Seagrass Insulation.
Seagrass insulation has an estimated GWP of -0.5 to -1.0 kg CO₂-eq/kg — but data is uncertain, and the climate impact of transport from France is significant. In a Danish scenario, the climate benefit may be less than the EPD indicates (BUILD Report 2022:09). Read the numbers together with function, lifespan, detailing and the specific building element.
- Carbon Footprint (GWP)
- −0.75 kg CO₂-eq/kg
- Source: Gramitherm EPD 2023 / BUILD Report 2022:09 (uncertain data, interval: -0.5 to -1.0)
- Density
- 25–70 kg/m³
- Expected Lifespan
- 50+ years (estimate — limited long-term data for the modern product)
How to use this assessment
The assessment of seagrass 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 seagrass insulation?
Seagrass insulation is made from eelgrass or seaweed — marine plants that are dried and processed into insulation boards or loose fill. Historically, seaweed has been used as insulation in Danish coastal houses (seaweed houses on Læsø). In modern production, Gramitherm (France) is the best-known manufacturer, producing insulation boards from roadside grass and seaweed. The product is still rare in Denmark but documented via EPD from 2023.
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 Attic insulation (loose fill)
- check_circle Exterior walls in timber construction (boards)
- check_circle Roof insulation between rafters
- check_circle Niche projects and restoration of historic coastal buildings
In Renovation
Seagrass insulation is primarily relevant as a niche product — for restoration of historic coastal buildings, demonstration projects and builders with particular interest in marine bio-resources. It is not a mainstream renovation product in Denmark currently, and availability is limited.
Questions about seagrass insulation
Can you buy seagrass insulation in Denmark?
It is difficult. Gramitherm produces in France and there is no Danish distributor as of 2026. Loose seaweed for insulation can in principle be collected locally, but it is not a standard product.
Is this the same as the Læsø seaweed houses?
Historically yes — both use eelgrass. But the Læsø houses use loose dried seaweed in thick layers on the roof, while modern seagrass insulation (Gramitherm) is industrially processed into boards.
Does seagrass insulation smell?
Dried seaweed has a faint, salty scent that disappears when built in. There are no chemical emissions.
How reliable is the GWP data?
GWP data for seagrass insulation is uncertain. Gramitherm's 2023 EPD is the primary source, but BUILD Report 2022:09 notes that transport impact is significant and the Danish scenario differs from the French.
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