Four Ways to Shingle a Valley
Builder Mike Guertin shows three conventional ways and one newer method for weatherproofing this crucial roof detail.
Synopsis: This article illustrates four different methods of shingling a valley, comparing the advantages and disadvantages of woven, open metal, closed cut, and Long Island valleys and describing the author’s techniques for preparing and installing each one.
A lot of today’s new home designs include multiple gables and roof configurations. When two roof planes meet at an inside corner, a valley is created. 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.
For this article, I mocked up a section of roof to show four ways to shingle valleys. The mock-up allows me to show all four methods in a similar context. I used three-tab shingles for two of the methods and laminated shingles for the other two. When shingling a roof with three tab shingles, it’s easiest to shingle the roof planes first, working toward the valley. Laminated shingles let you start in the valley and work outward, which can be an advantage in some situations.
Preparing a roof: All valleys start the same
Regardless of the shingling method, every successful valley installation begins with proper roof preparation. Taking the right steps before applying the shingles not only goes a long way toward preventing roof leaks, but it also helps to cushion the shingles (or metal valley) against the ragged edges of the roof sheathing at the centerline of the valley.
In the past, I’ve used several different methods to prepare a valley, including lining the valley with aluminium coil flashing or roll roofing, and even cementing together layers of #30 felt paper with asphalt roof cement (a messy job). Today, fortunately, we have a simpler and more effective material at our disposal: waterproof shingle underlayment (WSU). Examples are Grace Ice & Water Shield, Weather watch, and Moisture Wrap. These peel-and-stick membranes seal around nails and are pretty easy to work with. A release sheet on the back keeps the membrane from adhering until you remove it.
I begin the prep work by sweeping off any sawdust or other debris. I also set any sheathing nails that stick up from the roof plane and could puncture or wear through the WSU or shingles. As with any asphalt-shingling job, I install a 9-in. to 12-in. strip of WSU along the eaves’ edges, and I crosslap the strips at the valley. These strips go under the drip edge.
I overlap the inside corner of the drip edge at the valley to minimize sharp edges that could cut into the WSU over time. Because I build in snow country and along the coast, I include extra protection along the eaves. After rolling out full 3-ft. widths of WSU over the drip edge and up the roof sheathing, I again overlap the WSU at the valley.
We used the term “Long Island Valley” to identify one type of valley. There are other names for the valley style: No-Cut Valley, Tamko Valley (Tamko brand shingle instructions show this as a preferred method), California Valley.
Check with the shingle manufacturer to see if they approve of the method if you are concerned about warranty coverage. Several companies approve of the method though they don’t include it in their instructions.
For more photos and details on the different ways to shingle a valley, click the View PDF button below.