Valley Flashings Flashcards
Why are valleys considered weak spots in roofing systems?
Valleys have a lesser slope than adjacent roof planes, causing water to be directed into them, which leads to faster erosion.
What should inspectors check when examining roof valleys?
Inspectors should look at visible flashing and the adjacent roof covering at least a couple of feet on either side.
What are the two main types of roof valleys?
Open valleys and closed valleys.
How is an open valley defined?
Open valleys have roof plane coverings that do not overlap each other across the valley center, leaving the flashing material visible, as seen in most tile and wood shingle roofs.
How is a closed valley defined?
Closed valleys have flashing that is not visible because the roof plane material carries over from one plane to the next, common in asphalt shingle applications.
What materials are commonly used for valley flashing?
Valley flashing materials include roofing felt or tar paper, roll roofing, membrane material (ice and water shield), and metal flashing (galvanized steel, stainless steel, lead, or copper).
What are the requirements for open valleys on asphalt shingle roofs?
Two layers of roll roofing: an 18-inch-wide first layer face down, and a 36-inch-wide second layer face up, both cemented down with shingles cut back 3 inches from the centerline.
Metal flashing: at least 24 inches wide with a 1-inch-high center rib, nailed at 18 inches on center, not more than 1 inch from the edges, ideally with an ice and water shield layer beneath.
What is good practice when installing shingles in open valleys?
Cutting an angle on the top of the shingle helps stop water from migrating across the top of the shingle.
What are the two types of closed valleys?
Fully closed valleys and closed-cut valleys.
Describe a fully closed valley.
Shingles from both planes interweave across the valley and extend at least 12 inches onto the adjacent plane.
Describe a closed-cut valley.
Shingles from one roof plane cross over to the next, and the covering from the other plane is cut back 2 inches from the valley centerline.
What additional protection should be applied to valleys in closed and closed-cut designs?
Use one of the following over the normal felt or tar paper underlayment:
36-inch roofing felt or tar paper,
36-inch roll roofing, or
36-inch ice and water shield.
Where should shingles not be nailed in valleys?
Shingles should not be nailed within 6 inches of the valley centerline, and un-nailed areas should be cemented down.
