*The Hempstead Living “Asso” is a one-bedroom 768 sf hemp-lime ADU with a covered porch. Photo courtesy of Root Down Designs.*

Hempcrete ADU Plans Released

By Jean Lotus

New architectural plans for three hempcrete ADU designs were released this week by a Carolinas-based team who say their multi-year experience designing and building hemp-lime homes can boost success for those who want to build with hempcrete.

The Hempstead Living designs were created by natural building architect April Magill of Charlotte, SC-based Rootdown Designs who teamed up with legendary hempcrete designer and builder Tim Callahan of Asheville, NC.

“We are trying to get high-quality architecture without the price tag of custom architecture into more people's hands,” Magill told HempBuild Mag. “We are providing attainable and accessible pathways for people because hiring a team of architects and designers is not cheap,” she added.

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Americhanvre

Texas Healthy Homes

South Bend Industrial Hemp

Sativa Building Systems

Whitefield Hemp Partners

Hemp Traders

Hillside Center for Sustainable Living

Gradek Contracting & Designs

Hempstead Living architects April Magill (L) and Tim Callahan (R)

The benefit of experience

Callahan, an early pioneer in US hempcrete construction, says the plans share winning design details from his experience “on both sides” as both a designer and a builder.

Callahan designed and built around 10 hemp-lime homes between 2009-2016 in North Carolina and Virginia, inclusing the now-famous NauHaus in Asheville. He also helped co-author the 2024 International Residential Code Appendix for Hempcrete.

“The designs are based on experience from successful projects that [builders] can use as a guide,” Callahan told HempBuildMag.

Callahan, published Building Green: A Complete How-to Guide To Alternative Building Methods with partner Clarke Snell in 2006.

Callahan’s new book, Hempsteads: Design details for successful hemp-lime construction will be published this fall.

Magill has worked as an architect and natural builder for 10 years.

“Unlike a lot of the other architects I've worked with, April has a lot of hands-on field experience, so I think there is a lot of depth in what she brings to the process,” Callahan said.

The house plans clarify details that can be confusing to contractors and building officials not familiar with the material, Magill said.

“Little framing differences are shown and called out to try to take as much guesswork and room for failure out of the equation,” she said.

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*The Nauhaus, built by Tim Callahan and partner Clarke Snell in Asheville, NC. Photo courtesy of VRBO*

Midwest Hemp Technology

Hemp Carbon Standard

United Fiber Co

Hemp Building Co

3 Designs

The three designs for the Armanca, Altair and Asso, of 308, 480 and 768 sq. ft. respectively, include architectural details perfected over multiple successful hemp-lime projects, Magill and Callahan said. All plans include kitchens and baths.

Hempsteads also offers architectural plans for larger homes up to 3,500 sq. ft.

“Bidding set” plans cost $999 for a fully detailed set of house plans, which include floor plans, a roof plan, four exterior building elevations and special details for hempcrete and window and door openings and electrical system suggestions.

Readers of HempBuild Mag receive a FREE license to build ($1,500 value) by using discount codes at checkout: ARMANCA999, ALTAIR999 and ASSO999.

The plans include a list of suggested “Healthy Home” bio-based building materials and fixtures that are currently on the market for the interior of a home. The plans also come with a pre-order for Callahan’s new book.

The company strongly suggests that owners secure financing and meet with local building code officials before ordering the plans.

*The “Altair” is a 480 sq.ft. design with front and back porches. Image courtesy of Root Down Designs*

US Hemp Building Assn.

HEMPALTA

Metaihemp

Hemp Build School Mastermind

Unique to hemp-lime homes

Some of the unique elements of the Hempstead designs include lateral (sheer) bracing with diagonal supports instead of modern customary plywood and plastic house wrap.

Properly cured hempcrete wall envelopes must maintain vapor permeability to wick moisture out of a living space, which helps discourage mold in the home.

Walls shouldn’t be covered up with non-permeable sheathing materials – which may be a surprise to local building departments. But, Magill says, diagonal bracing has been used for centuries because it works.

“There are 300-year-old buildings in historic downtown Charlotte and none of those have plywood sheathing,” Magill pointed out. “They used diagonal bracing.”

Other details unique to hempcrete building are best practices for window and door openings and areas where the wall attaches to the top plate and foundation.

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

The three Hempstead ADU designs can be modified with additional consultations with the architects, or they can be a starting point for an architect or owner to build a custom plan with proven design details that work well for hempcrete.

Homeland Hempcrete

HempStone

Complete Hemp Processing

Verdant Structural Engineers

*The “Armanca” is a 308 sq. ft. design with a porch. Image courtesy of Root Down Designs*

8th Fire Innovations

Right Coast Hemp

Tiger Fiber

Plural Office Architects

ADUs gaining popularity

As US housing costs have moved ever higher in recent years, more states and jurisdictions are allowing Accessory Dwelling Units, (ADUs) – sometimes called “granny flats”-- to help bring more housing online. In 2020, the state of California removed zoning and permitting barriers statewide to encourage the building of more than 1.5 million ADUs. Other states like Colorado and municipalities like Seattle, Portland OR and cities in Florida and Texas have followed suit. ADUs can be rented out or used as temporary housing for family members, depending on local laws.

Hemp-lime is an ideal wall infill material for ADUs because of its high performance and ability to keep electric bills low and increase indoor comfort while avoiding petrochemical-based building materials.

In 2021, Chris Velasco of San Diego built a 750 sq. foot hemp-lime ADU at a family property in Calexico, CA where summer temperatures can reach 120 degrees.

Hempcrete is a “climate resilient material,” Velasco told HempBuild Mag.

Magill and Callahan said they wanted the new ADU plans to remove barriers and streamline the process for homeowners and builders interested in building with hemp-lime.

The plans clarify elements of hemp building that might be “confusing on the job site,” Callahan said. “Being a part of lots of hempcrete builds, we’ve seen what works and what has not worked so well,” he added.