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Roof Underlayment Calculator
Roof underlayment costs $0.75–$4 per sq ft installed in 2026, or about $1,100–$9,000 for a whole roof. Asphalt felt runs $0.75–$1.50; synthetic $1–$2.50; ice-and-water shield $4–$5.50. Most modern roofs use synthetic across the field with ice-and-water shield in valleys and at the eaves. Use the calculator below to size and price your roof.
Educational calculators — always consult a licensed professional before making financial decisions.
Home footprint under 1,500 sq ft. Actual underlayment area is larger due to pitch factor and overlaps.
Traditional asphalt-saturated felt. Cheapest option (~$0.05/sq ft). Tears easily when wet; limited slip resistance.
Low pitch requires self-adhering or fully-adhered underlayment. Standard felt is not code-compliant below 4/12.
Standard installation for most residential roofs. Meets code in the majority of US climate zones.
Total underlayment cost
$337 – $805
1,320 sq ft — materials and labor
Cost breakdown
Where Your Money Goes
Underlayment is typically installed as part of a full roofing job. Standalone underlayment installation is rare except for staging or storm prep.
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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.
2026 Underlayment Cost by Type
| Type | Installed / sq ft |
|---|---|
| Asphalt felt (15/30 lb) | $0.75–$1.50 |
| Synthetic | $1–$2.50 |
| Ice & water shield | $4–$5.50 |
Per sq ft installed (material + labor) by type. National average estimate for 2026 ($1,100–$9,000 for a typical roof).
Felt vs. synthetic vs. ice-and-water shield
- Asphalt felt (15/30 lb): cheapest and time-tested, but heavier, tears easily, and wrinkles when wet. Fine for budget asphalt-shingle jobs.
- Synthetic: lighter, far stronger, water-resistant, and safer to walk on — now the default on most professional jobs. Costs a bit more but installs faster.
- Ice-and-water shield: a self-adhering waterproof membrane. Not used across the whole roof — it's applied in valleys, around penetrations, and along eaves in cold climates to stop ice-dam leaks. Building codes often require it.
How much do you need?
Underlayment is sold by the roll and measured in roofing squares (1 square = 100 sq ft). Multiply your roof's footprint by its pitch multiplier to get true surface area, then add 10–15% for overlaps and waste. Ice-and-water shield only covers the eaves (typically the first 3–6 ft up from the edge) and valleys, so you need far less of it than field underlayment. The calculator above does this math for you.
What's included — and what's extra
Usually included
- Field underlayment (felt or synthetic)
- Ice-and-water shield at eaves & valleys
- Fasteners / cap nails
- Labor to lay and overlap
Often extra
- Tear-off of old underlayment ($0.65–$3.20/sq ft)
- Decking repair / replacement
- Drip edge & flashing
- Steep-slope or multi-story access
When underlayment gets repaired or replaced
Underlayment is normally replaced as part of a full re-roof — you can't reuse it once the old shingles come off. You'd repair or replace a section on its own only after a leak, storm damage, or when the deck below has rotted. If your roof is being torn off anyway, upgrading felt to synthetic (and adding ice-and-water shield at the eaves) is a small, worthwhile cost bump.
Brands, contractor questions & warranty
Common brands: GAF (Tiger Paw, FeltBuster), Owens Corning (ProArmor), CertainTeed (RoofRunner), and Grace Ice & Water Shield for the self-adhering membrane.
Ask & watch for:
- Which underlayment, and is ice-and-water shield included at eaves and valleys?
- Does my area's building code require ice-and-water shield?
- Will you inspect and repair the decking before covering it? (Skipping this hides rot — a red flag.)
Warranty: premium synthetic underlayment carries a 25-year to lifetime material warranty and is often required to unlock a manufacturer's full roof-system warranty — keep the product records.
Methodology & sources
The cost figures on this page are generated from a single, sourced cost-data file (Per sq ft installed (material + labor) by type. National average estimate for 2026 ($1,100–$9,000 for a typical roof).). Felt is cheapest; synthetic is lighter, tougher, and now standard on most jobs; ice-and-water shield is required in valleys, eaves, and cold-climate roofs and costs the most. Labor is $0.65–$3.20 per sq ft. Last verified July 2026.
- HomeGuide — Roof Underlayment Replacement Cost (2026) — retrieved 2026-07-13
- Angi — Roof Underlayment Replacement Cost (2026) — retrieved 2026-07-13
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 costs $0.75–$4 per sq ft installed in 2026, material and labor together. By type: asphalt felt (15/30 lb) runs $0.75–$1.50 per sq ft installed, synthetic $1–$2.50, and ice-and-water shield $4–$5.50. Most roofs use synthetic across the field with ice-and-water shield only in valleys and at the eaves, so a typical job lands toward the lower half of that range.
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.
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Back to the calculator ↑Roof Underlayment Calculator is built and maintained by the RealCostIQ editorial team. Cost ranges and rates are checked against published industry data and contractor quotes, and revised when the underlying figures move. Read our data methodology or more about who builds this. Every calculation runs in your browser — no account, and none of your inputs are stored.
Cost ranges and rates here are checked against contractor quotes and published industry data. If a number still looks off, email Support@RealCostIQ.com and we'll review and fix it.