Hempcrete (Hemp-Lime) — FarmPal

A biocomposite of hemp hurd (woody core of hemp stalk) mixed with lime binder and water. Cast in forms or sprayed around a structural frame. Hempcrete is carbon-negative it sequesters more CO2 than its production emits.

History

Modern hempcrete developed in France in the 1980s. Now widely used in Europe with growing adoption in North America since the 2018 Farm Bill legalized hemp cultivation.

Cost/sq ft
$25-$60
Build Time
8-20 weeks
Crew Size
3-8 people
DIY Friendly
Yes ✓
Code Compliance
moderate
Thermal Mass
medium
R-Value
R-2 to R-3 per inch (R-20-30 for typical 12" wall)
Lifespan
300+ years (lime petrifies over centuries)

Best Climates

temperate
humid
cold
marine

Resistance Ratings (1-5)

tornado★★★☆☆
hurricane★★★☆☆
earthquake★★★★☆
fire★★★★☆
flood★★☆☆☆
mold★★★★★
termites★★★★★
bullets★★☆☆☆

Materials

Hemp hurd/shiv
Hydraulic lime binder (NHL 3.5 or 5)
Water
Structural timber frame
Temporary formwork
Lime plaster/render

Build Steps

  1. 1Build structural timber frame (hempcrete is non-structural)
  2. 2Install temporary formwork on one side of frame
  3. 3Mix hemp hurd with lime binder and water in mixer
  4. 4Pack hempcrete into forms around structural frame in 12" lifts
  5. 5Tamp lightly do NOT over-compact (air content provides insulation)
  6. 6Remove forms after 24-48 hours
  7. 7Allow 4-8 weeks drying time before finishing
  8. 8Apply lime render/plaster to exterior and interior
  9. 9Hemp-lime continues to petrify and strengthen over decades

✓ Pros

  • •Carbon negative
  • •Mold/pest proof
  • •Excellent moisture regulation
  • •Good insulation
  • •Breathable walls
  • •Grows stronger over centuries
  • •Fire resistant

✗ Cons

  • •Not structural
  • •Long drying time
  • •Material sourcing challenges
  • •Higher cost than some earth methods
  • •Relatively new in North America

⚠️ Warnings

  • •NOT structural always requires a timber frame
  • •Long drying time (4-8 weeks) plan for weather protection
  • •Hemp hurd supply may be limited in some regions
  • •Must use hydraulic lime (NHL), not Portland cement or garden lime
  • •Protect from rain during curing period