Glass.
Glass has a moderate CO₂ footprint. The energy savings from good insulation performance far outweigh production CO₂. Choose low-energy glass with U-value below 1.0. Read the numbers together with function, lifespan, detailing and the specific building element.
- Carbon Footprint (GWP)
- 0.86 kg CO₂-eq/kg
- Source: ECO Platform EPD average
- Density
- 2500 kg/m³
- Expected Lifespan
- 30–50 years (insulating glass units), the glass itself can last 100+ years
How to use this assessment
The assessment of glass is a first decision basis. Carbon numbers, density and lifespan give a point of comparison, but the material must always be read together with structure, moisture, fire requirements, detailing, maintenance and the condition of the existing building. A good material choice is therefore both a data question and an architectural judgement. The useful next step is to clarify which questions should be examined further before the material is specified in a project.
What is glass?
Glass in buildings is overwhelmingly float glass — made by melting sand, soda ash, and lime and floating it on a bath of molten tin. Used for windows, facade glazing, rooflights, and glass partitions. Modern energy panes with low-emission glass and argon fill give U-values below 1.0 W/m²K.
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 Windows and thermal panes
- check_circle Facade glazing and glass partitions
- check_circle Rooflights and dome rooflights
- check_circle Bathroom glass and partitions
In Renovation
Window renovation is one of the most important energy renovation measures. Replacing single glazing with modern energy panes can halve heat loss through windows. Consider whether the frame can be preserved and only panes replaced.
Questions about glass
What is a good U-value for windows?
U-value indicates heat loss per m² window. BR18 requires U ≤ 1.2 W/m²K for new windows. Triple glazing achieves U = 0.5–0.8. Lower U = better insulation. For energy renovation, aim for U ≤ 1.0.
When should thermal panes be replaced?
Thermal panes typically last 20–30 years. Signs of spent panes: condensation between glass layers (seal failure), scratches, cracks, and noticeable cold at the window edge. The frame itself may still be good.
Is triple glazing always best?
Not necessarily. Triple glazing is heavier, more expensive, and slightly reduces light transmission. In south-facing windows, good double glazing can give better heat balance (solar gain) than triple. Expert advice is needed.
Can glass be recycled?
Float glass can technically be recycled, but in practice it is rarely remelted into new float glass. It is used for glass cullet, glass wool insulation, and road aggregate. Recycling rate for building glass is low in Denmark.
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