I am concerned about the security and efficiency of some of my old single-pane windows. I think glass-block windows would be more secure. Are they efficient, and can I install them myself?—Kathy W.
Some people who are concerned about home security are replacing old, inefficient windows with glass- or plastic-block windows. This is particularly true for first-floor and basement windows where a thief can hide and take the time to quietly pry open or break a standard window.
Along with security and privacy, protection from severe weather is also becoming a more widespread concern. Some standard pane-glass windows can withstand wind forces during a violent storm, but flying debris can break through most pane glass.
It is possible for an intruder to break through a glass-block window, but it would be very difficult, take a lot of time, and create a lot of noise. Even though most glass-block windows are hollow and someone may be able to break through a single block, the opening is still not big enough to crawl through.
Plastic-block windows are also available and look identical to true glass blocks. Most are molded from impact-resistant acrylic plastic, which does not yellow over time as other plastic may do in the sun.
Blocks provide insulation
Glass- and plastic-block windows can be energy efficient for several reasons. There is a sealed insulating air gap inside each block. This is particularly efficient in glass blocks because the two halves are fused together under heat. When the blocks and the air inside cool, a slight insulating vacuum is created. Also, just as most replacement windows now use low-E (low-emissivity) coating on the glass to provide insulation, so do glass and plastic blocks utilize low-E technology.
Block windows are also efficient because they remain airtight throughout their life. There is little, if any, air infiltration when the blocks are assembled properly in mortar or clear silicone. When installing a completed block panel, make sure to caulk well around the frame perimeter.
It is not difficult to install block windows yourself; do-it-yourself kits are available. There is quite a learning curve to install individual blocks yourself, so if you are inexperienced, select preassembled panels. These large complete panels are installed much like any replacement window.
Windows with a breath of fresh air
If you want natural ventilation with your block windows, several of the blocks can be replaced with a small hopper window. The opening panel is made from tough, hard-to-break polycarbonate plastic.
Opening casement-style block window panels are often used in bathrooms and basements to provide light, security, and privacy. Check local building codes about escape requirements; many casement-style block replacement windows should meet these rules.