Ice and water shield is a self-adhering waterproof membrane installed under the shingles at a roof’s most leak-prone spots — eaves, valleys, and penetrations. Unlike regular underlayment, it seals around nails, so water that gets past the shingles still cannot reach the deck. It typically adds $300 to $1,200 to a reroof, and in cold-prone or leak-history areas building codes require it at the eaves. Here is exactly where it goes, when it is required, and where it is worth paying for even when it is not.
Where ice and water shield goes on a roof
| Location | Why | Priority |
|---|---|---|
| Eaves (first 3 to 6 ft up from the edge) | Ice dams and gutter backups push water under shingles here | Required by code in ice-dam regions |
| Valleys | Highest water concentration on the roof | Strongly recommended everywhere |
| Around penetrations (vents, skylights, chimneys) | Flashing transitions are where leaks start | Strongly recommended |
| Low-slope sections (2:12 to 4:12) | Slow drainage gives water time to migrate | Code-required under some systems |
| Entire deck | Maximum protection | Optional — overkill on most steep roofs |
What it actually is (and how it differs from underlayment)
Ice and water shield is a rubberized asphalt membrane with a peel-and-stick backing. Two properties make it different from felt or synthetic underlayment: it bonds directly to the deck, and it self-seals around every nail driven through it. Regular underlayment sheds water; ice and water shield waterproofs. That is why it goes at the spots where water is most likely to sit, back up, or concentrate.
When code requires it
The residential code requires an ice barrier at the eaves in regions with a history of ice dams — extending from the edge to at least 24 inches inside the exterior wall line. In the Pacific Northwest, most lowland jurisdictions do not mandate it the way snow-country codes do, but many local inspectors expect it on low-slope sections and valleys, and manufacturers require it in specific assemblies for the warranty to hold. Your contractor should be able to point at the local requirement, not guess at it.
What it costs
| Item | Typical cost |
|---|---|
| Material (per 66-ft roll, ~2 squares) | $40 to $90 |
| Standard package on a reroof (eaves + valleys) | $300 to $700 |
| Extended package (eaves, valleys, all penetrations, low-slope areas) | $600 to $1,200 |
| Full-deck coverage | $1,500 to $3,000+ — rarely worth it on steep roofs |
On a $15,000 to $25,000 roof replacement, the standard package is 2 to 4 percent of the project — cheap insurance at the exact spots where roofs actually fail. In our climate, valleys and eaves under tree cover are where we see the payoff, since needle debris keeps those areas wet for months. See how it fits the whole assembly in our roof replacement cost guide.
FAQ
Is ice and water shield required in Washington State?
Not universally. Most lowland Washington jurisdictions do not require the full ice-barrier provision, but many inspectors expect it on low-slope sections and in valleys, and some manufacturer warranty assemblies require it. Mountain and colder-zone jurisdictions do enforce the eave requirement. Your permit jurisdiction decides — a local contractor will know.
Can ice and water shield go over the whole roof?
It can, but on a steep roof it is usually money better spent elsewhere. Full-deck membrane also reduces the deck’s ability to dry inward, so ventilation has to be right. The standard eaves-valleys-penetrations package covers the spots where nearly all leaks start.
Does ice and water shield replace underlayment?
No — they work together. The membrane goes at the vulnerable zones first, and regular underlayment (felt or synthetic) covers the remaining field of the roof, overlapping the membrane so water always sheds downhill onto the layer below.
How long does ice and water shield last?
As long as the roof above it — 20 to 30 years under asphalt shingles. It is not a maintenance item; once installed and covered, it does its job until the next reroof.
Can you install ice and water shield on an existing roof?
Not without removing the shingles above it — it bonds to the bare deck. That is why the time to get it right is during a reroof, and why we photograph the membrane installation before shingles cover it.
Get the membrane details right the first time
The Roofing Titan installs and repairs roofs across Kenmore, Kent, and Greater Seattle with the edge, flashing, and underlayment details built for Pacific Northwest weather. Request a free inspection with a photo report and get a straight answer on what your roof actually needs.