The most glass, the least frame, the best rating.
A fixed window has no sash. That's why it's the most efficient window you can buy: no moving parts, no sash frame, nothing to adjust. In a view home it's the frame for the view. In a stairwell or a gable it's the light. And it's usually paired with an opening sash nearby, so the room still breathes.
Why a fixed window rates better
U-factor is an average over glass and frame. Glass in the center of a triple-pane unit insulates better than any frame. A fixed window has less frame per square foot, so its whole-window U-factor is lower than an operable window of the same size and glass. On MB-79N, for example, product data shows fixed windows starting lower than tilt-and-turn.
Combinations
- Picture window with tilt-and-turn sashes either side.
- Fixed lower pane with a tilt-only transom above.
- Floor-to-ceiling fixed glass with a hidden-sash operable unit that looks identical (MB-Slimline, MB-79N Pro, Synergic).
- Glass corners without a corner post (MasterLine, SlimLine).
Fix the big pane, open the small one. You get the view and the air.
Large glass, real limits
Big units are heavy: triple glass weighs roughly three times single glass of the same thickness per pane. Size limits depend on the system, glass build-up, wind exposure and how we get it into the house. Safety glass is required near doors, floors and tubs under the building code; we specify it where needed.
Every frame material comes in fixed windows. For the largest panes: MB-86N, MasterLine 8 Elite, MB-104 Pro. For value: P-300.