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Here’s a question that builders ask a lot: What is ice and water shielding? And more importantly, when is it necessary? Where Epilay’s synthetic underlayment roofing products are concerned, our Plystik Plus, which is a peel-and-stick underlayment, features Ice Dam Protection. This means that Plystik gives extra protection against harsh winter elements like ice. Additionally, because it’s a peel-and-stick underlayment, it serves as an excellent non-permeable water barrier that shields roof decks from moisture. This underlayment is one that is considered an ice and water shield.

But back to these two questions! Let’s answer them so that you can see how products like Plystik help protect roofs, and so that you know when to use this type of underlayment.

What is Ice and Water Shielding?

In a nutshell, underlayments that offer ice and water shielding are a waterproof membrane designed to protect a roof deck against damage from ice, melting snow and rainwater. These underlayments are always of the peel-and-stick variety. The reason for that is because non-adhesive underlayments installed with fasteners can’t be considered truly waterproof since there is always the chance for some moisture to seep in around fastener punctures.

With a peel-and-stick underlayment, the adhesive is designed to seal around nail punctures to keep water out. The adhesive also means that laps along the sides and edges of the underlayment seal, too, which is another way this underlayment protects against moisture damage.

When to Use Ice and Water Shield

The first thing to do is check with local building codes. In some areas, ice and water shielding may be required. But even if it isn’t required, in most areas, this type of underlayment is often still a wise choice because it serves as an added layer of protection against moisture.

In particular, these underlayments are a good choice in areas that experience severe weather. For instance, in hurricane-prone areas or areas that regularly see high winds, peel-and-stick underlayments help protect the roof deck from rainwater even if shingles are torn off in the wind. When shingles remain intact, the underlayment still protects against threats like wind-driven rain, which can be blown underneath shingles.

They’re also a good idea in northern climates where snow and ice gathers on rooftops. Again, if shingles should be torn off when snow or ice breaks free, the underlayment serves as protection until repairs can be made. Another reason why peel-and-stick is a great choice in snowy areas is because as snow and ice melts and refreezes, this creates an ice dam on the roof. Ice dams form when meltwater refreezes along the roof’s soffit, thus trapping additional moisture as it flows down from upper parts of the roof. Water trapped by ice dams can make its way beneath shingles, and the underlayment is necessary to protect against this seepage.

In fact, ice and water shielding is even more important on low-sloped roofs or in roof valleys, particularly in snowy areas. That’s because on low slopes and in valleys, there is an increased risk of water pooling, which means the underlayment is a necessary defense against moisture damage. Builders will often use ice and water shield around the edges of the roof to protect against ice damming, plus in valleys and around chimneys and other fixtures prone to leakage. To reduce costs, they’ll then use a standard non-adhesive underlayment elsewhere on the roof.

As you can see, ice and water shield isn’t always necessary, though in some places, it is required by code. And in areas prone to high winds and snow, ice and water shield becomes very important for the safety of the roof deck below.