No need for precise measurement.
No cut valley roofing.
When you have cut to a point opposite the top of the valley cut the rolled roofing straight up the main roof.
The shingles on the cut edge plane are.
Leave this top end beyond the ridge loose.
Then rather than cutting the shingles on the high volume roof plane a row of shingles is installed with the exposure edge facing the valley center.
Plus cutting the closed cut valley shingles can happen after the rest of the roof is shingled.
This layering will help direct the water into the valley and down the roof preventing leaks.
Closed cut valley even if i work toward the valley with three tab shingles cut valleys are faster than woven valleys hands down.
A chalk line is then used to strike a line from the top of the valley to the bottom of the valley.
For an open valley the installer should snap two chalk lines defining the cut edges of the valley on either side of the center line.
You have to cut the shingles back to 1 inch from the centerline.
Make a cut back down into the roll from the cut edge to within v2 inch of the top of the ridge.
It is essential to only use whole not cut shingles during this step.
It installs and looks almost the same as a regular cut valley where the shingles on the low volume roof plane are installed first and pass through the center of the valley by at least 12 in.
This cut down to the top of the ridge will let the 6 inch overlap lie flat in the far valley.
As you install roof shingles on the second roof plane you allow them to lap over the valley on top of the first shingles.
The shingles are then cut out of the valley area opening the surface of the valley lining to water run off and the environment.
Draw a 2 inch self stick flashing down the center.
With a closed cut valley there s no need to shingle the two roof planes at the same time.
In summary during the installation of a closed cut valley you install the first roof plane s shingles into the valley.
With an open valley a strip of metal will be visible on the roof wherever two opposing roof planes meet.
