How To Install Step Flashing For Roof Shingles

Waterproofing is one of the most important aspects to consider when installing a new roof. Whether it’s a renovation, new build, or knock-down rebuild, keeping the roof waterproof demands your utmost attention.

There are lots of places where special care is needed to ensure the roof doesn’t leak. Roof valleys are a major one, and we’ve written extensively in the past about how to maintain their integrity.

Another key area is where the roof butts up against a wall. This might be because of a dormer window, or a second level that only rises above part of the house. In these areas, any builder knows you’ll need flashing to keep the area water tight.

Most Australian builders, though, are used to working with tin or tile. For these, you can use long lengths of flashing to achieve a solid seal.step flashing roof

With asphalt roofing shingles, however, you need to adjust your method a bit. Instead of one long piece of flashing, “step flashing” is used instead.

Step flashing isn’t a new concept, and it’s not actually exclusive to roof shingles. It is, however, something that a lot of people get wrong. This leaves home owners and renters with the unfortunate circumstance of dealing with water damage the second there’s a half-decent downpour.

Since the cost of properly installing step flashing is much, much lower than fixing extensive water damage, (and much easier than retrofitting it) it’s better to get it right the first time.

Without further ado, here’s how to install flashing for asphalt roof shingles

Why Step Flashing is Important for Roof Shingles

Any join on a roof is a leak risk, and where a roof meets a wall is one of the most critical, leak-prone areas. That’s why a flashing system is required to keep the area water tight.

For asphalt roof shingles, the only type of flashing you should be using in these areas is step flashing. Regular, continuous-length flashing can be used on the front wall of a shingled roof, but never the side walls.

step flashing leaks

Yes, it takes more time and care to install. But without it, you’re going to get water leaks. Water will always find its way between the shingles and flashing. Capillary action will then cause the water to seep down at an angle of about 30-40 degrees, running off the side of the flashing.

This is how and where your leak occurs.

You can try to install your long length of flashing on top of or below the shingles — it won’t matter. You’ll still end up with a leak.


Now, keep in mind — water will still find its way between the shingle and step flashing. Why is that not a problem? Because with step flashing, the only place the water can go is over the shingle beneath it. That will draw the water away and down to the gutter.

So the first big mistake to avoid: do not use long lengths of flashing on asphalt roof shingles.

How To Install Step Flashing

You’ll want to start at the corner of the front and side wall. We recommend using step flashing approximately 150 by 120 by 250mm long. This is longer and wider than you’ll usually find, but we’d rather have that extra overlap beyond the reveal line. It provides additional protection, and minimises the chance of water seeping under the flashing.

Attach the first step flashing, making sure it extends about 30 to 40mm past the corner. This will ensure water runs off away from the vulnerable corner and down the roof to the gutter.

After the first step flashing is nailed down, install a shingle over it. You want to continue adding a step flashing as you shingle each row up the roof. Once you’ve gone completely up the side and apply the wall cladding, you’ll have a discrete waterproof system that will protect your home for years to come.

Completing Your Asphalt Roof Shingle Roof

step flashing front wall

We love asphalt roof shingles, and we’re dedicated to bringing this great roofing product to Australia. That’s why we’re putting out guides for installing your new roof properly using roof shingles. It’s not crazy difficult, but it does require some different steps to normal.

With American-style homes gaining popularity in Australia, we feel it’s important to get the authentic product to really bring the style together. There’s no sense in going to the effort in building these timeless American style structures, only to top it off with a completely inauthentic roof.

Tin is right out. Tile roofs just don’t have the same look and feel of roof shingles. They’re a good approximation — but not quite there.

You need the right product. We proudly stock GAF asphalt roof shingles — the leading supplier of asphalt shingles in America. They not only produce shingles, but most of the other materials necessary to build a sturdy, waterproof roof for your home. From shingles to gutter covers, GAF can provide all the material you need to put your roof together.

Read the rest of our articles to find out more about how to install asphalt roof shingles, or feel free to give us a call. If there’s something you want covered in these articles, let us know.

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