Water-Resistive Barrier and Underlayment


Chapter 14, section 1403.2, of the International Building Code (IBC), which addresses weather protection of exterior walls, states that “Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1405.4. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistant barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section 1405.3.”

Section 1404.2 defines a water-resistive barrier as “a minimum of one layer of No.15 asphalt felt, complying with ASTM D226 for Type 1 felt or other approved materials.”

Water-resistive barriers (WRBs), aka house wraps, include all types of synthetic materials installed over the sheathing and behind the exterior siding of a house to protect the wall assembly from the rain while still allowing water vapor to pass through to the exterior. Housewraps have become a popular replacement for asphalt felt, and NTA tests and certifies WRB materials for code compliance.

Roofing Underlayment

Chapter 15 of the International Building Code (IBC), which addresses roof assemblies and rooftop structures, defines a roof underlayment as “One or more layers of felt, sheathing paper, nonbituminous saturated felt or other approved material over which a steep-slope roof covering is applied.”Section 1507.2.3, which addresses the requirements for roof underlayments that states “Unless otherwise noted, required underlayment shall conform to ASTM D226 Type 1, ASTM D4869 Type 1, or ASTM D6757.” NTA can help! NTA can also perform ASTM E96 to test the permeability of materials for water vapor transmission.

What ICC NTA can do

ICC NTA offers a single-source solution for all testing, inspection, certification, evaluation, and follow-up services. Having all required services performed by a single vendor saves you a significant amount of time and money.

NTA is fully accredited by A2LA to the ISO 17025 (Midwest/Southwest testing laboratory), ISO 17020 (inspection body) and, ISO 17065 (certification body)  for the code compliance of WRBs and underlayments.

NTA conducts tests according to several different methods, including but not limited to:

ASTM D226: Standard Specifications for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing – this standard outlines the minimum requirements for both house wraps and underlayments, including properties such as:

ASTM D4869: Standard Specification for Asphalt-Saturated Organic Felt Underlayment Used in Steep Slope Roofing – this standard outlines the minimum requirements for underlayments, including properties such as:

  • Tear strength
  • Pliability
  • Loss of heating
  • Liquid water transmission
  • Breaking strength
  • ICC—ES AC38
  • ICC—ES AC48

ICC-ES AC38: Acceptance Criteria for Water-Resistive Barriers

ICC-ES AC48: Acceptance Criteria for Self-adhered Roof Underlayments for Use as Ice Barriers

ICC-ES AC71: Acceptance Criteria for Foam Plastic Sheathing Panels Used as Weather-resistive Barriers

ICC-ES AC382: Acceptance Criteria for Laminated Fibrous Board Sheathing Material Used as a Water-resistive Barrier

For more information about our testing house wraps or moisture barriers, contact us.

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