Wooden windows and exterior doors - Designing the frame-sash connection

While making a single-piece watertight wall may seem straightforward, creating a structure that opens and closes while remaining watertight is undeniably more complex.

Indeed, for centuries, windows and exterior doors were not watertight, and entry was only crudely controlled; the best achievements were far from the level of watertightness that seems obvious today.

The first approaches to achieving a better seal were based on common sense and on experience with watertight objects or equipment: interposing a seal between the medium to be protected and the hostile environment, the reaction of which by itself ensures watertightness - this is the submarine or jar technique.

Its transposition to windows was a failure due to :

• discontinuity of the sealing barrier due to the complexity of the profiles ;

• the necessary reaction of the seal to ensure tightness, which is incompatible with an acceptable operating force;

• the rigidity of the moving parts (leaves) is well below what is required to take up the reaction of the seal.

It wasn't until the early 1970s that the industry developed, empirically (through testing), the principles of watertightness for a sash-frame connection, and it wasn't until the early 1980s that the limits of each parameter were more precisely quantified.

Given the number of dimensional combinations for wood profiles, and the role of wood finishes and their additives, this avenue is not yet exhausted.

To achieve a given level of performance, the design of the frame-sash connection must follow certain precise rules that are more or less specific to each function.