Underlayment is the waterproof membrane between your roof deck and your shingles or tiles. It's the actual barrier keeping water out — the surface layer just protects it from UV and impact.
The Three Underlayment Types
30# Felt (Asphalt-Saturated Paper)
The old standard. Cheap, but brittles in Arizona heat after 15–20 years. We don't recommend it on AZ tile installs anymore.
Synthetic Underlayment
Polypropylene or polyester. UV-stable, lighter, tear-resistant. Lasts 25–30 years. Our default for shingle installs.
Self-Adhered (Peel & Stick)
Rubberized asphalt with adhesive backing. Self-seals around nail penetrations. Highest performance and what we use under tile in Phoenix.
On a tile roof, the tile lasts 50+ years — but the underlayment underneath fails in 20–25. That's when 'leaks' start.
Why It's the Real Waterproofing
Shingles and tiles are designed to shed water, not seal it out. The underlayment is the actual moisture barrier. When it fails, leaks follow — even with perfect-looking shingles above.
What to Demand on Your Estimate
- ›Brand name and weight (e.g., GAF FeltBuster, Tiger Paw)
- ›Synthetic or self-adhered — never 30# felt for tile in AZ
- ›Ice & water shield in valleys and around penetrations
