Answers · What the work involves
What is ice and water shield, and do I need it?
The short answer
It is a self-adhering waterproof membrane laid directly on the deck, usually at the eaves, in valleys and around penetrations. It seals around nails, so water that gets past the shingles — from an ice dam or wind-driven rain — cannot reach the deck. Many cold-climate codes require it at the eaves.
Where it belongs
- At the eaves, running up the slope far enough to pass the exterior wall line. How far is set by code and by roof pitch, and it is worth asking what the quote specifies.
- In valleys, which carry the most water on the roof.
- Around chimneys, skylights and pipe penetrations.
- On low-slope sections, where water moves slowly and has time to find a way in.
Why it is not ordinary underlayment
Ordinary underlayment is a water-shedding layer with nail holes through it. The self-adhering membrane bonds to the deck and seals around each fastener, which is the whole point: it is the layer that works when water is sitting on it rather than running off it.
Also asked
- Do I need it in a warm climate?
- Ice dams are not the only reason for it. Valleys, penetrations and low-slope sections benefit anywhere, and wind-driven rain is a real load in hurricane and severe-storm regions. Local code will set a minimum; the valleys and penetrations are worth doing regardless.
General information about roofs and about hiring, not advice about your building. Roofing contractor licensing, permits, insurance practice and deductible rules are set state by state and province by province across the United States and Canada, so your own authority is the current answer.