A window muntin is the bar or rigid form of support that separates two panes of glass. Panes of glass that are separated by muntins are technically called “lites” or “lights,” but usually, they are simply referred to as panes. Although paned windows are still common, they generally do not have real muntins between the panes. Instead, the paned looked is achieved by using a single piece of glass covered with a plastic or wooden grid that makes the window look just like individual muntins.
What Causes Muntins to Crack?
Very old homes, usually those built before 1950, used lead muntins to separate window panes. Lead, since it is a metal and a pretty good heat conductor, shrinks and expands according to the various warmth or coldness of exterior and interior temperatures. When it does so, it can crack the glass, warp the frame, or just break.
What Problems Can Result?
Because most muntins are simply thin strips of material, they are subject to the same kind of damage that glass is subject to—breaking, cracking and snapping. Another common problem with muntins is that they loosen from their original position, creating a “rattly window” problem or loose panes. This also results in poor energy efficiency around the window
What to Do?
Realistically windows with lead muntins are just too old. They are outdated, sound bad from the rattling, look awful and typically cause a number of problems that can be solved with window replacement. If you want to update the look of your home and increase its energy efficiency try thinking about new windows to replace. If you like the muntin look you can get it with new windows as they can have the same appearance but with a better performing window.
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