---
title: "Windows (timber/aluminium) - GWP and renovation use"
canonical_url: https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer
markdown_url: https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer.md
author: "Fremtidens Tegnestue"
page_type: material
primary_intent: "Explain use, GWP and renovation relevance for Windows (timber/aluminium)."
primary_keyword: "Windows (timber/aluminium)"
audience: "Homeowners, studios and agents researching material choices."
summary: "A window is a combined unit of frame and glass. Carbon footprint varies significantly by frame material: timber windows have low footprint, aluminium windows are high, and composite (timber/alu) is in between. Energy efficiency (U-value) is the most important parameter for climate impact over lifespan."
source_basis:
  - "estimatee based on the EN 15804 average (average timber/aluminium composite)"
  - "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/glas
    relation: alternative-material
  -
    url: https://fremtidenstegnestue.dk/en/knowledge/materials/trae
    relation: alternative-material
  -
    url: https://fremtidenstegnestue.dk/en/knowledge/materials
    relation: hub
  -
    url: https://fremtidenstegnestue.dk/en/knowledge/concepts/lca
    relation: concept
status: published
---
# Windows (timber/aluminium) - GWP and renovation use
Canonical URL: https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer
Markdown URL: https://fremtidenstegnestue.dk/en/knowledge/materials/vinduer.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
A window is a combined unit of frame and glass. Carbon footprint varies significantly by frame material: timber windows have low footprint, aluminium windows are high, and composite (timber/alu) is in between. Energy efficiency (U-value) is the most important parameter for climate impact over lifespan.
## 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 | 35 kg CO₂-eq/m² |
| Density | varierer |
| Expected lifetime | 30–60 years |
## Use

- Residential windows
- Facade windows and elements
- Roof windows
- Patio doors and sliding windows
## Renovation relevance
Window renovation is typically the energy renovation measure with the shortest payback period, especially going from single to double or triple glazing. Always specify the U-value and be aware of cold bridges in the frame.
## Comparison

| Material | GWP |
| --- | --- |
| Timber window | 20 |
| Timber/aluminium composite | 40 |
| Aluminium window (recycled) | 50 |
| Aluminium window (primary) | 100 |
## FAQ
### What is the CO₂ difference between timber and aluminium windows?
Timber windows have GWP of approximately 15–25 kg CO₂/m². Aluminium windows (primary alu) 80–120 kg CO₂/m². Timber/alu composite 35–50 kg CO₂/m². Timber is clearly best climatically.
### Which windows require least maintenance?
Aluminium windows are almost maintenance-free (no painting needed). Timber/alu composite requires only interior maintenance. Timber alone requires painting/oiling externally every 3–7 years.
### When should windows be replaced?
Windows should be replaced when: U-value is above 2.5 (single glazing), there is condensation in thermal panes, the frame is rotted, or draughts cause discomfort. Energy renovation typically includes window replacement.
### Is it better to replace only the pane or the whole window?
If the frame is in good condition and original glass thickness/frame size permits, the pane can be replaced alone. This is cheaper and reduces waste. A carpenter or window manufacturer can assess whether this is possible.
## Sources and basis
- estimatee based on the EN 15804 average (average timber/aluminium composite)
- [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
- [Glass](https://fremtidenstegnestue.dk/en/knowledge/materials/glas): alternative-material
- [Structural Timber](https://fremtidenstegnestue.dk/en/knowledge/materials/trae): 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/vinduer) 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.