It's a "battle" fought daily in architectural offices: On one side, the architect designs an impressive, minimal façade for your new home. They want huge, clean glass surfaces with as little visible aluminium as possible. On the other side, you -the homeowner- want practicality. You want windows that open and tilt for ventilation.
The problem with classic casement windows is their bulk. To open, a window needs the frame (fixed to the wall) and the sash (holding the glass and moving). Viewed from outside, these two profiles add up, creating a thick, bulky aluminium "border" around the glass (typically over 11–13 cm), which "kills" the minimal look.
Fortunately, the aluminium extrusion industry found the solution, called Hidden Sash. Let's see why this technological innovation has become the ultimate obsession of designers and how it can transform your space.
The concept is remarkably clever. In hidden-sash systems, the outer "lip" of the frame is designed to protrude inward. When you close the window, the sash (the moving part) hides completely behind the frame.
When someone looks at your house from outside (from the street or garden), they see only a very thin aluminium frame (around 6–7 cm) and immediately after that, the glass begins. It is absolutely impossible to tell whether the window is operable or a simple fixed pane!
Choosing a hidden sash is not merely a design detail. It offers three enormous advantages that upgrade the property.
By reducing visible aluminium by half, we automatically increase the glazing surface. A hidden-sash window allows up to 20% more natural light into the room compared to a conventional window of the same size. Especially in small openings (e.g. bathroom windows), the difference is dramatic.
Imagine a large living-room opening split in two: the left part is fixed (doesn't open) and the right is an operable door. In conventional systems, the door has a much thicker profile than the fixed pane, creating an ugly asymmetry. With Hidden Sash, the operable and fixed sections look identical from outside, offering a perfectly uniform, "quiet" façade.
To push the minimal result even further, hidden-sash systems are almost always combined with concealed hinges. This means that not only is the sash invisible from outside, but from inside too (when closed) you see no metal hinge protruding. All that's visible is a "clean" aluminium frame and an elegant handle.
Every time we "thin out" a profile, the engineer's concern is whether we lose airtightness and thermal insulation.
The answer from leading extrusion companies (e.g. Alumil, Europa) is emphatic. Modern Hidden Sash systems are heavy-duty and equipped with:
The U-value (thermal transmittance coefficient) of these systems comfortably meets the strictest KENAK requirements.
Operable systems with Hidden Sash are a premium choice and, understandably, their cost is higher than conventional casements. However, if your home's aesthetics are based on clean, modern lines, it is an investment that literally transforms the building's appearance, generously providing light, views and uncompromising security.
💡 Key Takeaway: Hidden Sash systems combine the functionality of a casement window with the minimal aesthetics of a fixed pane. KENAK insulation classes, concealed hinges, 20% more light - all in one indistinguishable, "quiet" façade.
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