How to back into Max Live load?

[andrew978]

Last year we had 5' of snow on our roofs so when designing my shed, I upgraded the rafters.

At some point I will get a PE stamp but I'm curious if I could at least get a ball park for now on what snow depth my roof can hold?

All the calculators online give you the max span. I guess as long as you are under that you are fine. I'd like to input my variables and instead of max span, have the calculator tell me what live load I can support.

Anyone know how to "plug" for live load if the following is known:

Horizontal span : 7'
Member Type: Rafter (snow load)
Deflection limit: L/360
Spacing: 16
Snow Load: n lbs/ft
Dead Load: 20
Wet Service conditions: No
Ground Snow Load = 50 psf (Portland ME)
Thermal Factor = 1.2
Roof Type: Gable
Pitch : 12/12
Exposure: Full
Rafter : 2x10
Spacing : 16" OC

 

[kaymccampbell]

How about upping your load variable until the calculated max span equals your real span?

 

[Homerr]

Need to know what type of wood your rafters are.

 

[matt_i]

It is just a 7 foot wide span? That's like a garden shed...

 

[JCByrd24]

Assuming #2 SPF in Maine.

I can't help directly convert depth to psf but if you are doing what those inputs suggest you don't need to worry about snow and you are way overbuilding. Doing as suggested above and just upping the number in the AWC calc I'm seeing over 200lb/ft^2 live load, just crazy. Even on a flat roof snow won't accumulate like that in Maine. On a 12:12 pitch you will never get that much snow. 2x10s are routinely used in Maine for twice that span (28' wide buildings) on a 12 pitch

I'm building a chicken coop right now with a 4 pitch and I'm using 2x4s 16"OC for a 6' span shed roof. I just ran the calc (didn't before I chose 2x4, it's a chicken coop) but it'll support my span for 50psf, should work fine.

I'm a PE in Maine.

 

[andrew978]

Hey thanks for the replies. Yeah the "garden shed" is 14' wide, but the span is 7'. And yes, I'm totally overbuilding it in part because the neighbors shed last year collapsed from the snow and the shed is directly in the path of a major wind channel in our area and we see 40-50mph gusts over there.

I like the idea of being able to plug the variables separately "upping your load variable until the calculated max span equals your real span" Issue is I can't find a calculator that lets you do that online. I bet there is software out there but I can't find anything.

And JCB thank you for the rough calculation. 2x10's in Maine for a 14' run? Thats insane but makes me feel great. I came close using some hard math and I'm around 240lb/ft^2 live load. WOW!

This is why I'm not a builder. I'd end up overbuilding everything and never make any money.

 

[JCByrd24]

Google "AWC span calculator" to find the calculator I used. If you have a lot of wind and are really concerned, pay attention to joining the roof to the walls properly and then anchoring the whole business to the ground.

 

[jim whitney]

2x10s ,16oc 14' span overall, 12/12 pitch ,Jesus you could put a Mack truck full of snow up there!