. and probably a lot less. This will be on a concrete floor and probably 2 x 4 construction, possibly metal stud. Thank You.

Leo G
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the i-joist manual provides installation details and span tables .L/480 is the recommended spec for residential may need to consult an engineer if you have an unusual situation that the manual does not address .
Engineer contacted

I contacted an engineer and he said that it would take a 11 7/8" @ 16" OC or 9 1/2" @ 12" OC for a 40lb/sq ft load rating to span the 18' that I need. Standard residential rating. Thanks.

Leo G
just a note. the reason for the higher L/480 spec is mostly due to the total deflection at longer spans and not overall live and dead loads. a 20ft span at L/360 has an allowable deflection of almost 3/4 in",this probaly unaceptable.make sure your eng is using the L/480 spec as this is the manufactuers recommendation.
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