Understanding Roof Underlayment: Why It Matters in Arizona's Heat
· 9 min read
Roof underlayment is the hidden hero of your roofing system — the critical waterproofing layer between your tiles or shingles and the roof deck. In Arizona's extreme heat, underlayment works harder and degrades faster than anywhere else in the country. Understanding underlayment types, failure signs, and replacement timing can save you thousands.
What Is Roof Underlayment and Why Does It Matter?
Roof underlayment is a water-resistant or waterproof barrier material installed directly on top of the roof deck (plywood or OSB sheathing) and beneath the primary roofing material — whether that's tile, shingles, metal, or any other surface. Think of it as your roof's secondary defense system. While tiles and shingles are designed to shed the majority of water, they are not completely waterproof.…
Types of Roof Underlayment: Synthetic vs. Felt
Two main categories of underlayment are used in Arizona roofing: traditional organic felt and modern synthetic underlayment. Each has distinct characteristics that affect performance in desert conditions. Traditional felt underlayment (commonly called tar paper or roofing felt) comes in 15-pound and 30-pound weights. It is made from organic fibers (cellulose or fiberglass) saturated with asphalt. …
Self-Adhered vs. Mechanically Attached Underlayment
Beyond the felt vs. synthetic distinction, underlayment is also categorized by its attachment method: self-adhered (peel-and-stick) or mechanically attached (nailed or stapled). Self-adhered underlayment features a factory-applied adhesive backing that bonds directly to the roof deck, creating a sealed, waterproof layer with no mechanical penetrations. This is the premium option and provides the h…
How Arizona Heat Degrades Underlayment Faster
Arizona's climate creates uniquely harsh conditions for roof underlayment. The combination of extreme heat, intense UV radiation, and dramatic temperature swings degrades underlayment significantly faster than in most other states. During summer months, Phoenix roof surfaces routinely reach 150-170 degrees Fahrenheit on sunny afternoons. This heat radiates through tiles and shingles to the underla…
Frequently Asked Questions
How long does roof underlayment last in Arizona?
In Arizona's extreme heat, felt underlayment typically lasts 12-18 years under tile, while premium synthetic underlayment lasts 20-30 years. These lifespans are 30-50% shorter than in moderate climates due to sustained extreme temperatures and thermal cycling. Regular inspections after the 15-year mark are essential.
What is an underlayment-only re-roof and how much does it cost?
An underlayment-only re-roof involves carefully removing existing tiles, replacing the degraded underlayment with new material, and reinstalling the original tiles. In Arizona, this costs $3,000-$8,000 depending on roof size and complexity, and extends the life of your tiles by another 20-30 years.
Is synthetic underlayment worth the extra cost in Arizona?
Absolutely. Synthetic underlayment costs only $0.15-$0.30 per square foot more than felt but lasts 50-100% longer in Arizona's extreme heat. It resists temperatures up to 260°F, won't absorb moisture or rot, and maintains its integrity through thousands of thermal cycles. The small upfront premium saves significantly over the roof's lifetime.
How can I tell if my underlayment needs replacement?
Signs include water stains on ceilings after rain despite intact tiles, musty odors in the attic, visible brittleness or cracking when a roofer lifts tiles to inspect, and dark spots on the underside of roof decking visible from the attic. A professional inspection by Simply Roofing can assess your underlayment condition.
What type of underlayment is best for tile roofs in Phoenix?
Premium high-temperature synthetic underlayment rated for 250°F+ is the best choice for tile roofs in Phoenix. Self-adhered synthetic in valleys, eaves, and around penetrations provides the highest waterproofing protection. Simply Roofing exclusively uses premium synthetic underlayment on all tile roof installations and re-roofs.