AWS 75.SI is arguably the most flexible window in the Schüco range. Well insulated enough for new build, but proportioned in a way that suits replacement work on brick-built 1970s and 1980s houses without an awkward oversized frame.
The thermal break in plain terms
The SI suffix marks an enlarged thermal break, which pulls the Uw figure down to 0.87 W/m²K. In practice, that is a strong result for a straightforward 75 mm frame.
Configurations available
The system carries the usual family of casement, tilt-and-turn, fixed, top-hung and corner-window options — the corner detail without a mullion is particularly useful on contemporary rear extensions.
What actually affects the numbers
The realised U-value of the finished window depends heavily on the glazing unit specified. It is worth asking a supplier for a Uw figure for the actual configuration, not the profile alone.
Readers looking for a Stevenage-based supplier will find 5EC's aluminium windows a practical first port of call — the firm holds authorised-supplier status for the brands covered here.
Detailed technical documentation is available on the manufacturer's data.