• The sliding window had existed in Europe as early as the thirteenth century. During this period these windows were no more than vertical sliding timber shutters.
• By the end of the sixteenth century they had become glazed, horizontally sliding timber windows, and by the mid seventeenth century were superseded with vertical sliding windows, introduced mainly in France. This type of window was used in passageways and staircases, as casement windows (which opened inwards) could be an obstruction to the occupants.
• Sliding windows were used in many English manor houses, though there is little historical evidence of their existence before the seventeenth century.
• It is during the post restoration period, with the nobility returning from France, that much of the sophisticated architecture of the vertical sliding window crossed the Channel to England. It is believed that one of the first fully glazed vertical sliding windows was installed for Henrietta Maria, the Queen Mother, who, returning from France with her entourage, which included French joiners, influenced the refurbishment of Somerset House in London, which years later Ventrolla would renovate.
• The exact timing of the development of the vertical sliding sash window (with a counter balance) is not precise, and numerous theories are proffered. It is widely believed that it was actually invented in England. A progression from the original vertical sliding window, it was glazed with small squares of glass approximately 250mm x 250mm, and thick glazing bars in excess of 40mm made it an extremely heavy window to open.
• The art of counter balancing was first used in doors. There is documented evidence in the “Office of Works Account 1663” of weights and lines being fitted to doors in various buildings at Whitehall. It was then only a matter of time before this development was used in windows. The Office of Works has further accounts which state that the Master Joiner, Thomas Kinward, installed lines and pulleys into the windows at the Queen’s private apartment in Whitehall at the end of 1669, though there is no mention of the counter weights.
• In 1672 Ham House, the London property of the Duke and Duchess of Lauderdale, underwent alterations. There is clear evidence that the windows installed were counter balanced sash windows, again by Thomas Kinward, who, together with Christopher Wren, signed the accounts.
• It was never patented, nor did anyone claim to be its inventor.
• The earliest sash windows had solid oak frames, with a groove cut out for the weights. Only the bottom sash opened, the top sash being fixed in position. Little time passed before the development of the boxed frame, which was made in sections to allow the now hidden weights to pass each other. From the end of the seventeenth century the mechanics of the sliding sash window changed very little.
• The number of panes slowly reduced, as did the thickness of the glazing bars, but it was not until the removal of the duty on glass in 1845, when the price of the plate glass fell by three quarters, that the individual panes became larger, with only two panes per sash. Indeed, a sign of wealth was to have one pane per sash! It was in the mid nineteenth century that horns on the top of the bottom sash and the bottom of the top sash first appeared, to give extra support to the glass.
