I just had a customer call me with a question I couldn’t answer.
He has a metal roof on a building. On to of the roof they’re putting on 4″ foam insulation backed with OSB. The roof is a 6/12 hip.
His question is – What’s the bevel angle he needs to set his saw to in order to make the bevels fit up tight over the hip ridge?
I’ve never had to bevel anything like that, so I have no clue what the formula is to do a bevel like that. Can anybody help us out?
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Replies
Boss,
The saw setting is 18.43°.
This is a BEVEL angle I'm looking for - Not the plumb cut of a rafter or top chord.
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Boss,18.43° is the bevel angle you need. 19.47° is the hip plumbcut angle for a 6/12. Trust me..... ;-)Joe Carola
It's not that I don't trust you - It just doesn't sound right. How did you come up with that number?
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Boss,The formula is for the Backing Bevel is.Tan-¹(Sine of Hip Angle)Joe Carola
O.K. - I'm not a math genius.How do you do that on a construction master?I don't know what Tan-¹ means...
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>> How do you do that on a construction master? <<6/16.97 = [Conv] [Tan] = 19.47°[Sine] [Conv [Tan] = 18.43°Or.6 [Inch] [Pitch] 6[Inch] [Run] [Hip/Val] [Sine] [Conv] [Tan] = 18.43°Joe Carola
O.K. - I think I get it now.Thanks fer the help.
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Boss,When a hip runs at 45° off the corner and let's say that your using a 2x for a hip, that means that you will have a 3/4" run that sticks off the outside corner of the building. If you take the 3/4" run coming in level, and mark a hip angle plumbcut and draw that little triangle.After that you square down from the top of the hip to where the triangle meets at 90° and that measurement is the rise and the 3/4" is the run and that will give you your bevel angle.Some people think that the backing bevel angle is the same as the hip plumbcut angle and it's not. It's slight less. You will see in the drawing how the small plumbcut hip angle measurement is a little bigger than the the line draw square off the top of the hip. That's the correct bevel angle.There are a few books that say that the hip backing bevel is the same as the hip plumbcut, such a "The Roof Framing" by Marshall Gross and also John Caroll's book says the same thing.Here's a drawing I did some time ago using a 8/12 pitch. I hope it helps a little.The key thing is that the hip backing bevel is measure SQUARE off the top of the hip and not PLUMB off the top of the hip.Joe Carola
"Framer gave you the right bevel angle (18.43495°). It's the same angle you would see if you view a backed Hip rafter in section.
The angle measured on the sheathing or insulation is 48.18969°; this creates a miter line.
To lay this out, take your insulation width and multiply by .89443. For example, if the insulation is 4 feet wide:
48" × .89443 = 42.9325" or 42 15/16"
EDIT: The drawing assumes the long sides of the insulation follow the eave lines."
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Try again ...
Joe Bartok
Boss,Joe gave you the right numbers.
http://www.josephfusco.org/Tips/tip0011.htmlhttp://joes-stuff1960.blogspot.com/
Hey Joe - Didn't think about checking your website.Thanks for posting.
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Boss,If you want the measurement coming in from the corner of the 4' wide sheathing, you can do this with a Construction Master.6 [Inch] [Pitch]48 [Inch] [Diagonal][Run] = 42-15/16"Joe Carola
Framer gave you the right bevel angle (18.43495°). It's the same angle you would see if you view a backed Hip rafter in section.
The angle measured on the sheathing or insulation is 48.18969°; this creates a miter line.
To lay this out, take your insulation width and multiply by .89443. For example, if the insulation is 4 feet wide:
48" × .89443 = 42.9325" or 42 15/16"
EDIT: The drawing assumes the long sides of the insulation follow the eave lines.
Joe Bartok
Edited 5/31/2007 11:45 am ET by JoeBartok
8 min.
That's pretty darn quick, Joe.
I'm still wondering how to calculate it. :)
I have a chart that converts angle to roof pitch.
It says 6-12 pitch roof has an angle of 26.5 degrees.
^^^^^^
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