COMPANY NAME HALM GmbH
COUNTRY Germany
SECTOR Construction
CIRCULAR BUSINESS MODEL Circular design; Product as a Service (Circularity-as-a-Service); Product life extension; Recovery and recycling
CHALLENGE
The company tackles the challenge of making an already sustainable prefabricated building system fully circular. Although its building envelopes use renewable materials such as timber, straw, and clay, they still contain steel, plastics, adhesives, sealing tapes, and other components that hinder dismantling, material separation, reuse, and recycling. HALM therefore aims to reduce these hard-to-recycle materials, simplify construction, preserve material value, minimize waste and costs, and develop slimmer circular panels for the serial energy refurbishment of existing buildings
SOLUTION
HALM offers prefabricated building envelopes made from timber, straw insulation, and clay plaster. Its solution combines an improved SB34 panel for new buildings with a slimmer SB24 panel for the serial energy refurbishment of existing buildings. The SB24 panel uses open straw, pressed directly onto existing masonry. To make its building system more circular, the company uses regionally sourced straw tied with sisal instead of synthetic twine, replaces plastic sealing tapes with sheep’s wool, and improves joints and connections using solutions such as wooden nails, hardwood or beech dowels, and CNC-machined joints. These measures reduce the use of metal, plastic, adhesives, timber, and other hard-to-recycle materials, making the buildings easier to dismantle, reuse, or recycle while also lowering material use, waste, and costs.
CIRCULAR ECONOMY STRATEGIES/BUSINESS MODEL IMPLEMENTED
By implementing circular product design through a systematical redesign of its prefabricated building envelopes to reduce hard-to-recycle materials, enable dismantling, reuse, or recycling with minimal waste, HALM puts a circular business model into practise. They reviewed their wall, roof, and floor systems, conducted life cycle assessments of the SB34 and SB24 modules to identify major emission drivers, and tested alternatives such as wooden nails, hardwood and beech dowels, sheep’s wool insulation, ESB boards, and CNC-machined joints. The company then validated these solutions through prototypes, real-building pilot projects, manufacturing feedback, and on-site testing. Circular design is embedded in its operations through regional straw sourcing, in-house straw pressing, sisal bale ties instead of synthetic twine, sheep’s wool instead of plastic sealing tapes, and connections that use less metal, timber, and material overall. It supports these technical changes with cost-benefit analysis, collaboration with receptive customers, suppliers, and partners, and continued development of circular renovation modules and regional uses for residual straw and wood.
IMPACT
Environmental Impact
Carbon sequestration quantified: The LCA established that both panels are net carbon sinks — the SB34 sequesters 62.18 kg CO₂e/m², the SB24 43.74 kg CO₂e/m² (cradle-to-gate). A reference house with a 204 m² SB34 facade stores ~12.7 tonnes of CO₂e in its walls; the Tentzerow retrofit facade (~120 m² SB24) stores ~5.25 tonnes.
Fossil emissions reduced by up to 4.79 kg CO₂e/m² through three substitution levers: regionalised straw sourcing (2.39 kg — the largest lever), metal-free connectors (2.07 kg), and sheep’s wool instead of PU tape (0.33 kg).
End-of-life circularity proven: The disassembly test (March 2026) confirmed single-variety material recovery — structural timber and cladding boards are directly reusable, clay plaster recoverable after re-wetting, and overall bio-based recovery is ~70–80% by mass. PU tape was eliminated from the joint detail.
Scaling potential: At 1% share of the German serial refurbishment market by 2030, the cumulative CO₂ benefit versus mineral-wool retrofitting is estimated at ~3 million tonnes over 2025–2050.
Social Impact
First of its kind: BV Tentzerow became the first serially prefabricated straw-insulated refurbishment building in Germany — a flagship proof that serial energy refurbishment can be done with local, renewable materials (contribution to SDG 12).
Stakeholder engagement: Feedback was collected from production staff, site managers, clients, architects and housing developers; the Tentzerow site manager called the switch to sheep’s wool a “game changer” for on-site handling.
Advancing mainstreaming of straw as a locally available, renewable building material.
Economic impact
New market segment entered (SDG 8): The SB24 retrofit panel opens the German serial refurbishment market — three commercial pilot projects completed or underway, with a product pipeline and partner network established.
Direct cost savings: The hardwood dowel element joint saves ~€14.60/lm (~65%) versus the step joint; sheep’s wool is effectively cost-neutral (+€0.09–0.19/lm); the SB24 reaches KfW Efficiency House 55 level (U-value ~0.19 W/m²K).
Premium positioning & supply chain: A new circular product line with premium positioning; EOL material recovery retains commercial value in reusable timber and cladding; HALM’s own straw-bale press ends the ~950 km logistics dependency, moving to regional sourcing (<50 km) and reducing input costs.
KEY TAKEAWAY
“Our entire team enjoyed the opportunity to re-evaluate our product and make it more sustainable.”