Hempcrete Homes: What a New Zealand Guide Teaches U.S. Builders

The Highland Hemp House in Bellingham, Washington, after the hempcrete was cast and before plastering. Photo: Tommygibbons46, via Wikimedia Commons, CC BY-SA 4.0

A wall that stores carbon instead of emitting it

Every so often a material comes along that changes how we think about a wall. Hempcrete is one of them. A recent guide from Thriving Kiwi, written by Reece Clements, a chemical engineer who built his own tiny home in Hawke's Bay, walks through what it actually takes to build a hempcrete home in New Zealand: the costs, the permitting path, and who is doing the work. It's written for Kiwis, but most of the lessons travel well. Here's our take on what it means for homeowners in the U.S.

What hempcrete is (and isn't)

Hempcrete is a mix of hemp hurd (the woody inner core of the hemp stalk), a lime-based binder and water. It's packed into forms around a wood or steel frame and cures into a lightweight, insulating wall. The key point the guide makes early: hempcrete is not structural. The frame carries the loads; hempcrete is the high-performance infill that wraps around it.

That's why it pairs so naturally with timber framing, which we already champion in our Sustainable Design work. You aren't reinventing the structure. You're upgrading the wall around it.

Why builders are paying attention

• Carbon storage: hemp pulls CO₂ from the air as it grows, and the lime binder absorbs more as it cures.

• Moisture management: the walls are vapor-open, so moisture moves through them instead of getting trapped, which matters a lot for mold.

• Fire and pest resistance: lime doesn't burn, and its high alkalinity discourages insects and mold.

• Comfort: the walls have real thermal mass, which evens out indoor temperature swings.

One honest caveat: inch for inch, hempcrete insulates less than foam or fiberglass, so the walls are thick. Its performance comes from the combination of insulation, mass and breathability, not from R-value alone.

Cost: not the budget option

The guide is refreshingly candid here. It leans on the Hemp Building Association of New Zealand, which puts hempcrete roughly on par with a brick-and-block house, in the mid-to-upper range of conventional construction. The case for hempcrete isn't a cheaper build. It's lower heating and cooling bills, low maintenance and a very long service life. Owner-builder labor and retrofitting hempcrete into an existing frame are two ways people bring the cost down.

Permitting: a clearer path in the U.S.

In New Zealand, hempcrete goes through an "Alternative Solution" consent path: more documentation, an engineer's sign-off, and a council willing to review the evidence. The U.S. picture has improved. The 2024 International Residential Code added Appendix BL, Hemp-Lime (Hempcrete) Construction, which gives builders and code officials a prescriptive reference for nonstructural hemp-lime walls in homes up to two stories in low seismic-risk regions.

The catch is that an appendix only applies where a state or city adopts it. Where Appendix BL hasn't been adopted, or a project falls outside its scope, it can still be proposed to the local building official on a project-by-project basis. And in high-seismic areas like much of California, expect engineering to be part of the conversation. Either way, the first call to your building department is the most important one.

Our take

The guide's closing advice is advice we'd echo: experience the material before you commit. Visit a hempcrete build, take a hands-on workshop, and talk to people who live with it. Hempcrete isn't right for every project. It suits owners who value lifetime performance over the lowest upfront number and who are willing to put a little extra time into permitting. But for an ADU, an addition or a timber-frame retrofit, it deserves a serious look.

Thinking about natural wall systems for your next project? Contact us. We're happy to talk through whether hempcrete, or another bio-based insulation, makes sense for your home.

Source: Can I Build a Hempcrete Home in NZ? Costs, Consent and Suppliers, by Reece Clements, Thriving Kiwi.