How does roof underlayment cost compare by type?
The three main types
- Asphalt saturated felt in #15 and #30 weights. The traditional choice. It can wrinkle when wet and tears more easily under foot traffic and wind.
- Synthetic underlayment. Woven or spun polymer sheets. Lighter, stronger, and rolls typically cover several squares each, so fewer seams and faster installation. Now the standard on most replacements.
- Self-adhered membrane, often called ice and water shield. Rubberized asphalt that sticks to the deck and seals around nails. Used in valleys, around chimneys, skylights, pipes and at walls.
How it is priced on an estimate
Field underlayment is usually built into the per square or total price. Ice and water shield shows up separately, by the square or by the linear foot of valley. Insurance estimates list each as its own line.
What the code expects
The residential code requires underlayment beneath asphalt shingles, with a double layer on slopes between 2/12 and 4/12. Ice barrier at the eaves is required only where local officials say ice damming is a risk, which is uncommon in most of Georgia, so check with your building department, especially in the mountains.
Where spending a little more pays
Synthetic over the whole deck, and self-adhered membrane in every valley and around every penetration. Some homeowners go further and seal the entire deck, a step used in stronger wind programs. Compare in synthetic underlayment vs felt and ice and water shield in Georgia.