Teardrops n Tiny Travel Trailers

I'm designing a standy that is 7' wide outside to outside. Plywood walls.

I live in canada and it will be stored outside, building code snow loads in my area are 56 psf. What should I be using for ribs spanning that gap? I worry that 2x2s will be too weak, particularly because I have a 4'8" long flat section on the roof.

So to sum up, what ribs material and size, and also spacing between ribs, particularly at the top.

I'd like to keep my roof thickness to a minimum, 3" max if I can.

Thinking that with 2 1/2" deep rafters, 12" on center you should be ok. 56 psf is a lot of snow load! You must be in the mountains somewhere to get that much accumulation. I would use 1X3 material to keep the weight down as much as possible & find some with some "crown" up a bit, maybe 1/4" across the 7' dimension. With an outer & inner skin, glue, foam insulation & proper joints it should be fine that way.

Sorry if I'm not up on your codes, I did roof trusses for a living but it was here in Tucson, so we didn't get that much snow to deal with...

I don't know how much of your roof will be flat, other than the 4'8" section mentioned, or how much support your standing walls can add to the equation, but in another thread about a flat roof sagging query, I linked-in a tool I used before I built my flat-roofed squareback 4x8 TTT. http://www.tnttt.com/viewtopic.php?f=2&t=70642&hilit=+sagulator#p1233403 The Sagulator could answer your questions about acceptable loading, especially if you choose to build with a totally flat roof, and just a few, or no spars underneath. Anything's possible if you can ask the right questions, and are willing to find the right answers...whether they follow the normal pattern or not. I was advised to put at least three spars under my flat roof, but didn't, after calculating the loading, and it still remains flat today.

Based on the sagulator, I think I would need to do 2x3s with 12" on center. Something to think about.

I wonder if I curve the roof up in the middle a bit whether that would make a big difference.

My reply was based on a system which has a 2 1/2" deep rafter, 12" centers & the top & bottom skin attached with nails or screws & glue. The camber of 1/4" should help with deflection when a load is applied. The rafters won't take the load without a skin top & bottom. Take a look at the large trailers on the highway which are empty. Usually, you will see they have some camber on the upper side, which flattens out with the load.

Thanks. I had been thinking a small camber would be helpful to hold up under heavy loads.