The 'SMW' section was the back bone of domestic steel windows for decades. This section is effectively the window profile that was used by 'Crittalls' as the basis for their 'homelight' window system.
These sections are still available to us and are generally used when a project requires us to match the existing windows as close as possible irrespective of the thermal rating. Therefore this system is mostly used for refurbishment/listed building projects where the emphasis is on matching the existing window profile and design as close as possible.
SMW windows are mainly used for single glazing and can accommodate standard glass, genuine leaded glass designs and true Georgian glazing bars. It is possible to double glaze these frames with a 'slimlite' double glazed unit to help impove thermal efficiency however this will not meet modern building regulations.