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 "Nau 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
