Can Roofing Felt (Underlayment) Get Wet?

Short answer: Roofing felt (underlayment) can tolerate brief exposure during installation, but on a finished roof it isn’t exposed; it’s a permanent secondary water-shedding layer beneath shingles or tile.

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What underlayment actually does

Underlayment forms a water‑shedding layer over the deck. If wind‑driven rain sneaks past shingles or tile, the underlayment directs that moisture back out to the eaves. On tile roofs—common across the Valley—the tile is the primary water‑shedding surface, while the deck‑level underlayment is the secondary protection that keeps water off the wood. Proper flashing at valleys, penetrations, and walls is critical to this system.

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“Waterproof” vs. “water‑resistant” underlayments

“Felt” (asphalt‑saturated felt) and most synthetics are water‑resistant underlayments designed to shed water beneath the finished roof; they are not the permanent outer surface. In leak‑prone spots—eaves, valleys, around skylights—roofers may add a self‑adhered leak barrier (often called “ice & water shield”) that seals around fasteners and is considered watertight; products that meet ASTM D1970 are the model here. Whether and where to use that barrier is guided by code and climate.

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Arizona conditions: monsoon bursts, UV, and high‑elevation snow

From mid‑June through September, the Arizona monsoon brings short, intense storms, strong outflow winds, and even haboobs. That’s why Behmer Roofing schedules installs to limit any temporary exposure and secures edges and laps so brief rain doesn’t become a problem. 

Northern Arizona is different. In places like Flagstaff, local amendments follow the IRC and require an ice barrier (self‑adhered membrane at the eaves) on many reroofs because ice dams can occur at elevation. That detail isn’t about Phoenix; it’s about colder high‑country roofs. Always follow your local code.

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When underlayment might get wet

On a completed roof, underlayment isn’t visible or exposed. It can encounter moisture in two scenarios:

1. During installation or a reroof. Manufacturers require installing underlayment over a dry deck, and most allow only limited temporary exposure if weather interrupts work. Some synthetics list exposure windows up to 90–180 days, but reputable roofers still cover them quickly with the final roof covering.
   
2. As a secondary defense. If a broken tile or lifted shingle lets water in, the underlayment’s job is to shed that incidental moisture and protect the deck until repair.
   

Behmer Roofing and Sheet Metal installs underlayment on a dry substrate, inspects laps and fasteners after any pop‑up shower, and replaces any damaged areas before covering—so the finished surface lies flat and the system performs as designed.

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Felt vs. synthetic: which should I expect on my home?

Both work when installed correctly:

• Felt (roofing felt/tar paper) is time‑tested and cost‑effective.
  
• Synthetics are typically lighter and more tear‑resistant and often allow longer temporary exposure windows, which can help scheduling on reroofs. Your contractor should recommend a product that meets code and the manufacturer’s installation and exposure limits for your project.
  
  

What this means for Arizona homeowners

• For shingle or tile roofs in the Valley, underlayment is a required component of the roof system, not an optional add‑on.
  
• In mountain towns, you’ll often see a self‑adhered ice barrier at the eaves by code to help stop ice‑dam back‑ups.
  
• Pro tip during storm season: if you develop a leak, a temporary roof‑leak fix can buy time, but schedule a full repair; underlayment is your second line of defense, not a permanent substitute for the surface layer.
  

Behmer Roofing plans roof installations around weather, uses underlayment and leak‑barrier combos appropriate to Arizona’s microclimates, and documents materials and details for warranty and code compliance.

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FAQ

Is roofing felt the same as underlayment?
Yes. “Roofing felt” is a common term for underlayment, especially asphalt‑saturated felt. It’s one of several underlayment types used under steep‑slope roof coverings.

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Is underlayment itself waterproof?
Standard felt and most synthetics are water‑resistant and shed water under the roof covering. For watertight protection at vulnerable areas, roofers add self‑adhered membranes that meet ASTM D1970.

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Should underlayment be exposed for long?
No. Manufacturers require a dry roof deck and limited exposure windows; pros aim to cover it fast.

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Do Arizona homes need an ice barrier?
Most Valley homes do not. In high‑elevation areas (e.g., Flagstaff), local rules often require an ice barrier at the eaves because ice dams can form there. Check your permit office.