New Book ‘Hempsteads’ Features Code-Compliant Design Details for Hemp-Lime

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Written By Jean Lotus

Hempsteads: Architectural details for hemp-lime construction by Timothy Callahan

New Book ‘Hempsteads’ Features Code-Compliant Design Details for Hemp-Lime

By Jean Lotus

A new book of architectural details for hemp-lime construction will be published in May, written by a pioneering US hempcrete builder who helped co-author the hemp-lime Appendix published for the first time in the 2024 International Residential Codes.

Asheville, NC-based Timothy Callahan’s long-awaited “Hempsteads: Architectural details for hemp-lime construction” includes code-compliant details and specifications from a career of hemp-lime and natural-building designs.

In the 2010s, before industrial hemp was even decriminalized in the 2018 Farm Bill, Callahan – then principal of Alembic Studios – designed and built about 10 hempcrete homes in North Carolina and Virginia – some of the earliest in the United States.

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Asheville, NC-based hempcrete designer/custom home builder Tim Callahan has released a new book of architectural details for successful hemp-lime construction. Photo courtesy of Tim Callahan

Hempsteads provides an overview of best practices for designing with hempcrete, including discussions of in-situ (hand packed) and spray-applied applications, structural requirements and lime binders. Callahan’s personal architectural details include designs for windows, doors, stud placement, wall bracing, electrical and plumbing rough-ins, roof and overhangs, foundations and application of lime plasters.

Callahan credited the winning design details with his experience “on both sides” as both a designer and a builder.  “The designs are based on experience from successful projects that [builders] can use as a guide,” Callahan told HempBuild Mag.  

“I have seen many people, especially in the natural building world, that have gotten into trouble,” he added. “They think, ‘oh, how hard can it be?’ But then it can lead to pretty significant failures, which can be very costly,” he added. 

Hempsteads also includes the complete International Code Council’s 2024 IRC Appendix BL and commentary. The book has an option to purchase a download library of CAD-usable design details that can be utilized (with attribution) in new projects. 

The Nauhaus in Asheville, NC, was a prototype hempcrete home designed and built by Tim Callahan and team in 2009. Photo courtesy of Tim Callahan

Well-received by US hemp building professionals

Already, others in the US hemp building industry are commenting on the book.

“Hempsteads is one of the most complete and useful texts on hempcrete construction,” wrote Cameron McIntosh, founder of Warren, PA-based Americhanvre Cast Hemp. Callahan has "truly dedicated his life to a more thoughtful approach to residential construction,” he added. 

“Tim is a true professional,” said Ray Kaderli, president of New Braunfels-based Hemp Build Network. “Having this high-level engagement from some of the original pioneers in the space is of the utmost value. This book is a ‘must-have for the library of anyone building with hemp,” he added. 

The book provides a "great overview of hemp lime construction with a great selection of architectural  details, covering different framing systems for hemp building," wrote Tim White, natural building specialist and owner of Texas Healthy Homes. 

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Apeldoorn House outside of Asheville, designed and built by Tim Callahan in 2021. Photo courtesy of Barbara Massey

High performance is unmatched

Back in the mid-2000s, Callahan said he and his colleague Clarke Snell, now based in New York, were inspired by the Architecture 2030 movement, which urged builders to design and build with materials that would have a less destructive impact on the environment.  

The two were “ridiculously idealistic” and small enough that they decided “we’re gonna do this right now. We don’t have to wait [for 2030], let’s just give this a shot,” Callahan told HempBuild Mag. Snell and Callahan co-authored Building Green: A Complete How-To Guide to Alternative Building Methods in 2009. 

But for Callahan, hemp-lime had high performance qualities that worked so well in the southeast United States, he soon found himself creating more and more projects insulated with hempcrete. 

“The truth is for most people in our region, especially because of our climate, I just don't know anything that will perform the way that hempcrete does,” Callahan said. “If you use hempcrete on exterior walls, the odds of you having any mold issues, unless you just do something really egregious, are approaching zero. That’s a big deal for people’s health,” he added. 

Callahan designed and built five houses in Asheville, including the iconic NauHaus prototype in 2009. Some of the homes were quite large and complicated.

Callahan’s largest project to date was the design/build for 9,000 sq. foot hempcrete home in Asheville. Photo courtesy of Tim Callahan

Hurricane puts hempcrete to the test

Primarily because of Callahan’s work, Asheville, NC is the hempcrete house capital of the United States. 

But the climate resilience of these structures was put to the test when Asheville was hit in late September, 2024 by the devastating Hurricane Helene. The storm destroyed homes, wiped out infrastructure in the town and killed at least 130 people. 

In a combination of luck and good design, none of the hemp houses Callahan built were damaged by the storm. Building with hemp is every bit as good in extreme rain and humidity as he suspected it would be, Callahan said. 

“From a durability standpoint [the homes] have lived up to our hopeful expectations,” Callahan told HempBuild Mag. “As to the question of resiliency, I think that was always part of the whole idea behind designing with hemp-lime in the first place,” Callahan said. “Our decision – going back 15 years –  was to reduce carbon emissions so we wouldn't have this kind of [extreme weather].” 

Architectural details shared in Hempsteads are available in CAD-friendly format in a separate downloadable digital library and may be used (with attribution) in new projects. Image courtesy of Haepenny, LLC

After a break, a return to the industry

In the early 2020s, after a 10-year flurry of designing and building hempcrete homes, Callahan almost gave up on hempcrete. He stepped away from Alembic Studios and felt discouraged about the possibility of hemp-lime scaling enough to have an impact on US construction.

 “I remember, around 2010 standing in the middle of our first boutique project, which was quite large and over-the-top, and saying, ‘we’ve learned a lot, but if we just do this one time, all this effort is wasted,” he said.  

Meanwhile, other hemp-lime builders were just getting started and sought Callahan’s expertise.

“When I began Americhanvre in 2018, I tried to connect with Tim, knowing he had some of the most complete experience regarding hempcrete construction in the US at that time,” Americhanvre’s McIntosh wrote in a message. 

It wasn’t until the two joined others in a multiyear project to co-author the IRC appendix that Callahan’s confidence returned in hempcrete’s potential to have an impact. 

Organized by then-US Hemp Building Association president Jacob Waddell, the project depended on Callahan’s invaluable expertise. The homes he designed and built were still performing well. 

A hempcrete home designed and built by Callahan in Virginia Beach, VA. Photo courtesy of Tim Callahan

A hempcrete Hempstead Living ADU design created by April Magill, AIA of Root Down Designs partnering with Tim Callahan to offer off-the-shelf hempcrete house designs. Photo courtesy of Root Down House Plans.

Making designs accessible

Today Callahan is designing hempcrete homes again and has partnered with natural builder and architect April Magill, AIA of Charleston SC’s Root Down Designs. The two designers have created off-the-shelf hempcrete house plans for ADUs and full-sized homes. 

Hempcrete adopted in Austin, TX city building codes

The hard work perfecting the IRC appendix has “opened up working with hempcrete to a lot of people,” Callahan said. 

The new IRC residential building codes still need to be adopted by state, county and local jurisdictions. But a trendsetter is the City of Austin, TX, which adopted hempcrete into the city building codes beginning July 10, 2025. 

For designers wishing to follow the new codes and learn from experienced hempcrete builders, Callahan’s new book is providing an important resource, said his old partner and co-author Clarke Snell, an Austin native who now teaches as an assistant professor of architecture at the New York Institute of Technology.

“Hempcrete is a great resource because it can deliver target thermal performance in a durable, vapor permeable, low carbon package,” Snell wrote to HempBuild Mag. “The downside is that there’s so little published professional information about how to use it.” 

Callahan’s book is filling that gap, Snell said. 

Callahan is a “master hempcrete designer/builder with many hempcrete projects under his belt. We owe him a debt for undertaking that work and sharing it with us,” Snell added.

Hempsteads: Architectural details for hemp-lime construction published by Haepenny, LLC, is available on Amazon.com and through HempBuild Magazine. 

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Jean Lotus
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