What is the glazing bar layout of historic windows?
The glazing bar layout is the division of a window into smaller panes by timber glazing bars or lead cames. In historic Dutch windows it is closely tied to glassmaking technology: as long as only small panes could be made, a window consisted of many lights. As glass became larger and better, glazing bars disappeared step by step.
Development in outline
The overview below follows the development in Amsterdam. Dates are indicative; practice varied by region and by client.
| Period (approx.) | Type | Feature |
|---|---|---|
| Early 17th century | Cross window | A timber mullion and transom divide the frame into four; small panes of about 10 × 15 cm in leaded lights |
| Early 17th century | Half cross window | Variant with a transom only, also leaded |
| Around 1650 | Cross window with timber glazing bars | Larger panes of about 20 × 25 cm; timber bars replace the lead |
| 17th century | Cloister window | Half cross window with timber glazing bars |
| From about 1685 | Sash window | Fixed upper light and vertically sliding lower sash, both with glazing bars |
| Around 1700 / 1750 / 1790-1850 | Five, four and three panes high | Fewer, larger panes per sash height |
| Around 1810 | Empire window | Inward-opening casements with a heavier central stile |
| About 1860-1930 | T-window | One pane above, two below; industrially made glass |
| About 1930-1950 | H-window | A single pane in both upper and lower sashes |
What to watch for with old windows
- Windows don’t reliably date a house. Windows were often modernised; a 17th-century house may have 19th-century sashes. If in doubt, ask a building historian.
- True or stick-on bars? With true glazing bars each pane sits in its own rebate. Bars stuck onto one large pane look different close up, especially in shadow and profile.
- Insulating while keeping the bars. Slim double glazing designed for historic buildings sometimes fits existing rebates. Secondary glazing on the inside is an alternative that leaves the exterior untouched.
- Sizes and profile. Bar thickness and moulding largely determine how old a window looks. Copy the original profile when making replacements.
- Listed building? Altering or replacing windows then needs consent. Agree the approach with the local authority first.
Related terms
- Cross window
- Cloister window
- Empire window
- Cross glazing bar
- Three-light window
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.