Energy efficiency
How to assess aluminium windows and doors against energy-efficiency requirements: whole-unit U-values, thermal breaks and glazing are checked for the selected project.
Compare the whole unit, not only the centre-pane figure, and check the final route against the drawing before relying on a number.
Whole-unit U-valuesFrame and glass are assessed together, not the centre-pane alone.
Thermally broken aluminiumLow-conductivity break between inner and outer profiles.
Approved Document LCheck the current guidance and project requirements before relying on a value.
Energy performance should be considered for the whole unit: frame, glass, edge detail and configuration together, not the centre-pane figure on its own. Confirm the relevant value for the selected product route, size and opening style before relying on it.
Aluminium uses a thermal break, a low-conductivity barrier between the inner and outer profiles, to cut heat loss through the frame. The break depth, the profile and the glazing combine to set the result.
Double or triple glazing, low-E coatings, warm-edge spacers and gas fill all move the U-value. The glass is specified with the frame so the target is realistic for the size, weight and exposure.
For dwellings in England, the current Approved Documents provide statutory guidance on meeting the Building Regulations, including Approved Document L for conservation of fuel and power. The relevant requirements and any transitional provisions must be checked for the project rather than inferred from a marketing figure.
Low-U routes are project assessed. Send sizes, opening style, glass target and drawings, then request the current calculation or supporting evidence for the selected product route before an order is placed. Bigger glass, slim sightlines and exposure all affect what is realistic, so the specification is set against the project rather than a brochure figure.
Most relevant on windows and tilt-and-turn routes: aluminium casement windows, aluminium tilt and turn windows, and the trade note on low-U routes for trade estimates.
Related guides
For the detail behind the numbers, see the guide to aluminium U-values and how an aluminium thermal break works. For the wider spec, see weather ratings, acoustic performance and maximum sizes. To weigh the frame material itself, read aluminium vs uPVC windows and doors or aluminium vs timber. On glass, finish and style, see glazing explained, finishes and colours and window styles.
The whole-unit figure considers the window or door assembly, not only the centre of the glass. The relevant value depends on the selected product, size, glazing and configuration, so it must be checked against the actual project.
State the project type and target, then request the current calculation or supporting evidence for the selected product route. A web-page figure or centre-pane value is not a design calculation or compliance confirmation.
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