Help me find the rafter length

[collegecm1]

I have a small project to do and part of it is to determine the rafter length on a 2 houses. 1 is 16'x16' with a 4/12 and a 1' overhang. the other is 24'x30' with a 5/12 and a 2' overhang. If you could tell me how to find this or how to use the calculator on this site it would be appreciated. thanks

[Rich]

For the calculator on this site you would input 4 for the pitch, the ridgebeam width would be 1.5 and the width would be 8 for half the distance of the span, and input 1 for the overhang distance. Rafter length is 9.421' or 9'-5 1/2" from edge of ridgebeam to end of rafter along the top of the rafter.
The actual formula for common rafters is
Square root of (((rise/run) squared)+1)
For hip rafters it's
Square root of (((rise/run) squared)+2)

[Rich]

Another point I should make when using the formula outright - it doesn't account for the ridgebeam width - you need to subtract half the ridgebeam width from your plan distance plus your overhang. So for a 10' span from outside of wall to center of building with a 1' overhang your plan distance would be 10'-11 1/4". Essentially subtracting 3/4" (half the ridgebeam) from the plan distance.
Hope that helps.

Or you could grab a framing square and actually lay it out.. may not be as accurate but once you're able to do it it's simple. :)

[grumpydasmurf]

Rich you may be figuring the rafter length like a carpenter, not a roofer. If he's figuring the ridge length for roofing purposes a few inches doesnt hurt anything. Now if he's figuring the rafter for carpentry purposes, a few inches is a big mistake.

If for roofing purposes here is how I do it:

I take the length from gutter to ridge, ground measured. In this case it's 16 from gutter to gutter on the 4/12. 8' x 1.05 = rafter length.

On the 5/12 I will assume 24 is gutter to gutter, so I take 12' x 1.08 = rafter length.

You will find this is accurate to within a few inches... which is all it needs to be if figuring roofing squares. If your framing use Rich's calculator.

[Rich]

That's exactly what my formula does.. 5/12 comes out at 1.083. It's also the same formula that my Roof Area calculator uses. :)

[grumpydasmurf]

I know but you were talking about swubtracting for ridge beam width etc... So I was pointing out you *might* be over complicating things... but maybe not. In which case I'm just wasting finger muscle.

[Rich]

LOL.. ic. Not wasting... building.

[grumpydasmurf]

Yeah I can have big ol didgets like Arnold!

I'm going to Flip you off!

[Rich]

LMAO