The three methods to shingle a roof valley.
Using paper in a roof valley.
Use a broad strip of felt paper.
First clean the debris out of the valley including sawdust nails and whatever else is in there.
Start at the top.
Fold the top over the roof ridge and cut the bottom along the drip edge metal.
Roll out and smooth the wsu and drive a few nails on one side to hold it temporarily.
You can center it and align it smoothly with the roof contours as you go down.
Install synthetic roofing underlayment or felt paper according to manufacturer specifications and then install the first piece of valley flashing.
Fold over the other side and peel off the paper backing.
Woven valley shingle installation.
With a clean valley you can lay down some peel and stick roofing membrane.
To achieve a woven valley installation a roofing professional lays shingles in the valley and weaves them.
Lay the felt paper from the top of the roof valley to the eaves at the roof edge.
Snap chalklines on both sides for guides.
Felt paper should extend at least 10 inches up each side of the roof valley so use a strip between 20 and 24 inches wide.