It was in the roof inspection course and now I see it in the National Home Inspector Exam text book.
“Valleys are at a lower slope than the intersecting roof planes”.
How?
If you have a 6/12 meeting a 6/12…. How is it not still 6/12 in the valley? Google is failing me on this too. Is there an explanation or better yet a diagram?
Thanks.
The angle remains the same.
It’s at the bottom of the truss or rafter.
I think I’m understanding what they mean…. If the slope is measured from the dead bottom of the valley, it would be at roughly 45 deg angle from the peak, so less slope.
So measuring along the valley flashing would technically be less slope.
Strange way to word it.
A common rafter travels at 12" and since the valley is at a 45, it travels at 17", so when you have a rafter with a 6/12 the valley rafter would be at 6/17 because it has to travel further.
Hope that helps.
Yes thank you. I was initially thinking they were talking about the roof surface in the valley changing slope. Which it doesn’t. But if I imagine walking up the roof on an angle, that’s the same principle as the valley in which the apparent slope is less.
The rise is the same, but the run is longer, forming a lower slope. The slope for the valley between two equal slope roofs is: (rise)/((run) x SQRT(2)). So, for two 6/12 (45 degree) sloped roofs meeting, the valley slope is 6/(12x1.414) = 6/(16.97) or 0.3535 radians = 4.242/12 = 19.47 degrees.
Marcel’s explanation is correct 
Think of the valley as being the hypotenuse of a right triangle which is always going to be longest side and will have a shallower rise.
