Windows are something we rarely think about until one breaks or becomes exceptionally dirty. You may not realize it, but there is more to the glass and frame that make up a typical window than meets the eye. A lot of science goes into designing modern windows that offer spectacular views without sacrificing energy efficiency or structural integrity. Indeed, today’s windows are much different to the windows of the past.


1. Glass Production before Windows

The first historical record of human glass production dates back to about 1500 BC. The document describes a process of heating the necessary materials and forming it into various shapes by twisting, bending, etc. However, it is possible that the earliest stages of glass manufacture go back as far as 3000 BC. Windows were rarely used in the structures of the day, and when they were installed, they were covered with animal skins or left entirely open.

It was not until about 30 BC that glassmakers began making products to cover windows. However, the available technology did not allow for flat and transparent panes that make looking out a window ideal. Typical panes were thick, barely translucent and not uniform. Those who wanted a view from their windows left them open.

2. Glass Meets Windows

By the 14th century, glassmakers had figured out a process of creating windowpanes known as broadsheet. This process created larger, flat panels of glass that were used for windows and leaded lights. By the 17th century, makers were using a new process to create crowned glass, a process that mostly solved the transparency problem and enabled thinner panes to be created. Both methods were limited in terms of the size of panes they created, resulting in large windows made up of multiple panes placed in a framework.

3. Glass Mass Production

German engineers came up with a new way to produce broadsheet glass in the early 1800s that increased the size of the sheets and the overall quality of the product. This process was so efficient that it ushered in an era of mass production that made glass windows commonplace. The process remained continuously in use for nearly 200 years.

4. Early Sash Windows

The earliest sash windows manufactured during the 17th century utilized heavy leaded glass and window frames consisting of several layers of smaller panes. Although these windows were effective, they were rather heavy and awkward to open. Engineers made the task easier by attaching counterbalance weights on either side of the sash.

5. Windows as a Sign of Wealth

The Victorian era ushered in a period in which the windows in one’s house were an indicator of wealth. Those of greater means chose windows consisting of only one or two panes of glass while lower-class homes still had windows composed of six or nine panes. The smaller panes were cheaper because they were easier to manufacture and ship.

6. Casement Windows

During the early 1900s, window makers began looking for ways to solve the draftiness of sash windows, especially in colder climates. They began developing casement windows made of wood or steel, discovering along the way that such windows could be mass-produced at a much lower cost than their sash counterparts could. By the end of World War II, casement windows ensured the doom of the traditional sash.

7. Energy Efficiency and Building Codes

Today, traditional sash windows are all but extinct except for specific cases of history preservation. The need for greater energy efficiency combined with strict building codes makes sash windows both impractical and much too expensive to use. Though history lovers lament the transition to casement windows, it is what it is. The job of the modern preservationist is to replicate the look of the old sash window while still maintaining efficiency and code compliance.

Now you know a little bit more about window making. Next time you are looking out one of your windows at home or the office, keep in mind there was a day when that would not have been possible. Thanks to some very smart people with some excellent ideas, today’s windows make life a lot better.

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