---
title: "Glass - GWP and renovation use"
canonical_url: https://fremtidenstegnestue.dk/en/knowledge/materials/glas
markdown_url: https://fremtidenstegnestue.dk/en/knowledge/materials/glas.md
author: "Fremtidens Tegnestue"
page_type: material
primary_intent: "Explain use, GWP and renovation relevance for Glass."
primary_keyword: Glass
audience: "Homeowners, studios and agents researching material choices."
summary: "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."
source_basis:
  - "ECO Platform EPD average"
  - "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/vinduer
    relation: alternative-material
  -
    url: https://fremtidenstegnestue.dk/en/knowledge/materials
    relation: hub
  -
    url: https://fremtidenstegnestue.dk/en/knowledge/concepts/lca
    relation: concept
status: published
---
# Glass - GWP and renovation use
Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/materials/glas
Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/materials/glas.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
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.
## 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 | 0.86 kg CO₂-eq/kg |
| Density | 2500 kg/m³ |
| Expected lifetime | 30–50 years (insulating glass units), the glass itself can last 100+ years |
## Use

- Windows and thermal panes
- Facade glazing and glass partitions
- Rooflights and dome rooflights
- Bathroom glass and partitions
## Renovation relevance
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.
## Comparison

| Material | GWP |
| --- | --- |
| Glass (float glass) | 0.86 |
| Aluminium (primary) | 8.24 |
| Structural timber | -0.72 |
| Concrete | 0.13 |
## FAQ
### 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.
## Sources and basis
- ECO Platform EPD average
- [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
- [Windows (timber/aluminium)](https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer): 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/glas) 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.