Sash windows are commonly made of two wooden frames where one is above the other and slightly overlapping. This allows either of them to be closed or opened by sliding them up or down within the grooves. These types of windows have had a long European history more so in the United Kingdom but the origin of the first design is very difficult to trace.
Some historians attribute the invention to Dutch technology of the 1600s. A painting known as The Milkmaid by Johannes Vermeer a Dutchman has what is the representation of the framed window adding weight to the theory. The date of the completion of this painting is thought to be somewhere between 1657-61 but some turn down this evidence terming it inconclusive.
Again, the word sash is very similar to the French word chassis which means frame. Therefore, another group of historians believe that the French came up with this technology which was then adopted by the English builders via the Dutch but there is no proof of this also.
Robert Hooke an English inventor is another likely candidate to have come up with the design that shows up in English buildings dating back to the 17th century. However, it is difficult to be certain of this since a book known as Vulgaria by W. Horman, written in the year 1519, is claimed to explain of a window that is opened by moving the frames up and down using a rope.
Even if the historians do not agree, what is common knowledge is that the English developed the technology that made the concept functional and popular. Later on, the designers incorporated a weights and lever system that made the sliding movement smooth and easy to operate even for giant-sized windows. The lever system was aptly concealed in a boxlike case near the window for aesthetic purposes.
Even though by the 17th century building designers such as Inigo Jones were already using the technology, it is during the Georgian 18th century era that the design became common. The royal family utilized the design and its popularity exploded especially during the Victorian reign and the years thereabouts. The buildings that remain from that age have the wooden framed windows whose mechanism works up to today.
The design has stayed on top of the world for almost half a millennium even if it is declining now with the changes in technology. Where it remains, the beautiful design has been innovatively used and changes made to comply with modern requirements. Nevertheless, the basic structure still remains in the UK and the commonwealth as a relic of the English architecture.