Lean-to Rafter Size

in-too-deep

Well-known Member
Hi folks!

10 ft span
2/12 pitch
24 in. O.C.
1x4 purlins and steel roofing
Northwest Minnesota snow load.

What size boards would you use? 2x8 enough?

Thanks!
 
Sorry, there was supposed to be line breaks in there.

10 ft span 2/12 pitch 24 in o.c. 1x4 purlins with steel roof

NW Minnesota snow load
 
Should be nothing less than 2x6 16 on center. If you go to 2x4 purlins you could probably go to 24 on center for the rafters.
 
I dunno what the roof above it is like, but I would go with 2x4 purlins. I am going to add one and it will be along my 40' wide shed. The snow coming off that in the winter is substantial. Never saw it come off all at once, it slides down the roof like a glacier and keeps dropping off hunks. I assume these would continue off the shed but where it hits now it makes a heckuva pile. :)
 
Agreed. That 2/12 is getting pretty flat. If you can get a couple inches pitch somewhere it will help.
 
You did not mention type of wood or the actual snow-load requirements where you are. In the NY Adirondacks - if you used S-P-F lumber, 2 X 10s would be required for a 60 b. snow-load. If a high-strength wood like southern-yellow pine or douglas-fir, then a 2 X 8 is allowed. No way would I use 1" X anything for purlins.
 
You don't need a really heavy rafters for a lean-to roof 10' wide. As others have noted you do need to address how far the snow has to fall off the barn roof you are attaching the shed too. (IMPACT Load) from barn roof. It makes no difference how big of 2Xs you use for rafters, it is how well they are attached to the main structure.
I have seen decks totally ripped of houses, where the ledger plate was improperly fastened, or joist straps weren't used.
I built this 11x82' lean-to on the north side of my shop 6 years back. As you see, I have no worries about impact loads and this structure recently withstood the 32" snow storm we got without any problems. The ledger plate on the gable end of the shop is thru bolted on the studs with 5/16' redi-rod. The plates are 2x6s, rafters, 2x4s, and furring strips for purlins and left over steel and other salvaged components from building projects when I was a contractor.
It was a cheap build and is serving me well.
Loren
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you need to find out the required snow load---and determine the allowable stress for the type and grade lumber your going to use
 
I agree 100%. With only 10' to span the attachment to the original shed is by far the weakest point.
 
A lot depends on the wood. If you are using whitewood I think I would use 2x10's. If it's southern yellow pine 2x8's should do it.
 
Two examples: The first one, on the house, is a total 12' span. I put it up 32 years ago as a temporary cover for my tractor and boat until I could afford a barn. It was built wit 2x4s on 16" centers. Ten years later, when I decided it would become permanent, I doubled up the 2x4s. It is going on 33 years. The lean to on the big barn was added in 2005. It is 1-12 pitch, 13' span, and I built it with 2x10s on 24" centers. I did have one 2x10 start to sag because of knots, so I doubled it up before I put the metal roof on. So far snow hasn't been a problem in SE MI. If I were in MN, I'm sure I would pay more attention to clearing the snow from them.
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Thank you all for the input! I will use 2x4 purlins instead of 1x4. I will post pictures when I get it done.
 

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