Georgian bars divide a pane into a grid of small rectangles. Astragal bars are applied bars that sit on the glass surface and create a genuine shadow line, so they look far closer to true divided panes. Leaded designs use lead strip laid over or within the glass in patterns. For a convincing period look on a modern window, astragal bars are almost always the right answer.
- Georgian bars usually means an internal bar sealed inside the unit, the least convincing option
- Astragal bars sit on the glass face and cast a shadow, which makes them read as real
- Bar width and grid proportion matter more than bar type. Too many small panes looks wrong on a wide window
- Leaded designs suit older properties and door glazing, not large window openings
- Frame sightlines matter as much as the bars
Period detailing on replacement windows goes wrong more often than any other specification choice, usually in the same way: the right idea at the wrong scale. A house that had six over six sash windows gets a modern casement with a grid of tiny squares sealed inside the glazing, and the result reads as pastiche rather than restoration. The components to do it properly all exist.
What is the difference between the bar types?
Three quite different things get called Georgian bars in conversation, and they produce three quite different results. Knowing which you are being offered is the most useful thing here.
| Type | How it is made | How it reads |
|---|---|---|
| Internal bar | Sealed inside the cavity between the panes | Flat, no shadow, visibly behind the glass. Least convincing, easiest to clean |
| Astragal bar | Bonded to the outer and inner glass faces, with a matching internal spacer | Casts a genuine shadow line, so the eye reads separate panes |
| Through bar | A structural bar dividing the opening into separate glazed units | Genuinely separate panes. Most authentic, most expensive, reduces glazed area |
| Leaded | Lead strip applied to the face or set within the unit | Decorative rather than architectural period glazing |
How do you get the grid proportion right?
Look at what the house originally had, or at neighbours that kept their original windows. Georgian and early Victorian patterns were driven by the largest practical sheet of glass at the time, which is why panes tend to be a comfortable rectangle, taller than wide. Six over six and eight over eight are common on a sash. On a wide casement the same pane proportion means fewer, larger panes, not more small ones.
The frequent mistake is scaling up the number of bars rather than the pane size. A wide window given a dense grid of small squares looks like a leaded light rather than a Georgian window. Better to divide a wide opening into a few tall rectangles echoing the original proportion. Our heritage windows and uPVC sash horn windows ranges are built around those proportions rather than a generic grid.
Where do leaded designs belong?
Leaded work is a different tradition suiting different places: door glazing, fanlights and toplights, stair windows, and later Victorian and Edwardian properties where decorative glazing was original. It sits happily on a timber door or the toplight above one. What it does not do is make a large modern opening look Georgian, because the two traditions are a century apart.
The choice is between lead applied to the surface of a sealed unit and genuine leaded glass encapsulated within one. Surface applied lead is common and serviceable, though it needs care not to lift the strip when cleaning. Encapsulated leadwork sits inside the cavity, which is more durable, better for exposed positions and the right approach when reproducing an original design.
Do bars affect the window’s performance?
Slightly, and the effect differs by type. Internal bars interrupt the sealed cavity, which has a small effect on thermal performance and on a wide bar can marginally affect the U-value. Astragal bars sit outside the cavity on both faces, so they have almost no thermal effect. Through bars reduce the glazed area and increase the framed area, which changes the whole window figure more noticeably. Internal bars are easiest to clean around, while astragal bars need a little more care but are bonded rather than clipped, so they do not work loose. Our guide to double glazed window performance explains which figures the bars influence.
What about conservation areas and listed buildings?
This is where the detail stops being a matter of taste. In a conservation area the local authority can be specific about bar type, bar width, sightlines and pane proportion, and an internal bar is frequently refused where an astragal or through bar would be accepted. Listed building consent goes further and can specify materials as well as pattern. Historic England publishes detailed guidance on traditional windows in its technical advice library.
Establish the local authority’s expectations before you order, not after. The Planning Portal covers when consent is needed, and we set out how the process works in our article on window replacement in conservation areas. Where a property is listed, the sequence is a pre-application conversation, then a specification, then an order.
What drives the cost?
Internal bars are least expensive, being a component added inside the unit during manufacture. Astragal bars cost more, tracking the number of bars and total bonded length, since it is a labour operation on both glass faces plus a matching internal spacer. A dense grid therefore costs considerably more than a division into a few panes, which happens to align with the better looking answer.
Through bars sit above both, since the opening becomes multiple glazed units in a structurally divided frame. Leaded work is priced by design complexity and piece count, with encapsulated above surface applied. Across all of them, spend on a few well proportioned, properly detailed divisions rather than many cheap ones. Our windows pages set out what each range supports.
Frequently asked questions
Are Georgian bars and astragal bars the same thing?
Can I add glazing bars to my existing windows?
Do glazing bars make windows harder to clean?
How wide should a glazing bar be?
Will a conservation officer accept internal glazing bars?
Can leaded glass be double glazed?
Get a sample against the house
Period detailing is a judgement made by eye and hard to make from a brochure. Hold a sample bar and pane against the actual elevation in daylight and the right answer usually becomes obvious. Our team can bring the options out and, in a conservation area, help you reach a specification the local authority will accept.