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James Dulley

Glass block windows are secure and efficient

Q: Dear Jim: I want security and efficiency, so I might replace some old leaky windows with glass block ones. I also want to use them for decorative interior accents. Is this a good idea and are elastic ones just as good?- Bud W.

A: Dear Bud: Glass or plastic block windows for residential use have come a long way in terms of installation and energy efficiency. They are more secure than standard windows against break-ins and thieves seldom even attempt to enter through a block window. The energy efficiency of some designs surpasses standard doublepane windows.

"Glass block window" has become a generic term for block windows made of either glass or acrylic plastic. People often think that block windows are a solid block of glass or plastic when, in fact, the majority are hollow. There are some solid glass block windows for high security, but they are expensive and very heavy.

In addition to being lighter weight, hollow blocks improve energy efficiency just as the air gap does for standard double-pane thermal window glass. When two hollow glass block halves are fused together under heat, the air inside them contracts as it cools. This creates a partial vacuum to increase the insulation level.

Acrylic block window halves are not fused under heat when they are assembled, so the partial vacuum is not created. To improve their energy efficiency, some solar plastic blocks have a microscopically thin layer of metal atoms deposited on one inside surface. This coating, similar to a low-ecoating on standard windows, reduces the sun's heat flow through it during the summer. This also helps keep heat indoors during the winter.

New glass block windows are now available in lightweight acrylics making them lighter and energy efficient. Security is also enhanced because thieves seldom attempt to enter through block windows.

Some block window designs offer the option of ventilation for efficient cooling and for egress during emergencies. Keep in mind that each room in your home should have a window that will open wide enough for someone to escape through it.

One ventilation option is using casement or hopper plastic block windows that crank open like ordinary windows. Since plastics are less dense than glass, these windows often weigh less than standard double pane glass windows. Most glass blocks are too heavy to be used for windows that open. The frame and hardware would not support the weight.

Several companies produce hinged hopper-style window panels that replace several of the glass blocks in the center of a window. These use double-pane polycarbonate plastic (bulletproof glass). For security, its impact strength is more than 100 times greater than glass. If this is the only window in a room, select a


model in which the entire pane can be removed from indoors for a rapid emergency exist.

Glass or plastic block windows function as natural shades to block the intense direct sun's rays during the summer. This is particularly true of block windows with real mortar or other tinted sealant between the blocks. When the sun shines down from a steep angle, as it does during the summer, the horizontal mortar joints between the blocks act as a louvered shade.

There are several options for installing block windows. The simplest method is to buy complete glass or plastic block windows in a vinyl or insulated frame. The plastic ones, because of their light weight, can be installed with simple nailing fins similar to standard windows.

There are many standard sizes of block window frames available. If you are trying to fit an existing opening, custom-sizes can be made to within one-quarter inch of your window opening. During assembly at the factory, various size blocks are selected and slightly adjusted to the requested size of the frame material.

When installing individual blocks, kits are available to stabilize and space the blocks. One method uses spacers that fit between the comers of adjacent blocks. When the mortar is set, the spacer ends are snapped off and hidden with a little finishing mortar. Another installation kit uses tracks and clear sealant between the blocks. These kits include everything needed and are ideal for the do-it-yourselfer.

Interior, decorative block wall; can be a stunning addition to any home. There are many patterns, angles and colors to provide from a clear view to total privacy. You may want to use a combination of glass and plastic blocks because they look and feel almost identical.

Block walls offer the possibility of using natural lighting in interior rooms because the light from a window will pass through them. An attractive touch is to install efficient fiber optic lighting in the joints between them so the blocks themselves appear to glow.

Write for (instantly download - Update Bulletin No. 497 - buyer's guide of nine efficient designer glass/plastic blocks and do-it-yourself window kit manufacturers listing sizes, colors, patterns, features, prices, and installation instructions. Please include $3.00 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244.

James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.

OCTOBER 2003 19

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