Last reviewed October 31, 2026.
Two quotes for the same Cape sit side by side on the table. One puts ice and water shield at the eaves and in the valleys. The other runs it over the entire roof deck. Same shingle, same crew size. This one material is where the two scopes split.
Homeowners call it ice and water shield. Manufacturers call it a leak barrier, a waterproofing underlayment or a self-adhered ice and water barrier. The state code calls it an ice barrier.
How the membrane differs from the sheet beside it
Regular underlayment gets fastened to the deck and sheds water. The membrane grabs the wood and holds on. Section R905.1.2 of New York’s 2025 residential code describes an ice barrier as either two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet used in place of the normal underlayment.
CertainTeed’s product page for WinterGuard HT X says the membrane has to go on a clean, dry, bare deck, never over shingles. The crew can reposition it before it bonds to the wood, and this version is built for the heat under a metal roof. CertainTeed warrants it to stay watertight for as long as the shingle warranty above it runs, up to 50 years.
The ordinary sheet across the rest of the deck, felt or synthetic, has its own roof underlayment page.
Reading section R905.1.2 line by line
The rule kicks in where Table R301.2 records a history of ice forming along the eaves and backing water up. Where it applies, it covers asphalt shingles, metal roof shingles, mineral-surfaced roll roofing, slate and slate-type shingles, and wood shingles and shakes.
- Distance. From the lowest roof edges to a point 24 inches or more inside the exterior wall line.
- Steep roofs. At 8 in 12 or steeper, at least 36 inches measured along the slope from the eave edge.
- Exception. Detached accessory buildings with no conditioned floor area, such as an unheated garage or shed.
Why ice dams form in the first place, and how to clear one, is on the ice dam guide.
Which Long Island towns check the yes box
New York does not fill in the ice barrier column for the whole state. Every municipality completes that table on its own. Smithtown’s listing page walks through the town’s table, written for the 2020 code, where the town wrote yes. The Islip town page explains why we have not seen Islip’s yet.
For every other address, ask the building department that issues the roofing permit. Contact details sit in the permit guide, town by town and village by village.
Valleys, shallow pitches and the spots around a chimney
The eave is only the start. CertainTeed’s underlayment page also puts the membrane along the roof’s perimeter, in the valleys, and around skylights, plumbing vents and the joints where a roof meets a wall. Its WinterGuard HT X page lists low-slope roofs as a common use.
The code backs up the valley part. Section R905.2.8.2 says valley linings go in following the manufacturer’s instructions, before the shingles. For a closed valley, the kind covered over with shingles, it accepts a self-adhering ASTM D1970 sheet at least 36 inches wide. For an open metal valley, it calls for a lining at least 24 inches wide.
For shallow pitches, section R905.2.2 requires a double layer of underlayment on shingle roofs pitched at least 2 in 12 but under 4 in 12. A single layer of self-adhering ASTM D1970 membrane is the other option Table R905.1.1(2) accepts there, and CertainTeed lists low-slope roofs among the uses for WinterGuard HT X.
Old membrane under a new roof
Section R908.3 normally means stripping a roof down to the deck. Then it carves out an exception. An existing ice barrier still adhered to the deck can stay when the sheathing is not water-soaked or deteriorated. It can even take an additional layer on top, where the roof covering maker and the new ice barrier maker allow it.
Owens Corning goes further than the code in its System Protection terms from August 2026. It requires a clean deck with all old roofing removed, and it names felt and ice and water membrane in that list. If the quote promises that warranty, the old membrane comes off.
Full deck coverage and the warranty
Some roofers offer the membrane over the whole roof. Owens Corning’s August 2026 warranty counts a qualifying self-adhered barrier over the entire deck as meeting two requirements at once: synthetic underlayment, and ice and water. Its qualifying barriers are WeatherLock, Titanium and RhinoRoof.
We found no Long Island price for full coverage. Ask for it as its own line, so those two quotes on the table line up fairly.
How the membrane laps over the metal at the eave is laid out in our drip edge guide.
