All glossary terms
Materials
Roofing Underlayment
Definition: Underlayment is the water-resistant or waterproof layer installed directly on the roof deck, under the shingles. Synthetic underlayment is now standard; older homes used felt paper.
Roofing underlayment is the secondary barrier between your shingles and your roof deck. If wind drives rain under a shingle (or if the shingle lifts in a storm), the underlayment is what keeps water out of your attic. Get it wrong and you're paying for a new ceiling.
The three main types in 2026:
**Synthetic underlayment.** Now the default on most quality installs. Polypropylene-based, lighter than felt, far more tear-resistant, walkable in wet conditions, and lasts 20+ years even if exposed. Costs $40-$80 per roll (covers ~10 squares).
**Felt paper (30# or 15#).** The traditional option. Cheap but tears easily, absorbs water if left exposed, and degrades faster than synthetic. Still common on budget installs and short-term roof-overs. Costs $20-$40 per roll.
**Ice-and-water shield.** Self-adhered, fully waterproof membrane. Required by code along eaves and valleys in any climate with freezing temperatures. Premium installs extend it 3-6 feet into the field on north-facing slopes for added ice-dam protection. Costs $80-$150 per roll.
For estimating: underlayment is a per-square line item that varies by material type and code requirements. Most pricing tools (including SatelliteQuotes) let you set a default underlayment per material and adjust per job. Always quote ice-and-water shield as a separate line in cold climates — it's the upgrade most commonly skipped to hit a lower bid, and the one that causes the most callbacks.