Which GAF Roof Shingle underlay to choose, and how to install it.

Asphalt roof shingles are a great material for the Australian climate. They look good, they’re inexpensive, they provide insulation – what’s not to love?

While the look dominates in American homes, it’s only really starting to grow in popularity here.

That’s why we’re putting together articles on the different aspects of building a roof using roof shingles.

When installing roof shingles, there is a very important underlay that sits between the plywood roof deck, and the shingles themselves. This underlay, also known as sarking, is a breathable material that plays an incredibly important role in the overall roof shingle installation.

GAF DeckArmor underlay

The sarking is applied over the entire plywood roof deck, and provides the final leak barrier before the roof shingles are finally laid down. It truly cannot be overestimated how important this layer is.

In this article we’ll discuss which underlay to use, and how to correctly install it.

Preparing the Plywood

Before applying the underlay, you need to pay special attention to ensuring the plywood itself is properly prepared.

Have a hammer handy and walk the entire section of plywood that you are about to cover. You want a smooth surface to start applying the sarking to, so you need to check for nails that haven’t been driven down all the way.

Use your hands if you have to, in order to feel any high nails. Hammer any offending nails down into place.

You also want a clean surface to apply the sarking to. Once you’ve found all of the remaining high nails, brush the surface or use a blower. You want to clear away dust and dirt off the plywood to have the ideal contact surface.

Applying the Underlay

Start at the eaves.

Overlap the drip edge and begin rolling out the underlay until you reach a hip or valley on the roof. Cut off the excess while still allowing for a bit of overlap.

GAF Deck Armor InstallationWith the first row aligned with the eave line, begin nailing down the underlay. This locks it into place and allows the roofers to start to safely walk over it.

One of the key features of the underlay is to reduce any moisture build up.

That’s why you don’t want to use a complete air and vapour barrier. These can become breeding grounds for moisture and mould which can lead to serious problems.

GAF, who produce the USA’s most popular asphalt roof shingles, offer a wide range of underlayment options.

Deck Armor is their current underlay flagship product.

Deck Armor has a breathability rating of 16 perms, far superior to any other deck underlay on the market.

Once the first row is nailed in place, you can begin the process again of rolling out the second row. You will need to have a bit of an overlap between one layer of sarking and the next, to ensure a proper seal.

Once in place, nail it all down. Repeat the process as necessary to cover the entire section of roof.

Once the underlay has been spread over the whole roof, you can start to attach the shingles and finish your new roof!

The Importance of the Underlay

We’ve mentioned already that the underlay is an important feature of the roof shingle system.Nailing In GAF Deck Armor

Above, we described that it’s a breathable moisture barrier, but it also has other functions. For example, it helps to prevent the asphalt leaching out of the shingles and into the plywood.

Unfortunately it’s common for some shingle roofers skip using an underlay, typically as a cost-cutting measure.

This inevitably leads to a range of problems down the line, and greatly affects the longevity of the roof itself.

When to Use Roof Shingles

In Australia, we typically use tin or tile as our roofing material of choice. From the red centre to the sunny coastal beaches, you will always find tile and tin roofs across the country.

But sometimes we stick to these old favourites even when there are other, better-suited options around.

For example, we’ve noticed an increase in Hampton-style houses across the country in new developments. Hamptons-style homes are quintessentially American in design, but feel right at home in Australia.

With their tall ceilings, open-plan interiors and relaxed feel, it’s not surprising to see so many of them popping up along Australia’s coastlines.

But even these American style homes are being finished off with tiles.

An authentic Hamptons style home, like most homes in America, use roof shingles, not tile. It gives that distinct look to the roof that other materials just don’t have, and creates an authentic finish that other similarly designed houses are lacking.

Roof Shingles Underlay


Asphalt roof shingles are the single most popular roofing material in the USA, and GAF is the leading supplier.

There are more homes in America with GAF roofing shingles than there are homes in Australia!

We’re proud to offer GAF asphalt roof shingles, along with their other range of roofing materials. Whether it’s vital sarking underlay material, or waterproofing for roof valleys, GAF provides all of the materials and tools needed to make your next roof last.

If you’re interested in learning more about using roof shingles for your home or next property development, check through our articles for more detailed how-to guides.

Otherwise feel free to contact us today and we’d be only too happy to have a chat about our authentic GAF products to give your home that distinct American style.

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