Roof Underlayment Types and Costs: Felt vs. Synthetic vs. Self-Adhering
Updated June 2026 · 6 min read
Underlayment is the layer your roofer installs directly on the wood deck before shingles go on — and it is the difference between a minor shingle problem and a soaked attic when weather hits. Most homeowners never think about it, but it is a line item in every roofing quote. Here is what each type does, what it costs, and when the upgrade to premium underlayment is worth it.
Roof Underlayment Cost Comparison — 2026
| Type | Cost / sq ft | 20-sq roof | Best for |
|---|---|---|---|
| 15-lb asphalt felt | $0.35–$0.55 | $700–$1,100 | Budget installs, mild climates |
| 30-lb asphalt felt | $0.45–$0.65 | $900–$1,300 | Better than 15-lb; still inferior to synthetic |
| Synthetic underlayment | $0.45–$0.85 | $900–$1,700 | Most new residential roofs |
| Ice-and-water shield (self-adhering) | $0.65–$1.05 | $1,300–$2,100 (full coverage) | Cold climates, eaves, valleys, penetrations |
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The three main underlayment types
Asphalt felt (15-lb and 30-lb)
$0.35–$0.65 / sq ft installedTraditional felt paper is saturated with asphalt to create a basic moisture barrier. 15-lb felt (also called #15 or Type I) is the thinnest and cheapest option. 30-lb (Type II) is heavier and more tear-resistant. Both are still widely used and meet minimum code requirements in most jurisdictions.
Advantages
+Lowest cost
+Widely available
+Accepted by most manufacturers as minimum warranty requirement
Limitations
−Tears easily when wet or walked on during installation
−Can wrinkle and buckle in heat
−Shorter exposed-installation window (24–48 hours before shingles needed) vs. synthetic
Synthetic underlayment
$0.45–$0.85 / sq ft installedSynthetic underlayment is made from woven or spun polypropylene or polyethylene. It has largely replaced felt on new residential roofs due to its superior performance characteristics. Most major roofing contractors now use synthetic as their standard.
Advantages
+4–6× stronger than felt; does not tear or wrinkle
+Can be left exposed for 30–90 days during multi-stage construction
+Lighter weight — easier and faster to install
+Slip-resistant surface; better footing for roofers
Limitations
−Higher cost than felt (though often only $100–$200 difference on a full roof)
−Slippery when wet on very steep pitches with some products
Self-adhering ice-and-water shield
$0.65–$1.05 / sq ft installedIce-and-water shield is a peel-and-stick membrane made from modified bitumen with a sticky adhesive backing. It bonds directly to the wood deck and creates a completely watertight seal — including around fasteners. It is required by code at eaves in cold climates (IRC code: minimum 24 inches inside the warm wall line) and is best practice at all valleys and penetrations everywhere.
Advantages
+Seals completely around nails — prevents water intrusion at fastener holes
+Protects against ice dam backup in cold climates
+Required by code in most northern states; strongly recommended in all climates at high-risk areas
Limitations
−Most expensive option
−Not necessary as full-roof coverage in warm climates — targeted application is cost-effective
Where ice-and-water shield is required (and recommended)
| Location on roof | Cold climates (zone 5–8) | Warm climates (zone 1–4) |
|---|---|---|
| Eaves (first 3–6 ft from edge) | Required by IRC code | Best practice; not required |
| All valleys | Required | Strongly recommended |
| Around chimneys | Recommended | Recommended |
| Around skylights | Recommended | Recommended |
| Roof-to-wall transitions | Recommended | Recommended |
| Full roof coverage | High-risk zones only | Not necessary |
What to ask about underlayment in a roofing quote
What underlayment type is included?
Is it 15-lb felt, 30-lb felt, or synthetic? Most modern installs use synthetic — if a quote specifies 15-lb felt, ask why and whether an upgrade is available.
Is ice-and-water shield included at the eaves?
In northern states, this is code-required. In southern states, ask whether valleys are covered with self-adhering membrane — this is best practice everywhere.
What is the manufacturer warranty requirement?
Some shingle warranties (e.g., GAF's Golden Pledge) require specific underlayment products. Using non-approved underlayment may void the system warranty.
What is the upgrade cost for full synthetic vs. felt?
The difference on a 20-square roof is typically $200–$600. This is usually worth paying — ask for a line-item breakdown.
Frequently asked questions
What is roof underlayment and do I need it?↓
What is the best roof underlayment?↓
How much does roof underlayment cost?↓
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