Hey!

So, I am building a workshop ... have a 52 x 64 pad poured.

It is divided into three 21 ft - 6 in bays.

I have a storage attic above the center bay.

Lumber, machines, .... all heavy things to be stored.

So, 2 x 12's won't work.

I used a tji calculator .... 16" 360's

I would like to know if maybe 2 x 14's or two 2 x 12's side by side ... or ????

I can't seem to find a calculator online that will let me try this. The charts only have a single 2 x 12

Any suggestions?

Thanks .... Mike

 

Joists are not normally calculated by doubling them up. It is usually done and tables are available for closer joist spacing. You'll find charts for beams spaced 12", 16", 19.2", 24" and sometimes 32 or 36". You didn't say what joist spacing you were calculating but try looking at closer spacings.

I don't think you'll find a wood product that can carry a heavy load (more than 40 lb/ft) that is only 12 or 14" high and spans the whole distance but you might. You'll just have to look at the charts depending on the amount of weight you want to hold up there. Height is what get the most bang for the buck when spanning long distances and carrying a heavy load. If you must stick with 12 or 14" joists you probably need to consider steel or adding a beam to break up the span.

 

I have the TJI software ... they say a 16" 360 or two 12" 230's (their software gives the choose of 1, 2 or 3 side by side) will work. I know I can get a truss designed and built. I just wanted to check if dimensional lumber will work.

Then I can compare the cost of each option.

Thanks .... Mike

 

Span tables will help with dimensional numbers under normal situations which means single member joists. As you've found most span tables don't cover double or tripled joists. You might gain some insight by looking at the tables for beams but since what you are wanting to do is not standard I don't know if you will find exactly what you are looking for. Your in "engineering" territory. But if you look at the span tables for dimensional lumber with say 12" joist spacing you'll get some idea if your 21'6" span has a snowball's chance. From my quick look 2x14's are a possibility but I wouldn't trust the tables without coming up with some numbers for the weight you want to store up there.