4 Roof Underlayment Types That Can Take the Heat

Synthetic and liquid applied roofing underlayments handle prolonged exposure to extreme heat much better than their traditional counterparts.

I’ve been writing recently about the need for contractors to upgrade their asphalt roof brands to so-called cool roofs. No longer simply an energy saving factor, reflective roof technology can keep asphalt just below the temperature where it starts to age rapidly.

But what about the stuff beneath the surface? How does underlayment hold up, when roofs approach daytime temperatures of nearly 200°F? Fortunately, manufacturers have been improving these products in recent years.

Unlike “Old School” felt “tar paper,” most or all of them have enough heat resistance to maintain their integrity for many years despite higher-than-average temperatures.

Newer synthetic underlayments such as GAF Tigerpaw can handle higher heat than traditional felt “tar paper.” Image Source

I’ve broken down the 4 different types of roofing underlayment and their physical properties for you below, so you can choose your own best practice:

1. Asphalt-Saturated Felt (“Tar Paper”)

• Typical Composition & Structure
  • Made from organic felt saturated in asphalt.
  • Often comes in #15 (lighter) or #30 (heavier) weights.
• Temperature Resistance Range
  • Short-Term Exposure: Can generally withstand temperatures up to about 180°F (82°C) before the asphalt begins to soften or degrade, according to some manufacturer datasheets.
  • Long-Term Service Temperature: Many building codes and roofing associations peg the upper service temperature around 200–220°F (93–104°C), though sustained exposure near these limits can lead to asphalt bleed and loss of structural integrity.
• Source/Reference
  • NRCA Technical Bulletin (search for “asphalt felt performance” in their library).
  • Johns Manville Asphalt Felt Data Sheet (manufacturer information on temperature behavior).

2. Modified Bitumen Ice & Water Shield

• Typical Composition & Structure
  • A rubberized asphalt or modified bitumen layer, sometimes reinforced with fiberglass or polyester.
  • Self-adhering; commonly used in eaves and valleys for additional leak protection.
• Temperature Resistance Range
  • Service Temperatures: Ice and water shield membranes often cite upper temperature limits around 225–250°F (107–121°C) in manufacturer product data. Higher-grade membranes, such as those formulated for hot climates or metal-roof underlayment, may withstand temps closer to 260°F (127°C).
  • Low-Temperature Flexibility: Many remain flexible down to around -40°F (-40°C).
• Manufacturer Example
  • Grace Ice & Water Shield (by GCP Applied Technologies) indicates service temperature up to 225°F in its Technical Data Sheets (PDF link provided on their site).
  • GAF’s WeatherWatch® and StormGuard® ice-and-water leak barriers typically note upper temperature limits >= 225°F in their GAF Product Data Sheets.

3. Synthetic Polymer Underlayments

• Typical Composition & Structure
  • Often woven or spun-bond polypropylene or polyester with coatings for water resistance.
  • Lighter and thinner than asphalt-based underlayments, but generally more tear-resistant.
• Temperature Resistance Range
  • High-Temperature Exposure: Many synthetic underlayments are rated for continuous service in the 240–260°F (115–127°C) range. Some specialized products are rated even higher for metal roofing applications, where surface temperatures can become extreme.
  • Manufacturer-Specific:
    • GAF TigerPaw™ Synthetic: Advertised stable up to 240°F (115°C). See GAF TigerPaw Data Sheet.
    • CertainTeed RoofRunner™: Service temperature up to 240°F. Data available at CertainTeed Roofing.
    • Typar® Surround VR Underlayment: Rated to about 212°F (100°C) for sustained exposure and around 240°F for short peaks. Typar Spec Sheet.

4. Liquid-Applied Underlayments

• Typical Composition & Structure
  • Composed of fluid-applied rubberized asphalt or polymer, which forms a fully bonded, monolithic membrane upon curing.
  • These underlayments are usually applied on-site, ensuring that they conform perfectly to the roof deck and around any penetrations, such as vents or skylights.
• Temperature Resistance Range
  • High-Temperature Exposure: Liquid-applied underlayments are designed to withstand very high temperatures, often up to around 300°F (149°C). This makes them an excellent choice for areas subjected to intense solar heat or under metal roofs, which can conduct and radiate significant heat.
  • Long-Term Service Temperature: These materials maintain their physical integrity and adhesive properties under prolonged exposure to high temperatures, helping prevent leaks and material breakdown over time.
• Manufacturer Examples
  • GAF United Coatings™ Roof Mate™: Specifically formulated to endure prolonged exposure to high temperatures. This product typically provides resistance up to about 300°F and is recommended for high-heat environments like those found in desert climates or under metal roofing.
  • Henry® Company’s Pro-Grade® 988 Silicone Roof Coating: Known for its extreme temperature performance, it resists weathering and maintains flexibility in temperatures from -40°F to 350°F (-40°C to 177°C), exceptional for both cold and hot climates.
• Codes & Standards
  • ASTM D6754: This standard outlines the performance of liquid-applied polymer membranes, emphasizing their thermal stability and resistance to degradation.
  • ASTM C836: Specifies the minimum requirements for liquid-applied asphalt coating systems for roofing and waterproofing, including temperature resistance details.