Technical information notice. Technical information on this page is general product-selection guidance, not a certification, compliance statement, design calculation or order confirmation. Before relying on a figure or standard, request current evidence for the selected product route, size, glazing, hardware and project. See our technical information.
Guide
Aluminium U-Values Explained
A U-value measures how much heat passes through a unit: the lower the number, the better the insulation. For aluminium glazing the figure you specify and the figure you build to are not always the same, so this guide sets out what U-values mean, the numbers to expect by system, and how the whole-unit value is confirmed at quote.
Trade onlyWe fabricate and supply the trade. Homeowners are routed to vetted installers.
Fabricated in Haydock, St HelensTrade-first aluminium fabricator, based in the North West.
Quote-confirmed specsWhole-unit Uw is confirmed for your sizes and glazing at quote.
What is a U-value?
A U-value is the rate of heat transfer through a building element, measured in W/m2K. The lower the number, the less heat escapes and the better the thermal performance.
For glazing you will see three notations. Ug is the glass alone. Uf is the frame. Uw is the whole window or door, combining glass, frame, spacer and the way they meet. Uw is the figure that matters for Building Regulations and for real performance, because a strong glass unit in a weak frame still loses heat at the edges.
Aluminium conducts heat, so thermal performance comes from the polyamide thermal break that separates the inside and outside of the frame. The depth of that break, the glazing unit and the spacer bar together set the Uw you achieve.
Request current product evidence for the selected route, size, glazing, hardware and project before relying on the specification.
Ug, Uf or Uw: which figure should you specify?
Specify to Uw. A glass supplier quoting a low Ug is describing the centre-pane glass, not the finished unit, so two products with the same Ug can perform very differently once framed.
Quote Uw against the actual sizes. Larger sashes carry proportionally more glass to frame, which usually improves the whole-unit figure; smaller units sit closer to the frame value. That is why a single headline number rarely fits every opening on a project.
Confirm the whole-unit Uw at quote for your sizes, glazing and configuration. Tell us what you need and we quote the right system.
Aluminium U-values by system
A U-value below is printed only where the U-value table for the system we make gives one at a named glass, and for doors in the worst tabulated configuration. Everything else is at quote. The value for your opening varies with size and glazing, and is confirmed at quote.
Casement windows: Uw 1.4 W/m²K double-glazed (Ug 1.0), 1.2 triple-glazed (Ug 0.7), at the 1357.5 x 1480 mm test size. Confirmed at quote for your opening. Tilt-turn windows: Uw 1.4 W/m²K double-glazed (Ug 1.0), 1.2 triple-glazed (Ug 0.7), at the 1537.5 x 1480 mm test size. Confirmed at quote for your opening.
Bifold doors: Uw 1.45 W/m²K with Ug 1.0 glass, 1.2 with Ug 0.7 glass, in the worst tabulated configuration. Confirmed at quote for your opening. Leaves up to 1.2 x 3.0m, a traffic leaf to 130kg on four hinges, up to 14 leaves, and around 90% clear opening. Sliding doors have their Uw confirmed at quote, with sashes up to 2.5 x 3.0m and 300kg on lift-and-slide, a 35mm interlock, and around 50 to 65% clear opening depending on configuration.
Entrance doors: Ud 1.3 W/m²K with Ug 1.0 glass, 1.1 with Ug 0.6 glass, in the worst of the four tabulated door types. Confirmed at quote for your opening. Commercial doors: U-value at quote for your size and glass. Heritage door U-values are confirmed at quote. For facades, curtain walling carries panels up to 1500mm wide and 250kg on a 62mm frame system, with the Ucw confirmed at quote for your glazing and typology.
| Casement | Uw 1.4 W/m²K double-glazed (Ug 1.0), 1.2 triple-glazed (Ug 0.7), confirmed at quote for your opening |
|---|---|
| Tilt-turn | Uw 1.4 W/m²K double-glazed (Ug 1.0), 1.2 triple-glazed (Ug 0.7), confirmed at quote for your opening |
| Bifold | Uw 1.45 W/m²K with Ug 1.0 glass, 1.2 with Ug 0.7 glass, confirmed at quote for your opening; leaves to 1.2 x 3.0m; traffic leaf to 130kg on four hinges; up to 14 leaves; ~90% clear opening |
| Sliding | U-value at quote; sashes to 2.5 x 3.0m / 300kg on lift-and-slide; 35mm interlock; ~50-65% clear opening |
| Entrance | Ud 1.3 W/m²K with Ug 1.0 glass, 1.1 with Ug 0.6 glass, confirmed at quote for your opening |
| Heritage | U-value at quote |
| Curtain walling | Ucw at quote; panels to 1500mm wide / 250kg; 62mm frame system |
| Commercial | U-value confirmed at quote for your size and glass |
How U-values relate to weather and acoustic performance
Thermal performance sits alongside weathertightness and acoustics, and the same systems carry independent ratings for those. We supply to weather and air to Class 4, watertightness to Class 9A, and wind resistance to Class C5 where the system and install are specified for it.
Acoustic reduction reaches up to Rw 46 dB where specified, which is the route for roadside, trackside and city-centre projects. Security follows the same logic, with PAS 24 routes available where specified. See security and energy efficiency for how these are specified together.
These ratings are independent of the U-value, so a low Uw does not automatically mean a high weather or acoustic class. State the demands of the opening and we match the system to all of them.
How to specify and quote
Give us the opening sizes, the configuration and the target Uw, plus any weather, acoustic or security class the project calls for. We confirm the whole-unit Uw and the matching ratings against your drawings.
We fabricate and supply the trade: installers, builders, architects, joiners and commercial clients. Homeowners are routed to a vetted installer via find an installer.
Browse the range at products, see how we work with the trade at trade, or send your requirement to quote and we will quote the right system.
Common questions
What is a good U-value for aluminium windows?
Specify to whole-unit Uw rather than glass alone. Our casement system's table gives Uw 1.4 W/m²K double-glazed (Ug 1.0), 1.2 triple-glazed (Ug 0.7) at its test size, and the tilt-turn system's the same at its own, each confirmed at quote for your opening. The figure for your window depends on the system, the sizes and the glazing.
What is the difference between Ug, Uf and Uw?
Ug is the centre-pane glass value, Uf is the frame value, and Uw is the whole window or door combining glass, frame and spacer. Uw is the figure that counts for Building Regulations and real performance, because it accounts for heat loss at the frame and edges, not just the middle of the glass.
What U-values do VitrineAlu aluminium doors achieve?
Bifold doors: Uw 1.45 W/m²K with Ug 1.0 glass, 1.2 with Ug 0.7 glass, confirmed at quote for your opening. Entrance doors: Ud 1.3 W/m²K with Ug 1.0 glass, 1.1 with Ug 0.6 glass, confirmed at quote for your opening. Sliding and heritage door U-values are confirmed at quote for your sizes, glazing and configuration.
Does a low U-value mean good weather and acoustic performance too?
No. The U-value measures heat loss only. Weathertightness, air, wind and acoustic performance are rated separately. Our systems supply to weather and air permeability Class 4, watertightness Class 9A, wind Class C5 and acoustic reduction up to Rw 46 dB where specified, independent of the Uw.
Can I get a single U-value for a whole project?
Not usually. Larger units carry more glass to frame and tend to give a better whole-unit figure than small ones, so the Uw varies opening to opening. Send your sizes and configurations and we confirm the Uw for each at quote.
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Verified business details
VITRINEALU LTD
- Companies House
- Company number 12927857
- Fabrication works
- Unit 1 Nassau Business Park, Bahama Road, Haydock, St Helens, WA11 9FW
- Membership
- Council for Aluminium in Building member
- Phone
- 0330 133 3622