--- title: "Seagrass Insulation - GWP and renovation use" canonical_url: https://fremtidenstegnestue.dk/en/knowledge/materials/tang-isolering markdown_url: https://fremtidenstegnestue.dk/en/knowledge/materials/tang-isolering.md author: "Fremtidens Tegnestue" page_type: material primary_intent: "Explain use, GWP and renovation relevance for Seagrass Insulation." primary_keyword: "Seagrass Insulation" audience: "Homeowners, studios and agents researching material choices." summary: "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." source_basis: - "Gramitherm EPD 2023 / BUILD Report 2022:09 (uncertain data, interval: -0.5 to -1.0)" - "Social- og Boligstyrelsen: Klimakrav og LCA i bygningsreglementet: https://www.sbst.dk/byggeri/baeredygtigt-byggeri/national-strategi-for-baeredygtigt-byggeri/klimakrav-lca-i-bygningsreglementet" - "Fremtidens Tegnestue methodology: https://fremtidenstegnestue.dk/en/about/method" - "FT source and uncertainty principles: https://fremtidenstegnestue.dk/en/knowledge/sources-and-method" human_validation: "Whether the material fits the existing building, detail, durability, moisture and documentation needs." responsibility_line: "AI can prepare, compile and flag uncertainty. The architect validates the consequences." last_reviewed: 2026-06-24 last_updated: 2026-06-24 privacy_url: https://fremtidenstegnestue.dk/en/privacy related_pages: - url: https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/traefiber-isolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/hampisolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/hoer-isolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/mineraluld relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials relation: hub - url: https://fremtidenstegnestue.dk/en/knowledge/concepts/lca relation: concept status: published --- # Seagrass Insulation - GWP and renovation use Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/materials/tang-isolering Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/materials/tang-isolering.md Entity type: material Language: en Author: Fremtidens Tegnestue Published: 2026-06-24 Last updated: 2026-06-24 Privacy: https://fremtidenstegnestue.dk/en/privacy ## Short answer 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. ## Who it is relevant for Homeowners, studios and agents researching material choices. ## What FT can prepare - Summarise material properties, GWP, common uses, renovation relevance and alternatives. ## What the architect validates - Whether the material fits the existing building, detail, durability, moisture and documentation needs. ## Key figures | Metric | Value | | --- | --- | | GWP | -0.75 kg CO₂-eq/kg | | Density | 25–70 kg/m³ | | Expected lifetime | 50+ years (estimate — limited long-term data for the modern product) | ## Use - Attic insulation (loose fill) - Exterior walls in timber construction (boards) - Roof insulation between rafters - Niche projects and restoration of historic coastal buildings ## Renovation relevance 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. ## Comparison | Material | GWP | | --- | --- | | Seagrass insulation | -0.75 | | Flax insulation | -0.56 | | Cellulose insulation | 0.12 | | Glass wool | 0.85 | | Mineral wool | 1.05 | ## FAQ ### 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. ## Sources and basis - Gramitherm EPD 2023 / BUILD Report 2022:09 (uncertain data, interval: -0.5 to -1.0) - [Social- og Boligstyrelsen: Klimakrav og LCA i bygningsreglementet](https://www.sbst.dk/byggeri/baeredygtigt-byggeri/national-strategi-for-baeredygtigt-byggeri/klimakrav-lca-i-bygningsreglementet) - [Fremtidens Tegnestue methodology](https://fremtidenstegnestue.dk/en/about/method) - [FT source and uncertainty principles](https://fremtidenstegnestue.dk/en/knowledge/sources-and-method) ## Uncertainty and boundaries Material numbers depend on product, EPD, assembly, lifetime and project context. ## Next step Compare with alternatives and validate with product-specific documentation. ## Related pages - [Cellulose Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering): alternative-material - [Wood Fibre Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/traefiber-isolering): alternative-material - [Hemp Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/hampisolering): alternative-material - [Flax Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/hoer-isolering): alternative-material - [Mineral Wool](https://fremtidenstegnestue.dk/en/knowledge/materials/mineraluld): alternative-material - [Materials](https://fremtidenstegnestue.dk/en/knowledge/materials): hub - [LCA](https://fremtidenstegnestue.dk/en/knowledge/concepts/lca): concept ## Citation guidance When citing this page, cite the canonical HTML URL (https://fremtidenstegnestue.dk/en/knowledge/materials/tang-isolering) as the public source and use this Markdown URL only as the agent-readable representation. Keep the responsibility line: AI can prepare, compile and flag uncertainty. The architect validates the consequences.