Support NeoGAF

[EternalSunshine1976]

I've been diving deep into sustainable building options lately, especially with California's insane wildfires, earthquakes, rising energy costs, and our push toward greener construction. One material that keeps coming up as a game-changer is hempcrete (hemp-lime composite). And honestly? I think it's damn near perfect for building here in California. Let me lay out why I'm so high on it. LOL.

What even is hempcrete?

It's a mix of the woody core of the hemp plant (hurds), hydrated lime, and water. No Portland cement, no toxic additives. You cast it around a timber frame (non-load-bearing infill), spray it on, or use precast blocks/panels. It cures into a lightweight, breathable material that's basically like nature's insulation + wall system.

Why it's a fantastic fit for California

1. Fire resistance – huge for wildfiresThe lime binder makes hempcrete incredibly fire-resistant. It doesn't burn easily—in tests, walls withstand high temps (up to 1,000°F+) for hours without structural failure, often just charring or smoldering slowly with minimal smoke. In fire-prone areas like much of CA (especially after recent devastating seasons), this could be a lifesaver compared to wood-frame homes that go up like tinder. Multiple sources highlight it as a smart rebuild option post-wildfires.
2. Seismic performance – surprisingly good for earthquake countryHempcrete is lightweight (much less dense than concrete) and flexible/ductile thanks to its fibrous structure. It absorbs and dissipates seismic energy rather than cracking brittlely like traditional materials. When reinforced properly (e.g., with rebar in the frame), it performs well in shake tests and is noted for earthquake resistance. Perfect for Seismic Design Categories common in CA (though codes limit it in higher zones without engineering).
3. Climate & energy efficiencyExcellent thermal insulation (R-value around 1.5–2 per inch), high thermal mass for passive temperature regulation, and vapor-permeable so it handles moisture beautifully—no trapped condensation, mold, or rot issues (lime is naturally anti-mold/pest). In CA's diverse climates—from foggy coasts to hot Central Valley to dry deserts—it helps keep homes cool in summer, warm in winter, slashing HVAC bills and energy use.
4. Carbon-negative superstarHemp grows super fast (sequesters tons of CO₂), and the material locks that carbon away long-term. Low embodied energy in production. In a state pushing hard on emissions reductions and green building (CalGreen, etc.), this aligns perfectly.
5. Building codes are finally catching upBig news: The 2025 California Residential Code (based on IRC) includes Appendix BL for Hemp-Lime (Hempcrete) Construction! It's officially recognized for non-structural infill in one- and two-family dwellings. While adoption can vary by jurisdiction, it's now much easier to permit (no more constant "alternative materials" battles). Some areas are already approving projects, and momentum is building for wider use.

Any downsides?

Sure—it's not load-bearing on its own (needs a frame), can be more labor-intensive to install, and material/supply chains are still growing in the US (though improving fast). Initial costs might be higher than stick-frame + fiberglass, but long-term savings on energy, maintenance, fire resilience, and health (no off-gassing) make it pay off. Not ideal for super-high seismic without extra engineering, but that's true for many alternatives.


Bottom line: For new builds, ADUs, rebuilds after fires, or eco-upgrades in California—hempcrete is one of the smartest, most forward-thinking choices right now. Fire-resistant, quake-tolerant, energy-efficient, mold-free, carbon-sequestering, and increasingly code-friendly? Sign me up!


Anyone here built with it or had experience getting it permitted in CA? Would love to hear stories, tips, or resources. Let's get more hempcrete homes rising in the Golden State!

 

[Bojji]

 

[Pejo]

I love stuff like this, but it never seems to take off as far as adoption goes. I'm in no place to build right now, but thanks for making me aware that it exists.

Hope it works out well for you if you use it, OP.

 

[EternalSunshine1976]

That what I'm saying. It is perfect for California homes. It insulates like nobody's business, is completely hypoallergenic (doesn't off gas anything bad) and is an entirely biodegradable carbon sink during its use. I'm going to try to build my home out of it, if it is permitted (lol).

 

[GymWolf]

Good thing is that if your house goes in flames you are gonna be super chill while burning alive

 

[The Cockatrice]

Im sure the big bad wolf will wanna blow on my house even more now.

 

[Bojji]

Good thing is that if your house goes in flames you are gonna be super chill while burning alive

Not if you have asbestos skin!

 

[jason10mm]

This seems like the kind of thing that needs a decade or 2 of tax subsidies to get going, then it can show a distinct use case scenario.

I feel like hemp products are always "just on the cusp" of breaking, but never seem to. Fabric, paper, protein powder, this stuff.

That THC connection is a beast to shake.

 

[Mr Reasonable]

This seems like the kind of thing that needs a decade or 2 of tax subsidies to get going, then it can show a distinct use case scenario.

I feel like hemp products are always "just on the cusp" of breaking, but never seem to. Fabric, paper, protein powder, this stuff.

That THC connection is a beast to shake.

I googled and apparently, the THC isn't really in hemp. But you're right, it's 100% the association everyone makes.

I don't get it, tbh. For as long as I can remember people have been talking about Hemp as this wonder material. I saw a clip of Woody Harrelson from years ago saying all the clothes he was wearing (on the show) were made of hemp.

Is it being blocked by big Cotton (and now big concrete)?

 

[Cyberpunkd]

You guys know bricks exist, right?

 

[EternalSunshine1976]

You guys know bricks exist, right?

Bricks are a bit dangerous for entire family home builds in an active seismic area like CA. This is much more ductile and will not likely fall over and kill you.

Also, this material forms both the exterior, insulation and interior walls, and it is incredibly insulating and humidity regulating. It is better than brick in all ways, even cost.

 

[Futaleufu]

Bricks are a bit dangerous for entire family home builds in an active seismic area like CA. This is much more ductile and will not likely fall over and kill you.

Also, this material forms both the exterior, insulation and interior walls, and it is incredibly insulating and humidity regulating. It is better than brick in all ways, even cost.

Not to mention when a brick gets hot it gets really hot for a long period of time

 

[Cyberpunkd]

Bricks are a bit dangerous for entire family home builds in an active seismic area like CA.

Compare the amount of times you had an earthquake in CA with the number of fires you had.

 

[Dirk Benedict]

This seems like the kind of thing that needs a decade or 2 of tax subsidies to get going, then it can show a distinct use case scenario.

I feel like hemp products are always "just on the cusp" of breaking, but never seem to. Fabric, paper, protein powder, this stuff.

That THC connection is a beast to shake.

We have to take into account those who control materials that would be competing with this. I would guess stifling the "innovation" as much as possible. I've seen a shaker in Cigarettes, for example, fucking destroy Phillip Morris and Co. in our United States, but... then, all of a sudden? they had to exit, citing unfair competition and our Government's favoritism. I don't like or care for cigarettes, but.. it does highlight a pervasive problem in our hyper competitive, capitalistic Country.

 

[The Fartist]

Compare the amount of times you had an earthquake in CA with the number of fires you had.

It's flame resistant as well. What are you getting at?

 

[MrTroubleMaker]

It can even be made into vans

But seriously that is hopeful product. It would be nice to see it used more often.

 

[Cyberpunkd]

It's flame resistant as well. What are you getting at?

That this thread is trying to come up with a solution to the problem that already exists for hundreds of years. The thing is not about hemp - it's because American homes are designed to last just a few decades and be rebuilt by new landowners, etc., in part because of the culture and in part because probably lobbying from the construction industry. In Europe you build buildings to last.

 

[EternalSunshine1976]

That this thread is trying to come up with a solution to the problem that already exists for hundreds of years. The thing is not about hemp - it's because American homes are designed to last just a few decades and be rebuilt by new landowners, etc., in part because of the culture and in part because probably lobbying from the construction industry. In Europe you build buildings to last.

Not sure why we wouldn't want to move things forward, despite the resistance. This is a win-win for everyone if this gets more widely adopted. Just because there is a huge industry that could be disrupted, it doesn't mean we should put our heads in the sand and say fuck it. I'm an optimist, I want change, I want good things to happen for humanity. So what if things have been hard so far... things improve over time, and I'd love to participate in that change, however small, however slow, however difficult.

 

[The Fartist]

That this thread is trying to come up with a solution to the problem that already exists for hundreds of years. The thing is not about hemp - it's because American homes are designed to last just a few decades and be rebuilt by new landowners, etc., in part because of the culture and in part because probably lobbying from the construction industry. In Europe you build buildings to last.

I was just confused. Your initial argument was that, we have bricks already, then someone pointed out that bricks can be dangerous in an area that has frequent earthquakes. You then seemed to infer that there are way more fires than earthquakes in California, which is true and I understood your statement as saying that there aren't enough earthquakes to not build brick homes and that bricks are much, much more flame resistant, but hempcrete takes care of both hazards as regular bricks get extremely hot where as hempcrete resists extreme heat absorption.

 

[TDiddyLive]

A quick Google search showed why it's not in use. Basically it sucks compared to what's readily available.

8 Major Drawbacks of Hempcrete: What You Need to Know Before Building - FarmstandApp

Discover the hidden drawbacks of hempcrete construction, from slow curing times and higher costs to structural limitations. Learn why this eco-friendly building material might not be the perfect solution for your next project, despite its environmental benefits.

www.farmstandapp.com

Costs more for both product and labor. 1/20 the strength of concrete. Takes 2-3 times as long to cure. Moisture and outlying temperatures degrade it much quicker.

 

[jason10mm]

A quick Google search showed why it's not in use. Basically it sucks compared to what's readily available.

8 Major Drawbacks of Hempcrete: What You Need to Know Before Building - FarmstandApp

Discover the hidden drawbacks of hempcrete construction, from slow curing times and higher costs to structural limitations. Learn why this eco-friendly building material might not be the perfect solution for your next project, despite its environmental benefits.

www.farmstandapp.com

Costs more for both product and labor. 1/20 the strength of concrete. Takes 2-3 times as long to cure. Moisture and outlying temperatures degrade it much quicker.

Some of these limitations could probably be solved with further study and experimentation. Others, like the weather effects, are minimal in sunny california.

But without promotion or subsidies, nothing is gonna change.

 

[EternalSunshine1976]

A quick Google search showed why it's not in use. Basically it sucks compared to what's readily available.

8 Major Drawbacks of Hempcrete: What You Need to Know Before Building - FarmstandApp

Discover the hidden drawbacks of hempcrete construction, from slow curing times and higher costs to structural limitations. Learn why this eco-friendly building material might not be the perfect solution for your next project, despite its environmental benefits.

www.farmstandapp.com

Costs more for both product and labor. 1/20 the strength of concrete. Takes 2-3 times as long to cure. Moisture and outlying temperatures degrade it much quicker.

The article is a good summary of the drawbacks, and it is fair. I actually mention all of these disadvantages in my original post. Nonetheless for my specific situation, and perhaps for much of California—a non-structural infill in a timber-frame build —most of those cons don't matter.

• Hempcrete's compressive strength is indeed much lower than concrete, but in my build hempcrete does not carry loads—just insulation and enclosure in a framed structure—that's by design. Durability over centuries has been proven. There are real examples proving this, (e.g., the historic house in Miasa Village in Japan, built in 1698 and still in good condition today.
• Cost is higher now, no question—limited supply and production compared to concrete's massive industry. But as hemp cultivation grows material prices are coming down. For an owner-builder project like mine, the upfront difference gets balanced by the other advantages.
• Hemp sequesters a significant amount of CO₂ during growth, and the lime binder continues carbonating (absorbing CO₂) over decades. Concrete production is notoriously carbon-intensive. Hempcrete is legitimately carbon-negative overall—a net sink.
• In California, seismic performance matters more than raw compressive strength. Rigid concrete can fail in quakes. Hempcrete is lightweight, flexible, and it absorbs energy and reduces stress on the frame. When used as infill with a properly engineered timber or steel structure, it's considered well-suited for earthquake zones.
• It offers real upgrades over concrete: excellent thermal insulation, breathability for natural humidity regulation (prevents mold and improves indoor air quality), strong fire resistance, pest/mold resistance without chemicals, and good acoustic performance. Concrete can feel cold, prone to condensation issues, and less forgiving in variable climates.
• The longer curing time and hands-on labor? That's actually part of the appeal for me. I'll be mixing and tamping with friends and family over weekends—pizza parties, good music, community effort. It turns the "extra labor" into something enjoyable and meaningful.