What is Valley Flashing?
In this video, I’m gonna show you how to install valley flashing on your shingle roof. Valley flashings, or the open valley, is a great way to waterproof your valley. You can see here, the valley flashings that we use is called the W-Valley, is the correct term. It’s 24 inches wide, which is California code. Some people do use 18, but 18 is not recommended, it does not meet manufacturer specifications, it does not meet California Building Code. So what this valley allows us to do is install the shingles, leaving a proper gap that allows the water to come, hit this ridge right here, and flow down the roof, just the way we want it to.
Valley flashings come in four different finishes. They come in the charcoal finish right here, which is a dark grey. They come in a brown, a white, as well as a galvanized finish. There’s other custom valleys available like copper and other materials like that. But generally, one of these three pre-finished valleys is what we recommend. These will last over 50 years, so they’ll outlast your roof and keep your roof waterproof for years to come.
Order of installation
Alright, we’re ready to start installing our valley metal. Now, before installing our valley, we wanna have our underlayment installed. You can watch in our previous videos that we have our ice and water shield installed already underneath our underlayment. So we’ve got our ice and water shield directly on the deck, we’ve got a drip edge installed, we’ve got our underlayment on top of that.
We’re gonna install our starter shingle, then install the first row of shingle essentially right here. Now, I’m not gonna nail this for right now, we’ll go ahead and nail this later. Then, we wanna place our valley and we wanna come out about two or three inches.
Marking and Placing the Valley Flashing
Now, depending on where you are and how you want the water to flow. In this case, I want the water to flow out, just to have it going in underneath my undershot, so I would prefer to have it out about three inches. Now, we can mark the top of the valley, get it cut prior to installing.
Do not place nails inside the flashing
Now that we have our valley cut, we’re ready to start installing it. So we wanna align it to where we need it in the bottom. In order to install it, we’re gonna be using a nail gun, with the electrogalvanized nails, the same nails that you would use to install your shingles. You wanna place nails every 12 inches on center. Now, the important thing is to make sure to nail at the outer edge of the flashing, as opposed to anywhere inside. You wanna leave the flashing as a nail-free zone. So you wanna minimize the amount of nails that you have here, so that any water that gets up here has no chance of coming
and dripping through a nail hole.
Installing shingles over the valley flashing
Now, that we have our valley installed, we’re gonna be installing our first piece of shingle. Now, we do this a little bit differently, and this is a technique that we like to use. We believe it just gives us a lot cleaner of a look and our finished product is nice and neat. What we do is install a shingle vertically with the valley. Now, the first thing you wanna make sure is to install or leave enough of a gap between the W-Valley and the edge of the shingle. Anywhere from an inch and a half to three inches is totally fine. If you have a smaller valley, an inch and a half is sufficient. If you have a long run, 20-30 foot run, you wanna use a wider gap in order to allow for proper drainage. Just like other concepts in roofing and in shingle roof installation, this channel right here is gonna allow the water to freely flow and will minimize debris buildup so you won’t have leaves or things clogging up the valley. It’s a nice clean middle channel for the water flow down freely. So we wanna measure it and make sure that this opening is straight. For this demonstration, we’re gonna be using three inch reveal. Now, a chalk line is definitely useful on a long valley to ensure that you have a straight run. A small valley like this, it is not a 100% needed, but on a longer run, it definitely helps to have a nice, clean and straight line.
Now, installing the shingle, we wanna nail directly on the SureNail strip, and I’ll show you the reason for that. Now, when we nail on the SureNail strip, that aligns perfectly with the edge of the flashing. So that ensures that we’re not too far in the SureNail strip. I’m gonna show you another example right here. This line with the edge of the flashing. So that’s the way we wanna see it. The next step is to actually start installing our rows of shingles. One advantage to doing it this way is we have the adhesive tab on the back of the shingle. This adhesive tab, when put on the metal flashing, creates a great bond. So on a hot day like this, within an hour or so, all those seal tabs are gonna melt and adhere up to the valley, making it very difficult to lift up.
Now that we have this vertical shingle installed, we’re ready to start installing our regular runs. So we’re just gonna align the first shingle up, make sure this corner is touching, then start installing. Now, for this example, we’ve cut the shingles in half, just as a demo roof, but generally, you would have your full shingles going across your roof and continuing. Now, one thing that you wanna keep in mind is usually our shingle offset, we wanna do it, if you watch our shingle video, five to five and a half inches between each shingle, as far as the stagger goes. So just depending on your pitch and how steep your valley is, you’re gonna have a different reveal here. So you might have to cut the shingles to continue your standard pattern across the roof. Now, one thing you wanna keep in mind is you wanna minimize the nails in the valley. So, actually, the first previous shingle I had nailed incorrectly. You wanna nail it at the edge of the valley flashing. So you’re gonna be right around here.
So there you have it. You can see here, we’ve got a nice clean line, it makes our job as installers faster because we’re not cutting the shingles. And however clean you try to cut it or however straight, you will never get a perfectly clean and straight line as you would in this installation method.