W20 vs W50 Steel Windows: Which Section?
W20 and W50 are the two steel sections most projects choose between. They look similar but solve different problems. Here is how to decide.
W20: the heritage section
W20 is the traditional hot-rolled section with the slimmest sightline (around 20mm) and the most authentic crittall-style look. It is the default for conservation areas, listed buildings and period restoration.
It is not thermally broken, so for heritage work it is usually paired with appropriate glazing and accepted as part of the like-for-like character.
W50: the thermally broken section
W50 adds a polyamide thermal break to cut heat transfer and condensation, while replicating the slim W20 appearance on a slightly wider section (around 50mm). It takes double or triple glazing comfortably.
It is the right choice for new builds, extensions and any project where energy efficiency and comfort are priorities.
Which should you choose?
Choose W20 when authenticity and the slimmest possible sightline matter most — typically heritage and conservation work. Choose W50 when thermal performance and running costs matter most — typically contemporary and new-build projects.
If you are unsure, tell us about the property and how it is used and we will recommend the section that fits.
Frequently asked
- Is W50 just a thicker W20?
- In effect, yes — W50 keeps the W20 aesthetic on a slightly wider section that houses a thermal break for far better energy performance.
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Tell us your sizes and target dates and our team will prepare a considered estimate. We survey, make and install across mainland UK.