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epdave 01-07-2009 01:42 PM

calculating slope for patio cover
I am in the process of of DIY Patio Cover. I got the main support attached to the house and ready to start putting on the four support beams but have to calculate the slope. Can someone explain a way to do this in easy DIY terms.

Here is what i got.

I have the main 2" x 6" x 16' beam attached to the house 8' - 3 1/4" high flush right under the soffit. The beam is actually 5 3/4" not 6"

The support beams 2 x 6, will extend out 9' and rest on the support post that are 7' - 3" high.

What would be the slope? How do i get this figure?

Geometry Challenged.


12penny 01-07-2009 02:12 PM

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.

epdave 01-07-2009 04:48 PM

Thanks Penny. how did you get to this figure.


12penny 01-07-2009 07:37 PM

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!

epdave 01-08-2009 09:42 PM

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

12penny 01-09-2009 07:14 AM

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.

Bob Mariani 01-09-2009 02:03 PM

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

Jack of most 01-21-2009 10:22 AM

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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