OT Max rafter length

We get heavy snow loads where I live and 60 lbs. per square foot is the minimum code requirement for most buildings. For a 15' span, if you are using common spruce lumber, 2 X 12s will just barely make code if used on 16" centers.

The strongest wood, e.g. Douglas Fir, Southern Yellow Pine, can carry a longer span than weaker wood - e.g. spruce, white pine, red pine, hemlock, etc. In my area - all standard framing lumber comes as spruce - but I am in New York. If I buy rough lumber from a local mill it will be hemlock. If I lived down south - the wood would likely be much stronger as Southern Yellow Pine.

30 lbs. snow load - 16' span - 24" on center - 16 feet max. span - 2 X 10 best wood. If spruce, only 14 feet.

40 lbs. snow load - 14 1/2 foot span max. - 24" on center - 2 x 10 for best wood, 13' for Spruce.

I've built several buildings over the years with 20 foot spans using 2 x 12s on 14" centers. That meets the new code regs. and will hold a lot of snow in case I'm not around to shovel it off right away. It's not an issue with most of my 5/12 roofs with steel - but flatter roofs can be a problem. Technically, a 2 x 12 of the strongest wood is rated for a 17 foot span at 60 lbs. of used on 16" centers, and 14 1/2 foot on 24" centers.

I have 5 acres of Douglas Fir you are welcome to come cut a few for personal use. I think its about $1500 per 1000 right now. Boy I remember when my uncle complained when finished lumber went from $50 to $55 per 1000.
Walt

Whatever it is - my local lumber years won't special order it anymore - too expensive, I guess.
Been that way for 15 years at least.

On the subject of wood and where it comes from - believe it or not, I just bought a bunch for framing lumber and all the 24 foot 2X4s are from Russia! What the heck sense does that make? I can understand with certain exotic hardwoods - but spruce framing lumber?

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