Roof Underlayment Calculator
Calculate roof underlayment costs by type and area. Compare felt, synthetic, and ice and water shield options.
How It Works
Enter roof area
Input total roof area in square feet with a 10–15% overlap allowance.
Select underlayment type
Felt 15lb, felt 30lb, synthetic, or ice & water shield for valleys and eaves.
Get material quantities
Receive square feet needed, roll count, and installed cost.
Frequently Asked Questions
What type of roof underlayment is best?
Synthetic underlayment is the current standard for most new roofs — it is stronger, more tear-resistant, lighter, and easier to walk on than felt. Ice and water shield (self-adhering membrane) should be used in valleys, eaves, and penetrations in climates with snow and ice. Felt paper (15 or 30 lb) is the traditional choice and still acceptable but inferior to synthetic for performance.
How much does roof underlayment cost?
Roof underlayment material costs $0.05–$0.50 per sq ft depending on type. 15 lb felt costs $0.05–$0.10/sq ft. Synthetic underlayment costs $0.10–$0.25/sq ft. Ice and water shield costs $0.50–$1.50/sq ft. Installed cost including labor runs $0.15–$0.75/sq ft for standard underlayment, plus ice and water shield in critical areas.
Do I need ice and water shield under the whole roof?
No — ice and water shield is typically applied at eaves (first 3–6 feet), valleys, and around all penetrations (chimneys, vents, skylights). In very cold climates, some codes require more coverage. For the rest of the roof, synthetic underlayment is used. Full ice and water shield installation is only required in specific high-risk areas or certain local building codes.
How long does roof underlayment last?
Synthetic underlayment lasts 25–50 years, similar to modern shingles. Felt paper lasts 15–20 years. Ice and water shield lasts 25–40 years. Underlayment should always be replaced when new shingles are installed — never install new shingles over old underlayment. Exposed underlayment (without shingles) degrades quickly in UV light, usually within 6 months.