What is a Viennese glazing bar (Wiener Sprosse)?
A Viennese glazing bar, from the German “Wiener Sprosse”, is a glazing bar bonded to the inside and outside of a single, continuous double-glazed unit, with a spacer bar in the cavity exactly in between. In English it is often called a stuck-on or simulated divided lite bar with a shadow bar. From outside and inside the window looks as if it is made up of separate small panes, while it is actually one insulating unit.
Three ways to make glazing bars
- True dividing bars: real bars with a separate pane in each opening. The most authentic, but with many edges, so more heat loss and more risk of leaks.
- Bars in the cavity: a profile only between the panes. The glass stays flat on both sides, which looks less convincing.
- Viennese glazing bar: bonded bars on both faces plus a spacer in the cavity. Close up and at an angle it looks very much like a true bar.
Advantages
- Insulation: one continuous unit insulates better than many small units with their own edge seals.
- Appearance: the historic look of a window with glazing bars is kept.
- Maintenance: fewer sealant joints and glazing beads that can leak or rot.
Points to watch
- Alignment: the bonded bars and spacer must line up exactly, otherwise you see a double line when looking at an angle. Choose factory-applied bars.
- Bond: outside, the bars face sun and rain. Ask about the adhesive and the warranty on the bond.
- Width and profile: copy the dimensions and moulding of the original bars to keep the existing facade appearance.
- Listed buildings: the local authority may set requirements for the type of glazing bar. Check first.
- Cleaning: windows with bonded bars take longer to clean.
Related terms
- Glazing bar
- Cross glazing bar
- Glazing bar layout of historic windows
- Secondary glazed windows
- Window sash
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