Secondary Glazing Secondary glazing is the installation of new, independent secondary window frames on the interior side of the existing window. The key benefits of secondary windows are very similar to double glazing. With improved insulation and draught proofing, your room will stay warmer for longer than single glazing, helping save money on heating and fuel bills. Secondary glazing is ideally suited to listed, period, historical and heritage buildings. Secondary glazing will also significantly reduce traffic and outside noise and also improve window security from intruders. They are very suitable for houses, bungalows, apartments, offices, studios and listed period, historical and heritage buildings. Secondary glazing is available in any size and can be glazed with a choice of glass types including patterned, obscured, toughened and heat reflective.