Straw (Construction).
Straw is an agricultural residue that would otherwise be ploughed under or burned. By building with it, the carbon is stored in the structure instead. GWP: -1.0 to -2.0 kg CO₂-eq/kg. Combined with the low material cost, straw is one of the most climate-friendly building options — but requires specialist knowledge.
- Carbon Footprint (GWP)
- −1.5 kg CO₂-eq/kg
- Density
- 80–120 kg/m³ (pressede baller)
- Expected Lifespan
- 100+ år (dokumenteret i historiske bygninger med kalkpuds, BUILD Rapport 2022:09)
Source: BUILD Rapport 2022:09 / Realdania (interval: -1.0 til -2.0)
What is straw (construction)?
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.
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 (straw bale pack, 350–500 mm)
- check_circle Attic insulation (loose straw or bales)
- check_circle Roof insulation in new structures
- check_circle Outbuildings and secondary buildings
In Renovation
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.
Questions about straw (construction)
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.
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