Hempcrete is a bio-based building material made from hemp hurd (the woody inner core of the hemp stalk), a lime-based binder, and water. It's used as insulation, wall infill, and plaster in residential and commercial construction.
Unlike synthetic insulation like spray foam or fiberglass, hempcrete is carbon-storing — it absorbs more CO2 during its lifecycle than it produces. It's naturally fire-resistant, mold-resistant, and improves indoor air quality by regulating humidity and absorbing pollutants.
How Hempcrete Is Made
Traditional hempcrete combines three ingredients:
- Hemp hurd — the chopped woody core of industrial hemp stalks, providing structure and insulating air pockets
- Lime binder — natural hydraulic lime (NHL) or hydrated lime that hardens through carbonation, creating a breathable mineral matrix
- Water — activates the lime and allows mixing
GaiaCrete™ by Mr Hemp House® enhances this formula with misc pozzolans and more — creating a faster-curing material whose high-alkalinity mineral composition strongly inhibits fungal colonization.
Hempcrete R-Value
For planning purposes, hempcrete and GaiaCrete™ hemp-lime provide R-2.5+ per inch. Actual thermal performance varies by formulation, density, moisture content, installation method, and complete wall assembly.
Final whole-wall thermal performance depends on the complete assembly, including material density, framing, finishes, thermal bridging, moisture conditions, and installation — so it should be modeled by your designer rather than estimated by multiplying a per-inch figure. R-value alone also doesn't tell the full story: hempcrete's thermal mass stores and releases heat slowly, reducing temperature swings and HVAC cycling.
Hempcrete R-Value vs Common Insulation Materials
Published per-inch figures for common insulation materials, shown alongside how each behaves in a real wall. Per-inch values are manufacturer or industry planning references, not whole-wall results.
| Material | Planning R-value / inch | Typical wall thickness | Moisture behavior |
|---|---|---|---|
| Hempcrete / GaiaCrete™ hemp-lime | R-2.5+ | 10–14 in | Vapor-open, buffers humidity |
| Closed-cell spray foam | R-6.5 to R-7.0 | 2–3 in | Vapor barrier; can trap incidental moisture |
| Open-cell spray foam | R-3.5 to R-3.9 | 5–7 in | Vapor-permeable, no humidity buffering |
| Fiberglass batt | R-3.1 to R-3.8 | 3.5–6 in | Absorbs moisture, can settle |
| Mineral wool batt | R-4.0 to R-4.3 | 3.5–6 in | Water-repellent, vapor-open |
| Blown cellulose | R-3.2 to R-3.8 | 3.5–10 in | Absorbs moisture, can settle |
The practical takeaway: hempcrete needs a thicker wall to hit the same nominal R-value as foam, and it delivers that R-value as a continuous monolithic layer with no stud thermal bridging, no settling, and drying capacity in both directions. Compare full assemblies in the GaiaCrete™ vs spray foam and GaiaCrete™ vs fiberglass breakdowns.
How Much Does Hempcrete Cost?
Hempcrete pricing in 2026:
- Materials only: $50-$150+ per square foot
- Installed (GaiaCrete™ completed wall assemblies): $180–$360+ per square foot
Hempcrete Cost Compared to Conventional Insulation
Insulation is usually quoted per square foot of insulated area, while hempcrete is quoted as a completed wall assembly — that difference explains most of the sticker shock. The table below keeps the units explicit.
| Approach | Typical installed cost | What the price includes | Expected service life |
|---|---|---|---|
| Fiberglass batt | $1–$3 / sq ft | Cavity insulation only | 20–30 years |
| Blown cellulose | $1.50–$4 / sq ft | Cavity insulation only | 20–30 years |
| Closed-cell spray foam | $3–$8 / sq ft | Insulation + air/vapor control | 20–30 years |
| Hempcrete materials | $50–$150+ / sq ft | Hemp hurd, binder, delivery | 100+ year potential |
| GaiaCrete™ completed wall | $180–$360+ / sq ft | Full wall assembly, insulation, air sealing, moisture control, finish-ready surface | 100+ year potential |
Cost drivers that move a hempcrete quote the most are wall thickness, whether the material is cast in place or pre-formed, site access, crew travel, and the exterior render specification. Run your own numbers with the 100-year cost of ownership calculator.
Compared to conventional insulation, hempcrete costs more upfront. But when you factor in:
- Zero mold remediation costs (hempcrete is mold-resistant by design when properly installed)
- No replacement needed (100+ year service-life potential documented in hemp-lime research vs 20-30 years for fiberglass)
- Lower HVAC costs from thermal mass performance (varies by climate and assembly)
- No health-related costs from VOC exposure
Long-run cost depends on climate, energy prices, assembly design, and maintenance, so Mr Hemp House® does not publish a fixed payback period.
How Hempcrete Is Installed: Four Methods
Hempcrete is non-structural infill, so every method starts with a load-bearing frame — usually wood or light-gauge steel. The four approaches below differ in speed, labor, and how much curing has to happen on site.
- Cast in place (formwork). The traditional method. Temporary shuttering is set on both faces of the frame, the damp hemp-lime mix is tamped in lifts, and the forms are struck within a day or two. Best surface consistency, highest labor content, and the slowest to cure — plan 4–8 weeks before applying a finish render.
- Spray application. Wet-mix hemp-lime is pneumatically sprayed against a backing board or sheathing, then trimmed flush. Much faster on large elevations and well suited to retrofit walls with irregular substrates. Requires a trained operator and generates more waste than formwork.
- Pre-formed blocks (GaiaBloc™). Factory-cured blocks are laid up like masonry with a lime mortar. Curing has already happened off site, so the wall is finish-ready far sooner — the usual choice for occupied-home retrofits and cold-season schedules. See GaiaBloc™.
- Prefabricated panels (GaiaPanel™). Full wall sections are built and cured in a controlled facility, then craned into place. Shortest on-site schedule and the most predictable quality control, at the cost of transport logistics and less field adjustability. See GaiaPanel™.
Whichever method is used, the sequence is the same: frame and dry-in, install services, place the hemp-lime, allow the wall to cure and dry, then apply a vapor-open finish — lime render outside, lime or clay plaster inside. Do not seal a hempcrete wall with an impermeable paint or membrane; the assembly depends on being able to dry in both directions. Find a crew that has done it before through Find a Contractor.