How low does your lean to go?

[Cord]

You'll also have to consider "drift" because of the valley.

 

[the old grind]

'Inverted trusses' to re-pitch that whole side of the barn to 4:12? See how high your eave would be 12' out with the low chord (lean-to) horizontal ...

Trusses 4' OC and 2x4 24" across them are common under ply decking at 4:12 pitch here near the 43dr parallel, and easily makes snow load reqs. RH wall of barn can carry that, no?

Is the ground sloping away to the right as it appears to be? Put a gardrail on the right side of the entry slab and carve/grade another 6" of clearance there? Concrete is wonderful. Gravel is fungible. (I now return to 'the box') t o g

 

[bcp]

I would stand up a vertical 2x4 with braces on the barn wall and and a taller one where the new wall will be. C-clamp a "trial "rafter" and try different positions for size.

Bruce

 

[Rustyiron]

It's a bit more work, but you could have both, a decent width lean to (with head room) and a good roof pitch if you put your shed rafters up somewhere (about) above your window on the existing roof. You'd have to cut the metal and build a small support wall on top of your existing side wall to carry the new rafters.

 

[fried1765]

Snow won't shed much if you go below 4:12. It'll just melt in place. That's where your could get a little daming and leakage from the seams and slope transition. I know you can go all the way down to 1:12 and have it shed water, but I wouldn't recommend going below 3:12. Even then, I'd use butyl tape on the lap seams to make sure it doesn't leak. Depending on how much drift you get in the valley, you might want to tape up the existing seams as well. I'm only saying this because I see you are in a heavy snow climate. If this was a southern climate I wouldn't be concerned.



Per the picture, I don't think there is enough eave height to use a single pitch truss. I'd stick frame it with some 2x4 purlins @ 24"o/c

That is exactly why I too suggested 4/12 in my earlier response ("resident CE")

 

[s219]

I went 3:12 on my lean-to because it was the only way I could get decent clearance underneath to drive my RTV in (which was the whole point of the lean-to). DO whatever it takes in terms of framing and roofing materials to maximize clearance while satisfying snow load requirements. This isn't a place to cut corners -- you want that space to be as versatile and useful as possible.

 

[fried1765]

I went 3:12 on my lean-to because it was the only way I could get decent clearance underneath to drive my RTV in (which was the whole point of the lean-to). DO whatever it takes in terms of framing and roofing materials to maximize clearance while satisfying snow load requirements. This isn't a place to cut corners -- you want that space to be as versatile and useful as possible.

SNOW LOAD!
The potential snow load in Virginia is likely way less than Idaho!
3/12 may be fine in VA. ... not very satisfactory in ID.

 

[aczlan]

Snow won't shed much if you go below 4:12. It'll just melt in place. That's where your could get a little daming and leakage from the seams and slope transition. I know you can go all the way down to 1:12 and have it shed water, but I wouldn't recommend going below 3:12. Even then, I'd use butyl tape on the lap seams to make sure it doesn't leak. Depending on how much drift you get in the valley, you might want to tape up the existing seams as well. I'm only saying this because I see you are in a heavy snow climate. If this was a southern climate I wouldn't be concerned.

Per the picture, I don't think there is enough eave height to use a single pitch truss. I'd stick frame it with some 2x4 purlins @ 24"o/c

When they put up our pole barn, they used sheets long enough to go the length of the roof, then they ran a bead of silicone caulk on the down the seam between each sheet.

Aaron Z

 

[s219]

SNOW LOAD!
The potential snow load in Virginia is likely way less than Idaho!
3/12 may be fine in VA. ... not very satisfactory in ID.

A 3:12 should not be an issue even in Idaho. I have a friend out there -- what we call a "lean-to" they call a "shed-off" -- and his hangs off one eave wall of his shop. Can't be more than 3:12 or 4:12, and I've never heard of him having problems with it.

You can design any roof slope for any snow load if you want to, which is what I was conveying to the OP. I have been to ski lodges in Utah with completely flat roofs and 12+ feet of snow sitting on top. It will come down to how stout the rafters or trusses are, the rafter spacing, available/required clearance underneath, and cost, to decide what's feasible.

I can exceed snow load requirements here on a 3:12 over 12' span with 2x8" rafters every 24", which leaves a lot of room to handle increased snow load in other locations through bigger rafters, tighter spacing, etc. Rafter spacing scales the effect linearly, rafter width scales it linearly, but rafter height goes to the third power. As an example, if someone went to a 2x12 rafter spaced 12" on a 3:12, they'd be able to handle over 7X higher snow load than my roof, and that is a dead simple way to do it with easily obtainable building materials. Trusses could be designed to far exceed a 2x12 of one wanted to get a little more sophisticated.