Question:
I want to replace some old single-pane first-floor windows with glass-block windows for security. Are they as efficient as other new windows? Can they be opened? Can I install them myself?

Answer:
Glassblock windows are an excellent alternative to standard pane windows for first-floor and basement windows when you have security concerns. Although it’s possible to break through them with a sledgehammer, would-be thieves are unlikely to do so.

Glass-block windows’ energyefficiency will be better than the best-quality replacement paneglass windows. Glass- or plasticblock (which looks identical to glass) windows will have double the insulation value of the old single-pane windows. Glassblock 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 versions are hollow. Two halves are fused with heat and pressure. As they cool, a slight vacuum is created inside, which improves the insulation level.

Commercial-quality solidglass blocks also are available for ultrahigh security but are heavy and expensive.

Plastic-block halves made from acrylic are not fused with heat. The most energy-efficient versions include a thin layer of metal atoms on the inside surface. This creates efficient lowemissivity properties similar to standard replacement paneglass windows, and it saves energy year-round.

Several options exist for opening glass- or plastic-block windows for ventilation. Several blocks can be replaced with a small hopper-style window that opens but is too small for someone to crawl through. Also, the clear panel is made of polycarbonate bulletproof glass, so it’s almost impossible to break through.

Another option is to install a casement-style glass-block window. Similar to other replacement windows, it is custom-made to fit in the old window opening in the wall. The installation of the glass-block casement is similar to that of other windows — an ideal situation for the do-it-yourselfer.

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