What is peel and stick roof underlayment, and when should you use it?
Short answer. Peel and stick underlayment is a self-adhered membrane, usually rubberized asphalt with a sticky back, that bonds directly to the roof deck and seals around nails driven through it. It is standard in valleys, around chimneys, skylights and pipes, on low slopes and at eaves where ice dams can form, and some homeowners choose it over the whole deck for maximum water protection.
How it works
The membrane's rubberized asphalt grips the deck and closes tightly around each nail shank, so a fastener does not become a leak path. Products meeting ASTM D1970 are tested for that nail sealability and must be at least 40 mils thick. A plastic release film protects the adhesive until installation.
Where it belongs
- Valleys, where water from two slopes concentrates.
- Around chimneys, skylights, sidewalls and pipe penetrations, under the flashing.
- Low-slope sections where water moves slowly.
- Eaves in areas with a history of ice dams, mainly the North Georgia mountains.
Full coverage: pros and cons
- Pro: a sealed deck, so if wind strips the shingles, water still stays out.
- Pro: no fastener holes through the main water barrier.
- Con: higher material cost.
- Con: it blocks vapor, so the attic must vent well to avoid condensation under the deck.
- Con: it bonds so well that the next tear-off often damages the decking, adding cost to a future replacement.
Installation tips
- Clean, dry deck, with no dust or dew.
- Cut to manageable lengths and position before peeling.
- Peel split-back film one half at a time, pressing from the center out.
- Lap seams per the printed lines, shingle fashion.
- Use high-temperature versions under metal roofing.
See ice and water shield in Georgia and synthetic underlayment vs felt.