VISIBLE DIVISION
As shown through this sequence of window grille
options from Marvin, deciding between simulated (SDL) or true (TDL) divided lights in insulated replacement windows often comes down to affordability versus architectural appearance.
The least expensive double-glazed option is to place the muntin grille between the sheets of glass. While this gives the window a traditional appearance, the grid lacks dimension and won’t cast shadows like a true divided light window.
A step up, architecturally and in price, is to apply a real wood grille overlay on the interior surface of the glass sash. The single overlay gives the window some architectural relief, but light shadows will still differ from those of true divided windows.
The best SDLs offer architectural wood grilles on both exterior and interior glass surfaces. These double wood grille overlays come closest to the appearance of through-the-glass muntins at a cost 10–30% cheaper than TDLs. A good double grille will also reflect the different profiles found on the interior and exterior parts of the muntin.
In the less expensive option of the two, the back of the grid overlay is applied with a bonding tape in black or a dark shade to enhance the shadow effect of the applied muntin. In a step up, aluminum spacer bars are inserted inside the two glass layers to enhance the sense of a true divided light.
The most expensive option, by far, is a true divided light, with a wood assembly holding individual pieces of glass in place. The high cost comes from engineering individual units for each “pane” that look like traditional windows in factories set up to make windows in a completely different way. A single 12" x 8" double-glazed light, for instance, can be composed of dozens of different parts, from the individual panes of glass to multiple pieces of wood, plus hidden components meant to stabilize the structure and keep it weather-tight.