Replies

1. 
   DoRight | May 05, 2012 04:20pm | #1

   Well, you CAN.

   But should you?

   20 feet is a long span.  With metal roofing to shed the snow I would guess, and I say guess if you are interested in guesses, you would be ok.  However, a 4 in 12 pitch in my experience does not always allow snow to slid (5 in 12 always slids, my experience). 

   All that said, load tables should not be hard to mind and your lumber yard will probably tell you all you need to know.

1. 
   t25iger | May 06, 2012 01:06am | #3

   Thank's after consuting alot of profesionals , I think I will stay with my original plan and go 2 feet apart. I think this is over kill , but with the lake effect we get I would rather be safe.

2. 
   Piffin | May 05, 2012 08:22pm | #2

   Check span tables

   I can only guess at the required live load for roofs in your area. You need to find that out first, then just go to the yard where you will but the I-joists. Any retailer of this product has the software to calculate the layout for you. I suspect you are looking at 19.2" or 24" layout, but there are three different I-joists with different sized cchords and thicxknesses of center web.

   My concern would be what sort of ridge beam you plan to use and how you will attach these rafters to it

1. 
   t25iger | May 06, 2012 01:11am | #4

   This will be a addition to another structure. I will be attaching to a 2x12 with a joist hanger. The other end will be attached to 2  2x12's at the rake edge with 6x6 5 feet in the ground.