A HOUSE-SPOTTER'S GUIDE

Read the windows,
date the house.

Windows are the easiest clock on an old street.

A quiet Georgian brick terrace with rows of tall white six-over-six sash windows and panelled front doors under a pale morning sky — AI-generated image, not a photograph of a real person or place.

Count the panes
Look for horns
Check the glass
Three clues on every old window

Sash windows were the favourite British window for over 200 years, and they changed as glass got bigger and cheaper. Count the panes, look at the bars and the glass, and you can often tell which century a house front belongs to.

Updated 16 October 2026

THE SHORT ANSWER

Bigger glass,
later house.

As glass-making improved, panes grew.
The window front tells the story.

GEORGIAN

Six over six

By the mid-1700s, two rows of three panes in each sash had become the norm, and glazing bars grew slimmer. By about 1800 they were very slender.

Check a window

THE GLASS

Ripples and bubbles

Early 18th-century crown glass was spun into a disc. It can hold tiny bubbles and curved ripples, and only small panes could be cut from it.

About old glass

VICTORIAN

One big pane, with horns

From the mid-1800s larger plate glass arrived. Sashes with one pane each spread, and small 'horns' appeared to strengthen the joints.

See the numbers

A QUICK WINDOW CHECK

What do the
windows look like?

Pick the window type you can see from the street. The bar shows roughly how old that style is: the longer the bar, the older.

Windows are often replaced, so treat this as a clue, not proof. Census records, old maps and local archives can confirm a date.

Window check

Choose a window typeLeaded casements in stone mullionsSashes with small panes and slim barsOne big pane per sash, with hornsSmall panes in the top sash onlyHinged wooden or steel casements

Leaded casements in stone mullionsBefore the sash

Leaded casements, often set in stone mullions, were the standard window before sashes appeared in the late 1600s.

Sashes with small panes and slim barsGeorgian

Six-over-six sashes became the norm by the mid-1700s, and by about 1800 glazing bars were very slender. The earliest sashes had thicker bars and even smaller panes.

One big pane per sash, with hornsVictorian

From the mid-1800s plate glass allowed larger panes. One-over-one sashes spread, and horns were added to strengthen the joints.

Small panes in the top sash onlyEdwardian

Edwardian sashes often brought back multiple panes, sometimes only in the top sash, and used horns as decoration.

Hinged wooden or steel casements20th century

From the early 1900s, mass-produced wooden and steel casement windows made the traditional sash less popular.

Sources: Lancaster City Council, Traditional Sash Windows (Planning Advice Note 14, 2024); Bristol City Council, Traditional windows guidance.

TWO NUMBERS WORTH KNOWING

Old houses
are everywhere.

From the English Housing Survey's
profile of the 2013 housing stock.

35%

Terraced homes built before 1919

The English Housing Survey counted 23.3 million homes in England in 2013. Terraces had the highest share built before 1919, at 35%, while 59% of semi-detached homes were built between 1919 and 1964.

TERRACED HOMES · ENGLAND

54%

London homes built before 1945

London's homes were older than the rest of the country: 54% were built before 1945, compared with 34% of homes outside the capital.

LONDON · ENGLAND

Source: English Housing Survey, Profile of English housing 2013, Chapter 1: Stock profile (Department for Communities and Local Government).

A Victorian red-brick terraced house with a ground-floor bay window of large one-over-one sash windows with small horns at the joints — AI-generated image, not a photograph of a real person or place.

FOUR THINGS TO LOOK FOR

Walk the street,
read the fronts.

You need nothing but your eyes. Look at a row of houses together, because a single replaced window can mislead you.

Count the panes
Many small panes per sash suggest the 1700s; one large pane per sash suggests the mid-1800s or later.
Look at the corners
Small horns sticking down at the sides of the top sash first appeared on Victorian sashes with big panes.
Watch the reflections
Old glass has slight ripples that bend reflections. Modern float glass is perfectly flat.
Check the whole front
Georgian fronts tend to be symmetrical; Victorian houses often add bay windows and patterned brick; Edwardian ones may show porches, tile-hanging or pebbledash.

BLIND WINDOWS AND THE WINDOW TAX

Not every blank
was a tax dodge.

England's window tax began in 1696 and lasted until 1851. Rates were raised in 1784 and tripled in 1797, and some householders blocked up windows to pay less.

But Lancaster City Council's sash window guidance warns not to assume every blind window was a tax dodge. More often a blank opening kept the rhythm of a façade where a real window could not go, such as in front of an internal wall.

Close-up of an old sash window with slender white glazing bars and small panes of slightly rippled glass reflecting a tree — AI-generated image, not a photograph of a real person or place.

Questions

Questions people ask

When did sash windows first appear in England?

Lancaster City Council's guidance says their first use in England is thought to have been at the Palace of Whitehall around 1670, and they stayed the most popular window type for over 200 years.

What are sash horns?

Small projections at the bottom corners of the top sash. They began to appear from the mid-1800s to strengthen the joints of sashes holding larger, heavier panes, and Edwardian sashes often used them for looks.

Can old glass really be told apart from new?

Often, yes. Crown glass from the 18th century can contain tiny bubbles and curved ripples, while most modern glass is made by the float process and is perfectly flat and very reflective.

Are windows a reliable way to date a house?

They are a good clue but not proof, because windows are often replaced. To confirm a date, look for the first census mention of the address, historic Ordnance Survey maps, or local and county archives.

Do I need permission to change old windows?

Lancaster City Council's guidance says listed building consent is needed to replace or alter the appearance of any windows in a listed building, and conservation areas may have extra controls. Ask your local council's planning team.

Read the windows,
date the house.