--- title: "Straw (Construction) - GWP and renovation use" canonical_url: https://fremtidenstegnestue.dk/en/knowledge/materials/halm markdown_url: https://fremtidenstegnestue.dk/en/knowledge/materials/halm.md author: "Fremtidens Tegnestue" page_type: material primary_intent: "Explain use, GWP and renovation relevance for Straw (Construction)." primary_keyword: "Straw (Construction)" audience: "Homeowners, studios and agents researching material choices." summary: "Straw is one of the oldest and cheapest bio-based building materials. In modern construction, pressed straw bales (typically wheat or rye straw) are used as insulation in walls, roofs and floors. Straw has a significantly negative GWP — it stores CO₂ in the structure. It requires thicker layers than conventional insulation (350–500 mm), but material cost is very low. CFBB published an approved building guide for straw construction in December 2025." source_basis: - "BUILD Report 2022:09 / Realdania (interval: -1.0 to -2.0)" - "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/hampisolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/traefiber-isolering relation: alternative-material - url: https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering 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 --- # Straw (Construction) - GWP and renovation use Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/materials/halm Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/materials/halm.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 Straw is one of the oldest and cheapest bio-based building materials. In modern construction, pressed straw bales (typically wheat or rye straw) are used as insulation in walls, roofs and floors. Straw has a significantly negative GWP — it stores CO₂ in the structure. It requires thicker layers than conventional insulation (350–500 mm), but material cost is very low. CFBB published an approved building guide for straw construction in December 2025. ## 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 | -1.5 kg CO₂-eq/kg | | Density | 80–120 kg/m³ (pressede baller) | | Expected lifetime | 100+ years (documented in historic buildings with lime plaster, BUILD Report 2022:09) | ## Use - Exterior walls (straw bale pack, 350–500 mm) - Attic insulation (loose straw or bales) - Roof insulation in new structures - Outbuildings and secondary buildings ## Renovation relevance Straw is most relevant for new builds or comprehensive renovation. For extensions or external retrofitting, straw bale packs can be used as new exterior walls — but this requires wider foundations and eaves adaptation. It is not a drop-in replacement for mineral wool in existing structures. ## Comparison | Material | GWP | | --- | --- | | Straw | -1.5 | | Hemp insulation | -1.5 | | Cellulose insulation | 0.12 | | Glass wool | 0.85 | | Mineral wool | 1.05 | ## FAQ ### Is straw fire safe? Pressed straw bales with lime render are surprisingly fire-resistant — the dense compression and render layer prevent oxygen access. Fire tests show REI 90 for rendered straw bale walls. Loose straw, however, is flammable. ### Does straw attract pests? No, not in pressed bales behind render. The dense compression and alkalinity of lime render makes the structure uninteresting to rodents and insects. ### Can straw be used in renovation? It is most suitable for new builds or comprehensive renovation where the wall structure is entirely replaced. External straw bale insulation is possible but requires new foundation detail and wider eaves. ### Is straw construction approved in Denmark? Yes. CFBB published an approved building guide for straw construction in December 2025. ## Sources and basis - BUILD Report 2022:09 / Realdania (interval: -1.0 to -2.0) - [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 - [Hemp Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/hampisolering): alternative-material - [Wood Fibre Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/traefiber-isolering): alternative-material - [Cellulose Insulation](https://fremtidenstegnestue.dk/en/knowledge/materials/celluloseisolering): 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/halm) 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.