TRI-FLEX® XT synthetic roofing underlayment is a high performance water-shedding underlayment. The new coating formulation provides superior foot traction. It is 20 times stronger than #30 felt and withstands high wind conditions; it is lighter than #30 felt and covers more area. The product is mechanically attached to the roof and can be used alone or in conjunction with GCP self-adhered underlayments.

TRI-FLEX® XT roofing underlayment provides a stable base for the application of mechanically-attached roof coverings and serves as a secondary water shed to help prevent leaks if water penetrates the primary roof covering. The product may also be used to temporarily “dry in” the structure for a period of 6 months before the roof construction is finished or if the primary roof coverings become damaged.

TRI-FLEX® XT underlayment is suitable for application as part of all major roof covering systems.

Product Description

TRI-FLEX® XT underlayment is a high strength woven synthetic roofing underlayment coated on both sides with slip resistant polymers. The new and improved coating formulation provides superior foot traction. This composition creates a tough, weather-resistant membrane designed to perform in the harshest conditions in North America.

TRI-FLEX® XT roofing underlayment is available in 10 sq rolls (48 in. wide x 250 ft long), and is available in with a black or gray topside surface.

Features & Benefits

Below are some of the major benefits of TRI-FLEX® XT roofing underlayment:

Improved Slip Resistant Surface - New coating provides superior foot traction

It’s lighter and covers more area - A roll of underlayment is around half the weight of #30 felt, and has nearly 5 times the coverage.

It’s stronger - TRI-FLEX® XT roofing underlayment is 20 times stronger than felt and won’t tear away from nails even in high winds.

It’s more durable - TRI-FLEX® XT underlayment can be left exposed for up to 6 months. It doesn’t dry out or rot at high temperatures. It doesn’t crack or become brittle at low temperatures.

Facilitates faster and easier installation - The lighter rolls make the one-person application fast and easy. It also means fewer trips up the ladder and lower labor costs.

Suitable for use under all major roof coverings - TRI-FLEX® XT mechanically-attached underlayment can be used under shingles, tiles, slate, metal and cedar shakes. Refer to subsequent sections for more details.

Custom Logo Available - The product can printed with a customer logo. Minimum order amounts apply. Please contact the GCP sales representative for details.

GCP technical support - TRI-FLEX® XT underlayment is backed by a team of local technical support personnel that help ensure every application goes smoothly

Product Advantages

  • Improved Slip Resistant Coating
  • Lighter and covers more area
  • Stronger and more durable
  • Facilitates faster and easier installation
  • Suitable for use under all major roof coverings
  • Custom Logo Printing Available
  • 25 Year Warranty

Installation Guidelines

  1. The roof deck must be swept clean and be smooth and dry before installation begins.
  2. TRI-FLEX® XT membrane is laid horizontally (parallel to eave), starting at the bottom of the roof, with printed side up and with 4-inch side laps and 6-inch end laps. Side laps run with the flow of water in a shingling manner.
  3. TRI-FLEX® XT underlayment should not be used at slopes less than 2:12, provided the slope is also acceptable to the primary roof covering. On slopes of less than 4:12, GCP membrane should be half-lapped a full 24 inches over the underlying course, shingle style.
  4. TRI-FLEX® XT underlayment is attached to the roof with roofing nails or staples both having 1-inch diameter plastic/metal caps, spaced at 8 inches on center (oc) on both side and end laps in normal wind zones. In high wind zones or coastal applications, double the fastening to 4 inches oc. In all cases fasten at 24 inches oc down the middle of the roll in the field of the roof. Fasteners may be hand or machine applied. Staples without caps cannot be used.
  5. Where seams or joints require sealant or adhesive, use a high quality, low solvent, asbestos free plastic roofing cement meeting ASTM D4586 Type 1, Federal Spec SS-153 Type 1 (Asbestos Free). Consult your local GCP representative for more details.
  6. Install drip edge at eaves under underlayment and at rake over underlayment.
  7. Installation of the roof covering can proceed immediately following underlayment application. TRI-FLEX® XT underlayment cannot be used as a primary roof covering. The product is not designed for permanent outdoor exposure. The installation of the final roof covering should take place within 6 months.
  8. For additional protection lay a single length of TRI-FLEX® XT membrane vertically in valleys and on hips prior to installing metal flashings (if used) and before installing horizontal underlayment. Return TRI-FLEX® XT roofing underlayment up all abutments at least 12 inches (more in heavy snow areas). Secure and trim to suit.
  9. Prior to loading roofing materials on TRI-FLEX® XT underlayment it is recommended that roof jacks, toe-boards or a storage platform be secured to the underlying roof deck to prevent slippage of stored materials on steep sloped roofs. See OSHA Regulations (Standards – 29 CFR), Fall Protection Systems Criteria and Practices – 1926.502.
  10. Check local building code to ensure compliance in your area, as local building codes may vary.

Code Approvals

  • Meets the requirements of ICC AC-188 (Acceptance Criteria for Roofing Underlayments) and Miami Dade County requirements
  • Complies with ASTM E108/UL 790 for use in the installation of Class A asphalt glass fiber mat shingles and Class C asphalt organic felt or metal shingles
  • Meets ASTM D226 physical requirements of Type I and Type II (#15 and #30 asphalt felt)

Precautions and Limitations

  • Consistent with good roofing practice, always wear fall protection when working on a roof deck.
  • Slippery when wet or covered by frost, debris or dust.
  • Do not fold over the roof edge unless the edge is protected by a drip edge, gutter or other flashing material.
  • Check with the manufacturer of the metal roofing system for any special requirements when used under metal roofing. Do not install directly under roof coverings especially sensitive to corrosion, such as zinc, without providing proper ventilation.
  • Do not install under copper, Cor-Ten®, or zinc metal roofing in high altitudes or in the desert southwest. These roofs can reach extremely high temperatures due to the low reflectivity, high absorption, and high conductivity of the metals.
  • Provide proper roof insulation and ventilation to help reduce ice dams and to minimize condensation.
  • Repair holes, fishmouths, tears and damage to product. TRI-FLEX® XT underlayment does not self-seal open fastener penetrations.
  • Do not use un-capped staples.
  • Do not install fasteners through the product over unsupported areas of the structural deck, such as over the joints between adjacent structural panels.
  • Do not stretch TRI-FLEX® XT membrane during installation. The product should be pulled taut, but should not be stretched.

Product Data 

  10 SQ ROLL
Roll length 250 ft (76.2 m)
Roll width 48 in (1.05 m)
Roll size 1,000 ft2 (92.9 m2)
Roll weight 28 lbs (12.7 kg)
Rolls per pallet 30

Performance Properties

PROPERTY TRI-FLEX® XT TEST METHOD
Color (front/back) Black/Black or Gray/Black  
Weight 28 lbs (10 sq roll)  
Tear strength MD 58 lbs; CD 77 lbs ASTM D4533
Accelerated aging Pass (no damage, cracking, chipping) ICC-ES AC48
Ultraviolet resistance Pass (no peeling, chipping, cracking, flaking) ICC-ES AC48
Water ponding Pass (no percolation) ASTM D779
Pliability Pass (no cracks) ASTM D226
Water transmission Pass ASTM D4869
Tensile strength MD 96 lbs; CD 116 lbs ASTM D828
Thickness 7 mils ASTM D3767