Are they as efficient as other new windows, can they be opened and can I install them myself?
Answer: Glass block windows are an excellent alternative to standard pane windows for first-floor and basement windows when you have security concerns. Although it is possible to break through them with a sledgehammer, it is unlikely a would-be thief would attempt this.
Glass block windows will be better, but not as energy efficient as the best-quality replacement pane glass windows. Glass or plastic block (which look identical to glass) windows will have double the insulation value of your old single-pane windows. Glass block windows are as airtight as a wall, so there will be additional energy savings from reduced air infiltration.
Glass blocks appear to be solid, but residential ones are hollow. Two halves are fused together under heat and pressure. As they cool, a slight vacuum is created inside which improves the insulation level.
Commercial-quality solid glass blocks are available for ultrahigh security, but these are very heavy and expensive.
Plastic block halves, made from acrylic, are not fused with heat. The most energy efficient ones include a thin layer of metal atoms on the inside surface. This creates efficient low-emissivity properties similar to standard replacement pane glass windows and it saves energy year-round.
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