Hemp-lime composite is a reasonable insulator when it is used thick enough. It is a very good humidity regulator, and in published life-cycle studies it is carbon-negative over a building’s life. Its compressive strength is only 0.2 to 1.2 megapascals, which makes it one to two orders of magnitude weaker in compression than ordinary structural concrete. It cannot hold a building up, and any account that leaves that out is selling something.
This concerns industrial hemp stalk: the woody core, or shiv, not cannabis flower. In Thailand, cannabis flower is a controlled herb dispensed on prescription form PT 33. Nothing here is engineering advice. A qualified engineer must specify building materials against local codes.
1. What It Is
Hempcrete is made from shiv (or hurd), the woody inner core of the hemp stalk that is left over after the bast fibre is stripped. The shiv is mixed with a lime-based binder and water, then cast or sprayed around a structural frame.
The name is misleading in a way that causes real confusion. Hempcrete is not concrete and it is not a substitute for concrete. It is closer to a cast-in-place insulating infill.
Cannabis literature usually points to “Isochanvre”, a French hemp-lime product, and to the claim that hemp-lime construction produces material lasting centuries. Hemp-lime building in France is real, and the technique’s modern revival did start there. But the centuries claim is based on very old lime buildings, not on modern hempcrete, which has existed for only a few decades. Treat it as an argument by analogy with lime construction, not as measured durability data.
2. The Measured Properties
Values from published building-materials research:
| Property | Measured range |
|---|---|
| Thermal conductivity | Typically about 0.065–0.12 W/m·K. Collet & Pretot (2014, Construction and Building Materials) measured 0.09–0.16 W/m·K at 23 °C and 50% RH. Conductivity rose by about 54% when density increased by two-thirds. |
| Density | Wall mixes are typically about 275–500 kg/m³. Lighter mixes are used for roof insulation and denser mixes for floors. Conductivity and strength both rise with density. |
| Compressive strength | 0.2–1.2 MPa, rising with density |
| Structural role | Non-load-bearing. Used as a low-density insulating infill around a frame |
| Moisture buffering | Moisture buffer value about 2.0–2.15 g/(m²·%RH). Collet & Pretot (2012, Construction and Building Materials) measured 2.15 for sprayed hemp concrete. Collet et al. (2013, Energy and Buildings) classed three hemp concretes as “excellent or nearly excellent” hygric regulators. |
| Carbon | Net storage of 14–35 kg CO₂-eq per square metre of wall over 100 years. The source is Pretot, Collet & Garnier (2014, Building and Environment). The study used a lime-based-binder hemp concrete wall with a thermal resistance of 2.78 m²·K/W, reported as about 26 cm thick. |
3. Reading Those Numbers Honestly
The thermal number works only because the wall is thick. Mineral wool, EPS and PIR boards sit at roughly 0.022–0.040 W/m·K. At 0.065–0.12 W/m·K, hempcrete conducts heat about 2–3 times more per centimetre. It is not in the same class as conventional insulation. Hempcrete walls perform well because they are built thick, typically 250–400 mm. At about 300 mm, a hempcrete wall reaches a U-value of roughly 0.2 W/m²·K: 0.30 m ÷ 0.07 W/m·K plus surface resistances gives about 0.22, and UK suppliers quote about 0.2. A modern insulated wall reaches a similar value with far less material. The advantage is that this is one monolithic, breathable wall fill rather than a batt or board plus membranes. The disadvantage is the floor area it takes up.
The compressive strength is the disqualifier. Structural concrete typically runs at 20–40 MPa and above. Hempcrete at 0.2–1.2 MPa is one to two orders of magnitude below that. It cannot carry a building. Every hempcrete wall is built around a timber or steel frame that does the structural work. The hemp-lime is cast around the frame as insulation and thermal mass.
This is not a defect. It is a specification. The material does an insulation job, and it does that job adequately at the right thickness. But “hemp concrete” implies structural capability the material does not have. Anyone who plans a project on the basis of the name will be disappointed at the engineering stage.
The moisture buffering is underrated and matters a great deal in this region. A moisture buffer value of about 2 g/(m²·%RH) rates good to excellent on the Nordtest scale, where “excellent” starts at 2.0. The wall absorbs humidity when indoor air is damp and releases it when the air is dry, which damps the swings. In a tropical climate this is not a footnote. It bears directly on mould, on comfort and on how hard the air conditioning has to work.
The carbon figure is real, but it has a cost side. Hemp absorbs CO₂ as it grows, and lime reabsorbs some CO₂ as it carbonates. But making lime releases CO₂ in two ways: limestone gives off CO₂ when it is calcined, and the kiln burns fuel. Curing can at most reabsorb part of the calcination CO₂, never the fuel emissions. Arrigoni et al. (2017, Journal of Cleaner Production) also found carbonation slow: after 240 days only the outer layers of hempcrete blocks had carbonated significantly. Many commercial hemp binders are formulated lime blends that include cement or pozzolanic components, which add to the binder’s footprint. Pretot et al. (2014) found binder production to be the main source of the wall’s impacts. The net 14–35 kg CO₂-eq per square metre over 100 years is a life-cycle figure, not an instantaneous one. It depends on wall thickness, binder and how the hemp was farmed and transported. For comparison, cement production accounts for around 8% of annual global CO₂ emissions (Lehne & Preston, Chatham House, 2018). The comparison favours hempcrete, and it does not need inflating.
4. Where It Actually Fits
Good candidates:
- low-rise buildings with a timber or steel frame
- walls where insulation and humidity control matter more than thinness
- retrofits of solid-wall buildings
- climates with large humidity swings
- projects with a carbon target
Bad candidates:
- anything that needs the wall itself to carry load
- below-ground or persistently wet applications
- thin walls, because the insulation value comes only with thickness
- projects where no local supply chain for hemp shiv and lime exists
That last constraint is the one that binds in Southeast Asia. Hempcrete’s carbon advantage assumes locally grown hemp. Shipping shiv across the world erases it, and the material is both bulky and light, the worst possible combination for freight costs. Hempcrete is a local material or it is nothing.
5. The Southeast Asian Question
The tropics change the calculation in both directions, and it is worth being explicit.
In favour: moisture buffering is more valuable here than in a temperate climate. The thermal performance reduces cooling load, which is where the energy goes in this region. Hemp grows fast in the right conditions, and lime construction has a long regional precedent.
Against:
- Hempcrete needs to dry properly while curing, and that is slower in high ambient humidity.
- Sustained high humidity and driving monsoon rain have to be handled by design, with overhangs, rain screens and breathable renders.
- Termites and biological attack need to be addressed, though the high-pH lime binder is a real advantage there.
- We are not aware of any publicly documented commercial supply chain for construction-grade shiv in the region.
Thailand does have a hemp-fibre base. The Highland Research and Development Institute (HRDI), which supports the Royal Project’s highland work, has developed low-THC fibre varieties, and Hmong communities in the north have a long tradition of hemp-fibre production. Whether that base can supply construction-grade shiv in useful volumes has not been publicly documented.
So the realistic near-term question in Thailand is not whether hempcrete performs. It is whether anyone can source the shiv. That is a hemp-cultivation and hemp-processing question before it is a building question, and hemp textiles face the same bottleneck.
6. The Regulatory Frame
Hemp stalk and shiv are industrial materials and sit outside the controlled-herb framework that governs cannabis flower. In Thailand:
- Flower is a controlled herb under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis) B.E. 2568, issued 26 June 2025. It may be dispensed only on prescription form PT 33.
- Extracts above 0.2% THC by weight remain Category 5 narcotics under the Notification of the Ministry of Public Health Re: Specification of Category 5 Narcotics B.E. 2565 (2022), in force since 9 June 2022. A separate Ministerial Regulation B.E. 2569, in force 26 April 2026, tightened licensing for cannabis and hemp extracts. It does not create the Category 5 status.
- Stalk, shiv and fibre are no longer listed as narcotics. Check current registration or permit requirements for cultivation and processing with the Thai FDA and the Department of Agriculture.
The Cannabis Control Act is still a draft. The Cabinet approved it on 22 September 2026, and it is now with the House. If it is enacted, it may change how hemp is regulated. Anyone planning fibre and shiv cultivation should verify the current position before investing. Building materials must also comply with Thai building codes and any relevant product standards.
If anyone in the region has built with hemp-lime, or has tried to source construction-grade shiv in Thailand or Vietnam, what did you find, and at what price? The material science is settled enough. The supply chain is the open question, and we have not found any public mapping of it.
General information, not engineering or legal advice. Specify building materials with a qualified engineer.