Ep. 8 Navigating the New Hempcrete Building Codes with Tim Callahan (IRC Appendix BL)

In this episode of the Hemp Build Podcast, host Ray Kaderli is joined by Tim Callahan of Callahan Home Designs to discuss the landmark inclusion of hemp-lime (hempcrete) into the International Residential Code (IRC).

Tim, a co-author of Appendix BL and a pioneer in the US hemp building movement, shares over 30 years of design-build experience. We take a deep dive into the technical evolution of hempcrete—from the high-labor "Now House" prototype in 2008 to the standardized, code-approved wall assemblies used today.

In this episode, you’ll learn:

• The Four Approved Wall Assemblies: Understanding interior, center, exterior, and double-stud configurations under Appendix BL .

• Fire & Safety Standards: How hempcrete achieved a 1-hour fire rating (ASTM E119) and its zero flame-spread index .

• Building Science: Why "breathability" (vapor permeability) is essential and why you should NEVER use a vapor barrier with hemp-lime.

• Code Adoption: How to work with local building officials and navigate the "snowball effect" of national code adoption .

Whether you are an architect, builder, or sustainable living enthusiast, this episode provides the technical roadmap for bringing hemp-lime into mainstream construction .

Resources Mentioned:

• IRC Appendix BL (Hemp-Lime Construction)

• Callahan Home Designs (Asheville, NC)

• The "Now House" Prototype

#Hempcrete #SustainableBuilding #IRCAppendixBL #GreenArchitecture #HempBuildPodcast #BuildingScience