Because valleys collect and channel a greater volume of water than a single roof plane i always make an extra effort to design and build them as watertight as possible.
How to tie in valleys on shingle roofs together.
With a clean valley you can lay down some peel and stick roofing membrane.
First clean the debris out of the valley including sawdust nails and whatever else is in there.
Measure between that truss or rafter and the valley rafters with a tape measure and cut short rafters to tie the old and new rafters together.
The roofing cement will resist possible leaks overnight.
After the addition roof is framed and sheathed snap a line on the existing roof shingles 2 in.
How to shingle a valley with architectural shingles.
Fold the top over the roof ridge and cut the bottom along the drip edge metal.
When two roof planes meet at an inside corner a valley is created.
At the low end of the valley the subfascias of the two roofs are mitered with a block filling in the roof framing.
Ensure ice and water protector has been installed along the valley first.
Drip edge metal valley flashing dormer chimney and kickout flashing are types of roof flashing that shed water away from the connections between roofs walls chimneys and other building assemblies.
Only nail at the edges with only enough nails to hold it in place.
Up from the valley center and cut through the shingles and underlayment.
To transition the eaves the horizontal fascia extends to the last rafter tail and a vertical return finishes the transition.
The easiest way to tie in the new shingles with the old is with a cut valley see four ways to shingle a valley.
Sheathing blocking is added along the valley and the sheathing pieced in for both roof planes.
To shingle out of the valley with laminated shingles lay a shingle down as a gauge and mark the corner at the bottom left and top right of the roof.
Use a speed square to find the proper angles and cut.