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Metal roofing, valley angle cut

Stikineriver's picture

Hi all. I just started installing sheet metal roofing (Skyline 16'' wide) on a house which has 2 gable dormers. I snapped my line in the valley, 4'' out of center and made a jig to clamp to the metal and used a metal stud saw blade to cut a clean line. The problem was figuring out what the angle was. Now I know there are many smart builders who must have figured out a trick to this. My main roof & dormers are 6/12 pitch. Any ideas?

(post #101506, reply #1 of 5)

I don't figure the angle, because it can change if the valley is not perfectly straight or if there is a dip or crown in the valley.

Measure a right triangle from the center of the valley at the bottom straight up to the ridge and over to the center of the valley at the top. From your horizontal measurement (ridge), determine how many rows you will have (say 5.6 rows). Divide your verticle measurement by that number (120" / 5.6 rows = 21.43"). Each row will be 21.43" shorter than the preceeding one. Measure up which ever side of the pan will be shorter and mark a line between it and the bottom on the other side. Make the cut. If you're just overlapping the valley, that should be close enough. If you're locking to the valley, you might need to tune the angle slightly with your fold.

 


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(post #101506, reply #2 of 5)

The blade bevel along the Valley trough line for two 6/12 pitches intersecting at 90° in plan is 18.43495°.


If the sheeting follows the ridge lines the angle on the material is 48.18969°. If it follows the lines of the gable ends (the same as rafters) the angle on the material is 41.81031° ... this is the jack rafter side cut angle and may be found on the tables on the framing square.


Joe Bartok
Joe Bartok

(post #101506, reply #3 of 5)

I don't agree Joe.  The first number should be 18.434947.  And the other numbers are off a similar amount.   After all, this is Fine Homebuilding, not Adequate Homebuilding.  Shame on you.


 


 


"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

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"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it."  T. Roosevelt

(post #101506, reply #4 of 5)

Rats! Got caught with my pants around my ankles on that. How will I ever live this down???


I should have given the backing bevel as 4/12 ... now that's EXACT.


Joe Bartok
Joe Bartok

(post #101506, reply #5 of 5)

I'll forgive you.

But I chalk it out and measure the actual like CU

 

 


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