Ice and Water Shield (Self-Adhered Ice Barrier)

"Ice and water shield" is the common trade name for self-adhered underlayment membranes, usually rubberised or polymer-modified bitumen with a peel-off release film and a surfacing of film, sand or fabric. The membrane bonds directly to the roof deck and seals around nail shanks driven through it, so it resists water that is pushed uphill under shingles or tiles. Building codes call it an ice barrier, and in Canada the comparable requirement is called eave protection.

Why it is used

In cold climates, heat escaping from a house can melt snow on the upper roof. The meltwater refreezes at the colder overhang, forming an ice dam, and water ponds behind it and backs up under the roof covering. A sealed membrane at the eaves keeps that water out of the building.

Code requirements (United States)

Under International Residential Code section R905.1.2, where the local jurisdiction has a history of ice forming at the eaves, an ice barrier is required. It must extend from the lowest edges of the roof surfaces to a point at least 24 in (610 mm) inside the exterior wall line of the building, measured horizontally. The barrier can be either at least two layers of underlayment cemented together or a self-adhering polymer-modified bitumen sheet. Detached accessory structures without conditioned space are commonly exempt; local amendments often extend coverage further.

Other common uses

• Valleys, where water concentrates.
• Around chimneys, skylights, and sidewall and headwall flashings.
• Low-slope sections and roof-to-wall transitions.
• Full-deck coverage in hurricane zones or under metal roofs, depending on manufacturer and code.

Cautions

Self-adhered membranes are generally vapour-impermeable, so covering an entire roof can affect how the assembly dries. Some products are not rated for the high temperatures under metal roofing, and the membrane should not be left exposed longer than the manufacturer allows.