Hemp Insulation.
Hemp insulation is carbon-storing — the plant absorbs more CO₂ during growth than is used in production. With a GWP of -1.5 to -1.8 kg CO₂-eq/kg, it is one of the most climate-friendly insulation materials. For comparison: mineral wool emits approx. 1.05 kg CO₂-eq/kg. Read the numbers together with function, lifespan, detailing and the specific building element.
- Carbon Footprint (GWP)
- −1.5 kg CO₂-eq/kg
- Source: BUILD Report 2022:09 / Realdania (interval: -1.5 to -1.8)
- Density
- 25–50 kg/m³
- Expected Lifespan
- 50+ years (when correctly installed in a vapour-permeable construction)
How to use this assessment
The assessment of hemp insulation is a first decision basis. Carbon numbers, density and lifespan give a point of comparison, but the material must always be read together with structure, moisture, fire requirements, detailing, maintenance and the condition of the existing building. A good material choice is therefore both a data question and an architectural judgement. The useful next step is to clarify which questions should be examined further before the material is specified in a project.
What is hemp insulation?
Hemp insulation is made from industrial hemp — a fast-growing annual crop that absorbs large amounts of CO₂ during growth. The fibres are typically bound with polyester or bicofibre and formed into batts or loose fill. Hemp insulation is vapour-permeable, carbon-storing and well suited to diffusion-open structures in older buildings. It is one of the most documented bio-based insulation materials in Danish construction research.
Carbon Footprint Compared
Negative carbon footprint (green) indicates carbon storage. Data based on EPD averages from ECO Platform and estimates per EN 15804.
Typical Applications
- check_circle Exterior walls in vapour-open construction
- check_circle Attic insulation (batts or loose fill)
- check_circle Roof insulation between rafters
- check_circle Partition walls (sound insulation)
In Renovation
Hemp insulation is ideal for renovation of older masonry and half-timbered houses where the structure is vapour-open. It suits exterior walls with lime render, attic structures with exposed rafters, and roofs with diffusion-open underlay. Avoid combining with plastic vapour barriers.
Questions about hemp insulation
Is hemp insulation fire safe?
Hemp insulation is treated with borates and meets European fire standards (Euroclass E). Behind non-combustible cladding (plaster, lime), the fire risk is comparable to mineral wool.
Can hemp insulation be used in a 1960s house?
Yes, if the construction is or can be made vapour-open. It works well in exterior walls with lime render and timber framing — but requires replacing any plastic vapour barrier with a variable sd-value vapour retarder.
Does hemp attract pests?
No. The borate treatment makes the material uninteresting to insects and rodents. There are no documented pest problems with correctly installed hemp insulation in Denmark.
What is the difference between hemp and flax insulation?
Both are plant-based and vapour-permeable. Hemp has a slightly higher lambda value (0.038-0.042 vs. 0.036-0.040 for flax), but hemp has a more negative CO₂ footprint and is typically cheaper. Both require vapour-open structures.
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