I plan to build a small garage, 20 feet by 30 feet. I want to be able to 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 in these groups that this is not really feasible. Yet, I have closely inspected one of the yard sheds (with loft) at Home Depot, that is 16 feet wide, using 2 x 10 beams on 12 inch centers. It is a yard shed, with a small loft. I went up into the loft area to see what "bounce" the floor had, and it is quite solid, with just a small hint of a bounce (I weigh 215 lbs). So, I have concluded that spanning 16 feet with 2 X 10's is easy, as I have seen it.
But, I know that going from 16 ft to 20 ft wide is 4 feet more of span and is 25 % more of a span. I am a novice, but I try to find answers for myself first. Somehow, I got a span table for Southern Pine lumber. The title of the chart is
Maximum 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 = 1.15
I 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 16 ft 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 10 beam on 12 inch centers will span 19 ft, 11 inches.
A 2 x 12 beam on 16 inch centers will span 20 ft, 2 inches.
Questions: First, am I on the right track ? Does the chart seem to apply to my needs and plans? I could email the chart (pdf format) to anyone who wanted to look, I don't think I should post an attachment here on a news group.
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 on 16 inch centers ?? It seems that the latter may be a bit cheaper, but price isn't the primary concern.
What happens if you use a 2 X 12 beam, but put them on 24 inch centers instead of 16 inch?? Do you simply get more deflection, and less load capacity ?
I know I could use an engineered beam, but I don't want that.
Thanks for any tips, experience, and advice !!!!