Glass block windows and double pane windows are very different window options. The most obvious difference is visibility: double pane windows are designed for visibility and very clear views of the outdoors. Glass block windows are typically designed for privacy and obscure views from the outside in, letting light through but obscuring visibility.
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Glass Block Windows
Glass block windows are made of very thick pieces of glass that are cemented together and bonded to the frame as one entire window. Traditionally, most glass block windows are made out of perfect squares of the glass material that are patterned together. There are two types of glass block windows. The first is a panel version, where the glass blocks tend to be thinner and are installed in a single pane at a factory, then shipped in various sizes. The second option is a window pieced together of individual glass squares, usually thicker than the panels, on site.
Double Pane Windows
Double pane windows are simple classic windows that have two panes of glass. The glass is clear and can come in a wide variety of sizes and designs. Sometimes there is air between the two sealed panes, and sometimes the space is filled with an inert gas that helps reduce heat transfer between the indoors and outdoors.
Glass block windows are used mostly for decoration. The squares can be either colored or clear, but their thickness decreases visibility significantly. Some glass blocks have different wave or frost patterns that make it even more difficult to see through. Double paned windows can take the place of any traditional windows and provide an unobstructed view. Their appearances depends on how the frames are constructed.
Overall, glass block windows tend to be less expensive than double pane windows. The added features of double pane windows raise their price to an average of $600, while glass windows cost only $150 to $200 for a similar pane. However, there are many factors. A hand-installed glass block pane, mortared square by square, may be more expensive than the cheapest kind of double pane windows.
Double pane windows provide room for many different types of energy-saving features. They can be filled with an inert gas, they can be framed with fully sealed materials, and many different protective coatings can be applied to keep UV light out. However, glass block windows are very thick and tend to naturally keep warm air out of the house. Energy savings are often equal, although superior in higher-end double pane windows.