Double hung window and storm window operation.
The Double Hung Window
The sash window, better known as the double hung window in America, is an old invention speculated to originate in the seventeenth century from England, the Netherlands, or France. The word “sash” is french but there are three hypotheses suggesting origin from each. The double hung window and casement window are the most popular styles in the United States.
The historic single pane wooden double hung window, in my opinion, is best designed most common window to date. The double hung window is “double hung” because two sash are hanging on cotton rope and are designed to move into opened or closed positions. Both sash can be opened to allow hot air collecting towards the top of the ceiling to be vented. The window assemblies are typically 60 inches tall with the upper most portion of the window placed above your average 6′ tall human. This is intentional so the inhabitant can control the air in the dwelling to their liking through window operation. When hot air escapes through the top sash, cool air from the outside is drawn in like a siphon through the lower sash. This function of air movement will also aid in removing excess moisture build up on the interior side of the glass which helps preserve the integrity of the window.
Both the double hung window and casement window are crafted using a high quality putty and are designed to be repaired. Glass is set into and finished using putty glazing. The putty is how the glass adheres to the sash wood and gives the sash assembly its over all rigidity. The putty can be softened and removed using dry heat or steam and the glass can be reset and glazed back into a cleaned up sash for additional years of service.
Historic style single pane windows are joined with mortise (female) and tenon (male) joinery that can be pinned together with wood dowels or stainless steel staples. Historic windows were typically pinned with clipped steel nails that can be removed to allow the two joint pieces to slide apart allowing for rail (sides) or stile (top or bottom) repair.
A historic style double hung window has a hidden wall cavity that houses a weight equal to half the weight of the sash. There are two weight pockets on either side of the sash hidden underneath the casing (or trim). There are two weights per weight pocket. One for the upper sash and one for the lower sash. The cast iron weights hidden in the walls are called counter-balances. This system allows for an unlimited range of double hung window sizes because you can scale the size of weights, ropes, and pulleys to match the size of the sash. The weights are attached with a high quality cotton rope and run on a pulley which reduces operating friction. Friction can be further reduced using pulleys with ball bearings (a later advancement being implemented today.).
Louw, H. J. “The Origin of the Sash-Window.” Architectural History, vol. 26, 1983, pp. 49–150. JSTOR, www.jstor.org/stable/1568434.