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Discussion Starter · #1 ·
I've been meaning to get back to my study of sloping ridges and after I recieved a private message this morning about Gable Walls Non-Perpendicular to Ridge it seemed like a good time to start a new thread on this subject.

In the attached drawing I've drawn out a gable roof with a ridge that is not perpendicular to the gable end rafters. The way I see it, the ridge has to be a sloping ridge for the roof sheathing to work. So the first thing we need to know about Gable Walls Non-Perpendicular to Ridge is the drawing relative to the private message?

Sim

Note: I lost my password. Used the send password send button about 20 times and never received my password to login. So I used a different email address to sign up, but was banned immediately from contractorstalk for ever. So, this morning I signed up again with a different email address.

If I don't post again here at contractorstalk.com, I've probably been banned again.
 

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Discussion Starter · #3 · (Edited)
Is this a general discussion, or is there a specific question(s)?
Both, general discussion and

Gable Walls Non-Perpendicular to the Ridge

is the ridge level or sloping?

Also, the sloping ridge on the dormer is probably the one of the hardest roofs to draw out geometrically for the cut lengths or using trigonometry to find the roof framing angles for.

Sim
 

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Discussion Starter · #9 ·
I looked in my German Roof Framing Books, none of them have the roof layout that Fuller Framer is faced with.

Basiswissen Dachausmittlung has a drawing with the plate lines not parallel , but the ridge is still sloping.


While FullerFramer is scratching his head on his roof...

I was discussing this roof with Brent Green. The roof has level plate lines that are parallel and a sloping ridge.

Wharton Esherick Museum

http://www.tripadvisor.com/Attracti...arton_Esherick_Museum-Paoli_Pennsylvania.html

Sim
 

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KemoSabe
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I'm not sure why a sloping ridge would be treated any differently than a bastard hip or valley unless it runs parallel to the plateline. In the drawings above, it does not. Treat as a bastard hip.

If it is parallel, with a level plateline and a sloping ridge, it's no more complicated than knowing the run and rise of the ridge and breaking it down to a common rise/rafter spacing. Use the common difference to calculate each rafter length and pitch individually because the run is a constant and the rise will change incrementally. No need to overcomplicate it by overthinking/over-mathing it. It will end up with a twist due to the constant pitch change.
 

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KemoSabe
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Just to mention, in my current situation the ridge is not sloping and the pitch is a constant 12/12.
I guess I'm missing some information as to what the question is then. Fill me in on the details so I can learn something.
 

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Discussion Starter · #17 ·
I wasn't interpreting the question or plans correctly. The roof for Fuller Framer is a prow roof with plate lines that are not parallel.

For the hip rafter slope angle on the you can use :

With a plan angle of 62.06°, common rafter run of 120" with a 12:12 pitch roof.

Hip Rafter Slope Angle = arctan (tan Common Rafter Pitch Angle × sin Plan Angle)

Hip Rafter Slope Angle = arctan (tan 45 × sin 62.06) = 41.45862°

Roof Sheathing Angle = arctan (tan Plan Angle ÷ cos Common Rafter Slope Angle)
Roof Sheathing Angle = arctan (tan 62.06 ÷ cos 45) = 69.44264°

120" x tan( 62.06°) = 63.44"

Hip Rafter Length = 63.44" ÷ cos (69.44264°) = 181.24718"
Jack Rafter Length Difference = spacing x tan(Roof Sheathing Angle)
Jack Rafter Length Difference = 24" x tan(69.44264°) = 63.99555"

Here's a link to more examples of using the roof sheathing angle to calculate rafter lengths.

http://sbebuilders.blogspot.com/2013/09/hip-valley-roof-framing-example-1.html


Sim
 

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Discussion Starter · #18 ·
Getting back to my study of sloping ridges.

In this drawing the eave angles are A & B = 77.66091° and C & D = 102.33909°. The ground plan has two roof slopes that are 35° & 55° and the ridge is sloping and not parallel to any of the eave lines. In this drawing I'm using the average rise of 2.1422cm in each profile view of the roof slope triangles that are perpendicular to the eave line to establish the averaging lines, that develop the averaging intersecting points that define the hip rafter run lines in plan view. When the roof pitch is equal on each side of the hip rafter the eave angle is bisected to form to equal plan angles.

Links to
Base Knowledge of Roof Surface Averaging
from the book Basiswissen Dachausmittlung

http://sbebuilders.blogspot.com/2013/10/basiswissen-dachausmittlung-3-averaging.html

http://sbebuilders.blogspot.com/2013/10/basiswissen-dachausmittlung-2.html

http://sbebuilders.blogspot.com/2013/10/basiswissen-dachausmittlung.html


Sim
 

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Discussion Starter · #20 ·
Here's some more drawings of the geometric development of the sloping ridge that's not parallel to the eave lines.

Using trigonometry for the king common runs.

Plan Angles
A = 77.66091 ÷ 2 = 38.83046°

RafterTools
77.66091° Eave Angle
Plan Angles
23.43872° & 54.22219°


Plan Angles
C = 102.33909° ÷ 2 = 51.16954°

RafterTools
102.33909° Eave Angle
Plan Angles
74.19138° & 28.14771°

Law of Sines for the king common rafter runs.
a = ( c × sin( A) ) ÷ sin( C)
a = 3.1457 = ( 7 × sin(23.43897) ) ÷ sin( 117.73058)
b = ( c × sin( B) ) ÷ sin( C)
b = 4.9586 = ( 7 × sin(38.83046) ) ÷ sin( 117.73058)
h = a × sin( B )
King Common Run = 1.9724 = 3.1457 × sin( 38.83046 )

For the angle of the sloping ridge ???
Why too much trigonometry, it's easier to use geometry to calculate the angle of the sloping ridge.
 

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