Roofing component

What is ice and water shield?

A sticky-backed rubberised membrane that seals itself around every nail driven through it — the underlayment for the places a roof is most likely to leak.

Updated September 12, 2026 · Every figure links to its source · Sources

DefinitionComponentAlso called: ice barrier, self-adhering underlayment, peel-and-stick

Ice and water shield — a self-adhering sheet of polymer-modified bitumen, applied directly to the roof deck under the covering, that bonds to the deck and seals around fasteners driven through it; "Ice & Water Shield" is a trade name that has become the trade's word for the class, and the 2021 IRC, Section R905.1.2 names the material as one way of providing the ice barrier it requires at the eaves.

What it is

The sheet is a rubberised asphalt compound on a polyester or polyethylene film, with a release liner on the back. Peel the liner, press the sheet to the deck, and it sticks; drive a nail through it and the compound closes around the shank. That self-sealing is the point — ordinary felt or synthetic underlayment sheds water that runs over it but does nothing about water that stands on it or follows a nail down. The Asphalt Roofing Manufacturers Association publishes technical bulletins on the product class, and the code standard for it is ASTM D1970.

Where it goes: along the eaves, as the IRC's ice barrier (to at least 24 inches inside the exterior wall line where ice dams have a history); down valleys; around chimneys, skylights and pipes; along the break of a gambrel or the low pitch of a shed dormer; and, in the IBHS FORTIFIED sealed-deck option, over the whole deck or over every sheathing seam.

Why it matters

The places listed above are where roofs leak. Water ponds behind an ice dam and stands in a valley; nails cluster around a chimney; and after a windstorm the deck may be all that is left. A membrane that seals to the deck turns each of those from a leak into a nuisance. The directory's entry on underlayment for metal roofs explains why the material also matters under metal, where high-temperature grades are needed.

The cautions are practical. It must go on a clean, dry deck and, on most products, over the drip edge at the eaves; it is not a walking surface in the heat; and a deck covered entirely with a vapour-impermeable membrane needs the attic ventilated properly, because moisture can no longer dry outward through the sheathing.

What it costs and who does it

Priced by the roll or the square as a line on the re-roof estimate, ice and water shield costs several times what felt does per square, which is why it is normally confined to the eaves, valleys and penetrations unless a full sealed deck is specified. The roofing crew installs it. Ask the estimate to state where it runs and how far up from the eave; "ice and water at eaves" without a dimension is not a specification. The directory's guide to a new roof installation shows where it sits in the sequence.

Frequently asked questions

Short answers; the sections above carry the detail and the sources.

Is ice and water shield required by code?

The 2021 IRC (Section R905.1.2) requires an ice barrier at the eaves in areas with a history of ice damming — either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet, extending at least 24 inches inside the exterior wall line. Local codes decide where the rule applies.

Should ice and water shield cover the whole roof?

It can, and the IBHS FORTIFIED sealed-deck option allows it, but a fully covered deck must be matched with proper attic ventilation because the membrane is a vapour barrier. Most roofs use it at eaves, valleys and penetrations and synthetic or felt underlayment elsewhere.

Does ice and water shield go over or under the drip edge?

At the eaves it goes over the drip edge, so water on the membrane runs out over the metal; at the rakes the drip edge goes over the underlayment. Follow the product’s instructions where they differ.

Find a roofer who does this

Where the membrane runs is a detail a good estimate states in inches. The directory lists roofing contractors by state and city.

Find a roofing contractor for a re-roof

Sources

2021 International Residential Code, Chapter 9: Roof Assemblies — International Code Council (ICC)
Technical bulletins on asphalt roofing — Asphalt Roofing Manufacturers Association (ARMA)
FORTIFIED Roof: requirements and rated roof covers — Insurance Institute for Business & Home Safety (IBHS)