Lean-to snow load

[mjr5253]

I am building a 30 x40 x10 garage this summer. It will be all stick framed, 16" centers, 2x6 walls, etc.
I am looking to build a lean-to off the entire back side (off the eave end of the building). It will come off the building 14' and be 40' long. The garage roof will be a 6/12 pitch and I will tie the lean-to roof into the garage roof with a pitch change. The issue I am seeing is that if I start the lean-to on the building side at 10' tall, I can only have a 3/12 pitch if I want to maintain 6' 6" clearance on the low end (trying to avoid the lean-to concrete being lower than the garage floor concrete if possible). I live in Northeast PA just north of Scranton. We get a decent amount of snow. I am wondering if I should be worried about snow load. I would put the rafters 16" on center, and use 5/8 plywood for sheathing (both the garage and the lean-to will be shingles, NOT steel). I'll use 6x6 posts on their own footers for the low end. I was thinking I'd use 2x8's for the rafters. Maybe 2x10's would be better? Is this too shallow of a pitch?
Any input would be appreciated

Thanks

 

[jack stand]

I just built one exactly the same size, in Maine. I did use a metal roof on the whole building that's also a 3/12.
You mention that it's on the "back" meaning out of sight (I guess) 2 advantages in your situation is its much lighter (dead load) and the snow will slide off.
I sawed my own lumber from my own trees so I made the rafters 2x10 (full dimension), also on 16" centers. The roof metal is 16' long providing a little overhang and +/- 14' inside the posts. Just to be safe I'd suggest a 2x10 also, but for sure with a shingle roof.

 

[billconner]

In some buildings when you have a lower roof like that, there is increased snow load from drifting. Our attached garage is like that with trusses on 12" centers.

 

[chad215]

Like Bill said- snow drift is a concern. This can multiply the loads compared to a stand alone structure, as well as adding additional strain to the existing building.
Sorry-don't have a better answer than that, but you need to be aware of this.

 

[Prospecter]

Pretty sure asphalt shingles need at least 4/12 pitch.

 

[billconner]

Pretty sure asphalt shingles need at least 4/12 pitch.

I think they can be 2/12 with continuous ice and water shield under it.

 

[Prospecter]

Good to know. Thanks.

 

[BDT/NWMN]

Being You are building a completely new structure, I would recommend considering going 30' X60' and skip the added lean-to