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Small Cabin Forum / Cabin Construction / help me out with roofing math/pitch
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trooper dan
# Posted: 11 Jan 2010 19:18

Ok, I need help figuring out how much material I need for a steel Gable roof using 8' sheets with a 1 ft over hang on each side. (roof trusses will be 2x4s on 16" centers.

What would be my pitch and dimensions for roof trusses? The building is 12x14 (design changes from the previous 10x15) I am not really good with math equations.

Thank you in advance!

# Posted: 13 Jan 2010 10:41

When I bought my tool for measuring angles and cuts (triangle in shape) a small book came with it. It easily details rise and run and how to determine pitch as well as rafter notches or cuts. A google search would do the same.

If you are in a winter zone a higher pitch for snow loads is beneficial.

# Posted: 19 Aug 2010 23:18

5/12 would work fine the equation is A times A + b times B = c times c
if you are twelve foot wide and you want a regular gable meaning the ridge is centered unlike a salt box style gable roof where the ridge is off center you simply take your c times c which you've said is 8 foot im gonna assume you don't want to add a 1 foot ripper at the top or bottom of your run for your overhang so we're gonna subtract that foot before we square so the over hang works out 7x7 equates to 49 then you would subtract one the distance from your outside wall to the center squared in your case you have a twelve foot endwall to the center would be 6, so 6x6 =36 a(a)+36=49, 49-36 =13 find the square root which is 3 foot seven inches roughly

then to get your pitch figure 3.6(12) divide by 6 should work out to 7 over twelve ish. 30 degrees rough. you can get more eave if you squash it to 4/12 18.5 degrees rough that is as low as I would go with a metal roof unless you're in a southern climate where ice damming isn't an issue and you don't have any dormers. I think you can go as low as a 2l12 with the metal if you use Ice and water shield and shrink the exposure with more lap but it's taking more of a risk. hope this helps roofing can be tricky but you'll be fine get the walls up post up in the middle for the ridge and screw a rafter at the end wall to hold it in place while you scribe the angle at the ridge and crows foot. then cut it check it on both sides at both ends and in the middle if everything is square and straight it should work perfect in all six locations. mark p on that rafter and use it to trace all your rafters. cut six first, fit and screw them into place on the ends and in the middle if everything checks cut the rest and fill them in make sure you're braced off well and you crown your rafters so high is up. get the plywood on asap to rack it all together and you're done good luck a 7/12 can be tough to walk but it can be done 2x4 scraps screwed into the plywood will help while you're putting the metal on.

# Posted: 19 Aug 2010 23:21

Quoting: sam
crows foot.

I meant birds mouth

Gary O
# Posted: 20 Aug 2010 21:56

Trooper Dan-
If you're like me, after reading much, and getting well meaning, well thought out direction, you ended up frowning, scratching your head, and heading to the fridge for a mind soothing brew.
Go to:
or google:
'rise run'
All you have to do is enter either rise and run, or anlge and run, or any combo of two out of the three and it'll give you the third.
It's a trig function, and I'm of pre-algebraic descent...........

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