# calculating slope for patio cover



## 12penny (Nov 21, 2008)

ep...welcome. I assume you want you want to know the angle to cut the rafters where they meet your ledger board? I come up with about 87 deg. Cant be exact because I'm not there. Cut it at 87 and then put it up and check it. If its off, scribe it and recut. Good luck.


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## epdave (Jan 7, 2009)

*slope*

Thanks Penny. how did you get to this figure.

dave


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## 12penny (Nov 21, 2008)

Drew it on Deltacad and measured the angle. My calculator's in the truck and its raining outside. I cant imagine anybody could explain how to figure it in a forum. Go to your local lumber yard and ask for a ConstructionMaster calculator. Does everything from rafters to stairs. Good luck!


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## epdave (Jan 7, 2009)

*slope*

did you mean .87 or 8.7, 87 degrees sounds a bit much?


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## 12penny (Nov 21, 2008)

I guess its all in how you look at it. I should probably have answered 3 deg. Put your speed square on your rafter. Pivot speed square to 3 degrees and draw your line. I may have been confusing, sorry. Make sure your crowns are up and scribe if you have to.


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## Bob Mariani (Dec 1, 2008)

Break it up into a right triangle. so if the height is 8'3/4" - 7'3' The leg of the triangle is (a) 1'3/4" The base of your triangle is 9 the angled side (hypotenuse) is 13'6" So the arcsine (header down) is 83.22 degrees. The angle above your post is 6.78 degrees. 
Or you can think of this as a simple stair rise. The 1'3/4 is the rise 9 foot the run


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## Jack of most (Jan 21, 2009)

Slope equals rise over run. Run is half your span. Span is the total width of the house. Rise is the total height of the roof from the top of the wall framing. So that means that... Span x .5 = Run. Rise divided by run = slope. I think I remembered that right.

There is 180 deg. in a right triangle. So if you have the figures for two of the angles the third should be the remainder out of 180.
A squared + B squared = C squared


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