What Are The Lines On Some Windows Called And What Are They For?

Grid-like windows add a certain charm to homes today, but in older houses they were very much a necessity. For much of architectural history dating back to the 17th century, it was just not possible to make a pane of glass large enough to cover a window opening. The lines that you see on some windows are known as muntins and mullions. These worked together to create a framework for installing larger windows in buildings and homes. Essentially, windows were made up of small sheets of glass held together by strips called muntins. Typically made of wood, muntins run horizontally and vertically and act as frames that secure individual window panes. On the other hand, mullions are larger bars that support multiple window sections across a greater opening. In simpler terms, the real difference between window mullions and muntins is that the latter are small strips that frame small glass panes, while mullions are larger bars that support multiple window sections. 

Today, it is much more economical and energy efficient to install large panes of glass for windows. Mullions are still widely used to support large windows and can serve as design elements.  Muntins are no longer necessary in the construction of windows, but they absolutely still have a place in home design. Today they're more commonly known simply as grids or grilles, and they are a matter of personal preference. They also preserve the charm of homes that are traditional or historic in aesthetic, such as farmhouse, colonial or prairie style.

There are several types of window grids on the market today. Integral Light Technology (ILT) grids are attached to the interior and exterior sides of the glass, with spacers installed to give the appearance of individual window panes. This style lends all the classic old-house charm without sacrificing energy efficiency. Simulated Divided Light (SDL) grids are similar, but are bonded directly to the glass without the use of spacers. Grilles Between the Glass (GBG) are strips that are sealed between the two panes of glass, which look like muntins but with a smooth glass surface that is much easier to clean. Not only can homeowners choose their style of grid, they can also choose colors, grid patterns, and materials. There are even DIY options using a grid kit that can take sliding doors from builder-grade to custom-made. 

When considering installing or renovating your windows with grids, there are a few things to keep in mind. Grids visually improve the curb appeal of many homes, and with all of the customization options, can provide an opportunity to make your house stand out. However, grids that are installed on the outside of the glass can be challenging when it's time to clean your windows. Plus, if the landscaping outside the window is part of a home's appeal, grids can impede the view. On the downside, grids are also another component that can wear out or break over time, which can increase your overall maintenance costs.