Roof Underlayment
A water-resistant layer (felt or synthetic) installed between the roof decking and shingles to provide a secondary weather barrier.
Quick answer
Roof Underlayment: A water-resistant layer (felt or synthetic) installed between the roof decking and shingles to provide a secondary weather barrier. Typical cost: $0.15–$0.45 per sq ft installed; $300–$900 on a typical 2,000 sq ft roof..
Why it matters
Underlayment is the backup if your shingles fail. Upgrading from #15 felt to synthetic adds $200–$500 to a reroof and dramatically improves leak protection.
Typical cost
$0.15–$0.45 per sq ft installed; $300–$900 on a typical 2,000 sq ft roof.
Pros
- • Cheap insurance against shingle leaks
- • Synthetic options last decades
- • Improves wind uplift resistance
Cons
- • Felt tears easily during install
- • Often skipped or under-spec'd on cheap quotes
Common uses
- • Required base layer for all shingle and metal roofs
Alternatives
Self-adhered membrane (premium upgrade)
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Frequently asked questions
- Felt vs synthetic underlayment?
- Synthetic is lighter, tear-resistant, and lasts longer — worth the small upcharge on any reroof you plan to keep 20+ years.
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