Embodied Carbon of Curtain Walls: Data, EPDs & Reduction Levers
Material extraction and fabrication generate 2,000–3,500 tonnes of CO2e for a 40,000 m2 curtain wall before the building is occupied, and aluminum, glass and steel account for over 90 percent of that total. This page publishes the underlying intensity figures, a worked reduction case, and the EPD framework that makes the numbers verifiable.
The three materials that dominate facade carbon
While operational carbon dominates over a 50-year building lifecycle, embodied carbon is paid upfront and cannot be recovered. The table below lists the intensity ranges Hanart uses in project-level life-cycle assessment, consistent with EPD data to ISO 14025 / EN 15804.
| Material | Embodied carbon | What drives the range |
|---|---|---|
| Primary aluminum (Hall-Heroult) | 8–16 kg CO2e per kg | Electricity source of the smelter |
| Hydro-powered aluminum | 4–6 kg CO2e per kg | Iceland, Norway, Quebec smelters |
| Coal-powered aluminum | 12–16 kg CO2e per kg | China, India grid mix |
| Recycled aluminum | 0.5–1.5 kg CO2e per kg | Remelting uses ~5% of primary energy |
| Float glass | 1.1–1.3 kg CO2e per kg | Natural gas melting furnace |
| Structural steel | 1.8–2.3 kg CO2e per kg | Brackets, anchors, reinforcement |
A 40,000 m2 unitized project: from 8,640 to 3,240 tonnes
A unitized curtain wall frame weighs roughly 18 kg per square metre of facade area, so a 40,000 m2 project uses about 720 tonnes of aluminum. At 12 kg CO2e per kg for primary aluminum, that is 8,640 tonnes CO2e. Substituting 75 percent recycled content cuts the framing carbon to 3,240 tonnes — a saving of 5,400 tonnes CO2e, approximately equivalent to removing 1,170 passenger vehicles from the road for one year.
Glass adds a comparable block: 28,000 m2 of glazing at 25 kg per square metre is 700 tonnes of glass, equivalent to 770–910 tonnes CO2e at 1.1–1.3 kg CO2e per kg. Low-E coating adds 5–8 percent, lamination 10–15 percent and heat strengthening 8–12 percent. Structural steel for brackets and anchors at 4–6 kg per square metre generates 290–550 tonnes CO2e on the same project, before galvanising adds 0.3–0.5 kg per kg for corrosion resistance.
Two levers move these numbers fastest: recycled-content aluminum in framing (0.5–1.5 versus 8–16 kg CO2e per kg) and mass reduction through value-engineered sections — every kilogram removed is a kilogram that never enters the supply chain. Both levers are available without changing the architectural envelope.
Making carbon auditable: EPDs and LEED v4.1
Environmental Product Declarations, prepared to ISO 14025 and EN 15804, give third-party verified lifecycle data for facade materials. Under LEED v4.1, the Materials & Resources credit “Building Product Disclosure and Optimization — Environmental Product Declarations” awards 1 point for using 20 products from 5 different manufacturers with EPDs, and a further point for products demonstrating optimization below industry average. The “Sourcing of Raw Materials” credit rewards recycled content directly — specifying 75 percent recycled aluminum in framing contributes to it.
Hanart requires EPD documentation from all primary material suppliers and can provide aggregated facade assembly EPDs on request. This is the same documentation carried in our project packages, so the numbers on this page are what the factory and supply chain actually report, not catalogue averages.
Embodied carbon questions, answered with numbers
For a 40,000 m2 project, material extraction and fabrication typically generate 2,000–3,500 tonnes CO2e before occupation. Aluminum, glass and steel account for over 90 percent of that total.
Primary aluminum emits 8–16 kg CO2e per kg depending on the smelter electricity source. A 40,000 m2 unitized frame uses ~720 tonnes of aluminum — 8,640 tonnes CO2e at 12 kg per kg.
Recycled aluminum emits 0.5–1.5 kg CO2e per kg. Substituting 75 percent recycled content in the 720-tonne frame reduces framing carbon from 8,640 to 3,240 tonnes — saving 5,400 tonnes, about 1,170 passenger-vehicle-years.
Environmental Product Declarations follow ISO 14025 and EN 15804, covering aluminum extrusions, glass, steel and sealants. They support the LEED v4.1 MR credit and are included in project documentation.
Yes. Life-cycle assessment is run per project using supply-chain EPD data, with recycled content and transport included. Calculations are issued with the project package through the RFI process.
No. Recycled-content aluminum meets the same alloy and structural specifications, and mass reduction comes from value-engineered sections that maintain capacity. Operational and embodied levers are applied together.
The carbon after the factory gate
Transport from Shanghai to a Southeast Asian site adds 80–150 kg CO2e per tonne of aluminum and 30–50 kg CO2e per tonne of glass, depending on whether sea freight or road dominates the leg. On a 720-tonne aluminum frame for a 40,000 m2 project, sea freight at 0.012 kg CO2e per tonne-kilometre adds roughly 58–86 tonnes CO2e for a 6,000 km voyage — small relative to the material itself, but included in Hanart project-level LCA when requested.
Site assembly energy is typically 3–5 percent of total embodied carbon, dominated by crane time, welding and sealant curing. Unitized systems reduce crane hours because panels arrive as complete assemblies, cutting on-site carbon by 20–30 percent relative to stick-built construction on the same facade area. At end-of-life, aluminum is fully recyclable without quality loss, glass is downcycled to aggregate or insulation, and steel is recovered by magnetic separation. Designing for disassembly — mechanically fixed gaskets, bolted rather than welded brackets — raises recovery rates from 60 percent to above 85 percent.
Put real numbers behind your sustainability brief.
Send us your climate data and certification targets — we will respond with glazing, framing and BIPV options mapped to the LEED or BREEAM credits they earn, backed by EPD and test documentation.