Roof Ice and Water Shields & Underlayment: What You Need To Know

Have you ever wondered what goes into putting on a new shingled roof? Are there layers between the roof decking and the shingles? If so, what are they?

An important component of making your roof less prone to leaks caused by ice damming is an ice and water shield. This is a code requirement in cold weather states. If you have a more complicated roof with valleys, skylights, dormers, vent pipes or chimneys, it’s a good idea to have ice and water shield installed in and around these areas as well as along the eves.

What Do Ice and Water Shields Do?
An ice and water shield is a modified self adhered leak barrier. It comes in a sheet with split back release film – similar to a self-stick or peel-and-stick. It seals itself around the nails used in shingling. This rubberized material that helps to prevent leaks due to:

  • Water damming in your gutters
  • Wind driven rain
  • Ice dams
  • Vulnerable areas of your roof at the eaves and rake edges
  • Chronic problem areas of your roof like skylights, dormers, vent pipes, chimneys, and other areas covered by flashing.

Not All Roofing Underlayments Are the Same
The ice and water shield is an amazing roofing product that was first introduced in the 1980s. If you have a roof that you know to be older than 1980, it won’t have this great product under the shingles. After that time, it quickly came to be used by most companies to create better roofing systems, whatever the weather.

Traditional Felt Paper
If you see ice and water shield being installed, you might think it is felt paper. Felt paper or tar paper is also a rolled material you see roofers nailing down under shingles. It’s an asphalt saturated paper that increases the water resistance of your roof from wind driven rains or blow offs. Felt paper is also code, and many states have varying requirements as to its application.

Felt paper relies mainly on gravity to do its job helping to keep water out of your roof. It is effective when installed properly – in layers. Nail holes from shingles can pose a problem with felt paper, as any holes become vulnerable to seepage. It also can’t protect against any water that flows upward toward the top of your roof, like ice and water dams or heavy rain and wind storms.

Synthetic “Felt” Underlayment
Synthetic underlayment, like an ice and water shield, is quite a bit lighter, rolls out in large rolls, and is made of polypropylene, fiberglass, polyethylene, and polyester. It is a lot more efficient at preventing leaks and is thinner. Synthetics hold up better in the case of blow offs because they don’t tear like felt paper can. While they don’t seal the nails as ice and water shield does it is a superior underlayment when compared to traditional felt paper.

Synthetic “felt” is better at protecting your roof in the event of blow offs or wind driven rain, as it is not as prone to the same problems as felt paper. It will keep your roof dry even when water flows backward and in driving rain. It lasts longer and degrades more slowly than an asphalt product and is safer and easier to install. However, it is more expensive.

Take Away
Ice and water shield is a great product that can be used in spots to protect the most vulnerable areas of your roof, or as a whole-roof underlayment to protect from ice dams, water dams, storms, and leaking in any area of the country and any weather.

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