How To Shingle A Roof Valley

We’ve been working our way through a series on how to use asphalt roofing shingles on your new home — or to renovate an existing one. We’ve covered all of the basics, and now it’s time to get to the specifics.

To start with, we’ll address one of the more common questions we get: how to shingle roof valleys.

Roofing a valley is always an interesting task to face. When it comes to asphalt shingles, it’s even more interesting; roofing a valley with Asphalt shingles is not the same as with other materials.

On the one hand this means learning new techniques. On the other, it’s actually one of the strengths of using roof shingles for your home. One of the nicest things about the valleys on a home with roof shingles is that they look seamless. The shingles flowing right through the valleys and blend perfectly with the rest of the house.

So whereas other materials give you a definite line break in the material at the valleys, with shingles, your roof achieves a much cleaner and more elegant look.

But, of course, looks aren’t the only consideration. That sleek, seamless appearance won’t mean anything if they aren’t waterproof. Roof valleys are a critical step in waterproofing a quality roof, and care needs to be taken.

There are many techniques to lay beautiful looking, waterproof roof shingle valleys. Rather than go through all of them, we’re going to show you one of the quickest, simplest — and effective — ways to do it.

Shingling The Roof Valley

It’s important to begin shingling your roof on the side that will shed the least amount of water. If you’re not sure what that is, it’s the side with the smallest roofing area.

To keep the valley watertight, we need to avoid any joins or nails in the valley. This is critical to maintaining the integrity of the valley, as well as to maintain that sleek aesthetic look that you’re after.

You do this in two ways.

  1. Ensure that a full shingle extends past the valley by at least 300mm.
  2. Do not nail within 150 mm either side of the valley centre line. Your goal is to have a 300mm nail-free zone across the valley.roof shingles in valley pressing down

As you nail in each valley shingle, you need to take care to push both the top and bottom of the shingle down. This will help you to prevent any bridging.

Continue laying down your asphalt shingles on that side of the roof until you reach the top of the valley.

We touched on earlier that there are many ways to shingle a valley. Which method is used largely comes down to the roofer’s preference and experience. If there’s a way they’re comfortable doing it, that they know delivers quality results, then that’s the right way.

To create a waterproof valley, some roofers will completely overlap the shingles from both sides. Then they’d hand cut off the excess material to create the smooth join.

This method takes a bit longer, but still creates a nice, clean line at the end.

If you don’t want to spend that much time on hand-cutting excess shingles, there are other ways to create the join when you start shingling the other side.

Cutting In The Shingles In A Valley

Now that you’ve got one side of the valley shingled, we obviously need to get the other side connected. Assuming you’re not using the double-overlap method mentioned above, you have a few alternatives.

“Closed Cut” method. The “closed cut” method is where the shingles from the other side run toward, then overlap, the centre line of the valley. So you start your line of shingles away from the valley, and work your way in.

A chalk line is laid down, and snips are used to trim the excess along the chalk line.

“Californian Cut” method. This method avoids physically cutting the shingles. Instead, a row of shingles running vertically up the valley is used to serve as our valley line. You start laying the shingles at the valley line, and work your way out, as opposed to the “closed cut” method.

To start with, you’ll need to snap a chalk line up the roof valley.

Thanks to gravity, more water will gather at the bottom of a valley than at the top. When creating your chalk line, create a valley line that “Opens Up” as it goes down. So at the top of the valley you might start around 35-40mm away from the valley centre line, and then open up to 65mm by the bottom.

Once you have your chalk line, run a bead of asphalt adhesive. Using that chalk line as your guide, start running a vertical line of shingles up your valley. Our clean valley line will be made by the edge of this line of shingles.

Since no cutting is actually required, this method is also just referred to as a “California valley”, rather than a “California cut”.

No matter which method you end up using, if you plan it right you’ll end up with a very clean, straight and waterproof valley.

GAF Asphalt Roof Shingles

So we’ve gone over how to install the shingles. But what shingles should you use? In Australia, we recommend and use GAF Asphalt Roof Shingles. They’re the genuine article from America; the leading brand used, installed on more roofs than Australia has houses. For quality and aesthetics, you cannot go past GAF asphalt roof shingles.

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