Floor Joist Beam Spans

James · 2006-07-08T17:36:24+00:00

I plan to build a small garage, 20 feet by 30 feet. I want to be ableto span the 20 foot width, so that I don't have to use interior posts.At first, I was doubtful this could be done, and I have seen comments inthese groups that this is not really feasible. Yet, I have closelyinspected one of the yard sheds (with loft) at Home Depot, that is 16 feetwide, using 2 x 10 beams on 12 inch centers. It is a yard shed, with asmall loft. I went up into the loft area to see what "bounce" the floorhad, and it is quite solid, with just a small hint of a bounce (I weigh215 lbs). So, I have concluded that spanning 16 feet with 2 X 10'sis easy, as I have seen it.But, I know that going from 16 ft to 20 ft wide is 4 feet more ofspan and is 25 % more of a span. I am a novice, but I try to findanswers for myself first. Somehow, I got a span table for Southern Pinelumber. The title of the chart isMaximum Spans: Souther Pine joists and rafters .This is the full name.The chart also says: 40 lbs psf live load/ 10 lbs psf dead load/240 deflection / cd = 1.15I plan to use the loft only for very light storage, but these "load"figures seem very low to me. But, once again, I have "felt" what a 16ft span using 2 x 10's feels like, and it seems very sturdy to me.From the chart, it appears that a # 2 visually graded (is that what you"usually" find in lumber yards and the big box stores??) 2 X 10beam on 12 inch centers will span 19 ft, 11 inches.A 2 x 12 beam on 16 inch centers will span 20 ft, 2inches.-----------------------Questions: First, am I on the right track ? Does the chart seem to applyto my needs and plans? I could email the chart (pdf format) to anyone whowanted to look, I don't think I should post an attachment here on a newsgroup.Is #2 visually graded, the most common lumber found in lumber yards ?Which would be better, 2 x 10 on 12 inch centers or 2 x 12 on16...

Jul 08, 2006 42 Replies

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crhras 20 years ago

Right, that's exactly what I was saying.

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jusair 20 years ago

crowned spanning the 20 ft in the center of the 30 ft span then run joists perpendicular to the beam giving you a span of only abot 14'9 or 14' 7.5

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JimL 20 years ago

Nice picture.

I had a 30 year old house with cracks running across the ceiling and did what you did as an addon to stop the sagging.

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