PERFORMANCE & COMFORT
Understand the whole window.
Read Uw, Ud, Ug and Uf correctly, and understand why a reference U-value is not a guarantee for your steel window design.
4 minute read
Ask for the complete window or door performance for the actual specification. A glass-only U-value tells only part of the story.
Four values, four different meanings
A U-value describes heat transfer through an element in W/m²K. Lower values indicate less heat transfer under the stated assessment conditions. Always check which element is being described.
| Label | What it describes |
|---|---|
| Uw | Complete window |
| Ud | Complete door |
| Ug | Glazing |
| Uf | Frame |
A thermal break changes the frame construction
The Unico and Unico XS systems in this range incorporate a stainless-steel thermal break. Presto and the listed internal systems are non-thermal constructions. Select the family for the intended location before considering the glass.
A non-thermal internal partition should not be substituted for an insulated external unit simply because the design looks similar. External weather performance, glazing, thresholds and installation details also matter.
Read the conditions beside the headline number
A reference U-value applies to a stated assembly size, glass Ug and frame configuration. Changing the frame-to-glass proportions, glazing, divisions, threshold or opening arrangement can change the result.
Our thermal specifications include those reference conditions so you can compare like for like. We then confirm performance for the size and construction agreed for your project. Compare window Uw with window Uw, rather than with a glass-only Ug.
Performance belongs to the building design
Tell us whether the project is a replacement, extension or new building, and whether there are conservation constraints. In England, the applicable Approved Document L regime can depend on the project and transitional provisions; other UK nations have their own requirements.
Agree the target with the project designer or building control team. Include ventilation, safety, security, access and overheating requirements where relevant. An online configuration is not a building-regulations approval.