I was recently reviewing the 2024 International Residential Code (IRC), specifically Chapter 7 on water-resistive barriers, and noticed there have been a few changes from the 2021 version of the code. I thought this might be a good time to go over those changes, and as long as we are discussing this section of code, we’ll dive into the three ASTM standards and tests listed in R703.2. These ASTM requirements have been in the code for a long time, but some may be unfamiliar with the requirements of the products used as a WRB.

R703.2 Water-resistive barrier

This is the code language covering WRBs. The sections in red are the changes or additions from the 2021 IRC.

Not fewer than one layer of water-restive barrier shall be applied over studs or sheathing of all exterior walls with flashing as indicated in Section R703.4, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer and behind deck ledgers. The water-resistive barrier material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section R703.1. Where the water-resistive barrier also functions as a component of a continuous air barrier, the water-resistive barrier shall be installed as an air barrier in accordance with Section N1102.5.1.1. Water-resistive barrier materials shall comply with one of the following:

1. 15 felt complying with ASTM D226, Type 1.
2. ASTM E2556, Type 1 or 2.
3. Foam plastic insulating sheathing water-resistive barrier systems complying with Section R703.1.1 and installed in accordance with the manufacturer’s installation instructions.
4. ASTM E331 in accordance with Section R703.1.1
5. Other approved materials in accordance with the manufacturer’s installation instructions.

No. 15 Asphalt felt and water-resistive barriers complying with ASTM E2556 shall be applied horizontally, with…