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Forum topic by tigger959 posted 07-05-2011 06:20 PM 925 views 0 times favorited 6 replies Add to Favorites Watch
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tigger959

50 posts in 3190 days


07-05-2011 06:20 PM

Will be building a pole barn and the dimensions are 12’W x 8’D x 8’H. The poles at the rear of the barn will be 8’ tall. Since I want to put a slant roof (From Rear to Front), need help in determining what height the front poles will be. Am thinking of putting a 15 degree slant.

-- Tigger, Texas


6 replies so far

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nailbanger2

1041 posts in 2605 days


#1 posted 07-05-2011 07:13 PM

Tigger, to start with, a roof’s slope is stated as a rise/run number. I don’t have any tools to determine what a 15 degree pitch would be, but to illustrate let’s use 45 degrees. When you are laying a 45 degree line out, you start with two perpendicular lines that disect each other. These make 4 quadrants. In one quadrant you mark 12” on each line, the horizontal one could be called the run with the vertical one called the rise. That would be called a 12/12 pitch.

Going totally by memory, I think a 3/12 pitch is what you’re looking for. It’s OK if it’s not, adjust it accordingly. For a 3/12 roof with your measurements, the front pole would be 8×3=24, or 24” shorter than the rear poles.

Let me know it that makes sense or not.

-- Wish I were Norm's Nephew

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scrabby

42 posts in 2647 days


#2 posted 07-05-2011 07:31 PM

Banger is correct…a 3/12 pitch equates to 14 degrees. Assuming the poles are 8’ apart, the front poles should be 2’ shorter.

-- Jim, North Vancouver, BC

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tigger959

50 posts in 3190 days


#3 posted 07-06-2011 01:04 AM

First off, want to thank you all for your help. Now, let me admit my ignorance by asking how one determines the degrees from the pitch or vise versa. Also, after reading your responses, 15 degrees seems way to much of a pitch for 8’. What are your thoughts?

-- Tigger, Texas

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nailbanger2

1041 posts in 2605 days


#4 posted 07-06-2011 09:21 AM

Get yourself a Swanson speed square. These handy little tools are cheap and irreplaceable when it comes to framing roofs. Make sure you get one that has the little blue book in the package. The book is how I learned to frame roofs thirty years ago, and they haven’t changed AFAIK. When you get the square, you’ll see it has all kinds of markings on it in different spots. You put the pivot point on a rafter and turn the square to , say, 3, and in line with the edge of the board will be the corresponding angle. Here I am typing in the dark when I forget about the internet. This guy does the typing for me.

http://zo-d.com/stuff/how-do-i/how-to-use-the-swanson-speed-square-as-a-framing-square.html

And a fifteen degree is about as low as you would want to go for the pitch.

-- Wish I were Norm's Nephew

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scrabby

42 posts in 2647 days


#5 posted 07-07-2011 02:02 AM

It’s not really important to know the degrees, unless you’re particularly mathematically inclined towards degrees.

Having said that, if you remember high school trigonometry, use this formula in Excel or a calculator to go back and forth between pitch and degrees:

To get degrees: Tan^(-1)(rise/run) = degrees, where Tan^-1 is also known as Arctangent or Inverse Tangent

To get ratio of pitch: Tan(degrees) = pitch ratio

Examples: Tan^-1(3/12) = 14.03 degrees or Tan(15 Degrees) = 0.268 or about 1/4, same as 3/12

Better yet, use the speed square and avoid the trig.

-- Jim, North Vancouver, BC

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tigger959

50 posts in 3190 days


#6 posted 07-07-2011 03:05 AM

Thanks a lot to all of you. After speaking w/some local woodworkers, I decided to just drop 6” from the back to the front. I almost got a headache trying to figure things out. Guess I think too much!

-- Tigger, Texas

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