supporting a tin roof shed advice needed

[kossetx]

I have a garage with a galvanized tin roof. I'd like to extend the back of it so I would have a covered work/carport area. I have some 21' galvalume that I can put on it and the garage is 24' wide. I would like to have poles only at the corners of the roof, if possible. What is the best way to support a roof like this. I'm thinking 2X6's would bend/warp over a 20' span. Extra poles across the 24' span is no problem but I would like to keep the 21' sides open. Any thoughts? Thanks, Mark

 

[jinman]

If you want to keep the sides claer and only put up two corner posts, I think you may have to go to 2x10s. I have a 24x24 building that is freespan under 2x10s set on 4' centers, but the tin runs across the beams rather than along their length. Since you are running your metal lengthwise, you'll have to put in furring across the beams. I think you may even be able to get away with 2x8s if you set them on 2' centers, but I don't think 2x6s will span 20' without some sagging. I would not run them anymore than 12' to 16' on a carport type roof without a crossbeam in the middle.

 

[EddieWalker]

A good way to get extra strength out of lumber on long spans in to sandwich half inch plywood between two boards. Then glue with liquid nails and screw them together. I'm not sure on sizing, but you can google that and find a chart for the type of wood and distance of your span.

Eddie

 

[jinman]

Eddie, that's a good idea about googling for the answer. I took your advice and here are three tables I found for ceiling joist spans. On a low-pitch roof without bracing, the carport most closely represents the ceiling joist load rather than the rafters. All these tables have slight variation.

First Link
2nd Link
3rd link

 

[schmism]

10psf LL is really not useable....

18 psf is about as small as you get even for sunshine states.