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by Dr. Oneida Cramer

Genesis of the sunroom came from the greenhouse, according to J.P. Bains, general manager at Four Seasons Sunrooms. Long before the solarium and sunroom industry and the green house industry, there was glass--a clear substance that?s been in use for 5,000 years yet only recently revolutionized for residential windows.

Around 30 A.D., the Roman emperor, Tiberius built one of the first known green houses by fabricating and assimilating tiny translucent sheets of mica, a formidable task?all to satisfy his craving for fresh cucumbers. But not until 1599 did Jules Charles, a French botanist, build the first practical greenhouse. Used for growing medicinal tropical plants, the greenhouse was located in Holland, and the idea spread quickly throughout Europe. The French especially loved the newly discovered orange fruit, and so built greenhouses called orangeries to protect the trees from frost. In America, George Washington had a pinery built at Mt. Vernon to grow pineapples. Today, nearly 3 million hobby greenhouses exist in the US, according to And that number is expected to grow.

Yet, greenhouses have given way to sunrooms, solariums, and conservatories.

?The garden room with a solid roof became popular in the mid 1980?s, said Bains. At that time, people wanted solariums with glass roofs; they just couldn?t tolerate the heat. For clear glass transmits most of the sun?s energy wavelengths, which include the short ultraviolet waves, the medium visible light spectrum, and the longer heat radiant wavelengths. Then came the development of high performance glass products, which made the window more of an ?energy filter,? capable of transmitting selectively and reflecting different energy wavelengths depending on the characteristics of the transparent portion of the window.

Scientists at the Massachusetts Institute of Technology conceived the idea that a fine metallic coating on glass affected its transmission properties. (Aside, it?s well known in biology that opposites attract. Likewise negative charges and positive charges are also attracted to each other). By negatively charging the glass surface and positively charging the metal oxides during the glass manufacturing process, metals penetrated the glass surface and formed a barrier to specific wavelengths of light, primarily the longer heat wavelengths and the shorter UV wavelengths. First introduced in 1981, this glass called ?low-e,? which stood for ?low-emissivity,? looked clear and transmitted the light spectrum. But low-e glass also retarded heat build up, especially when used in double pane windows. For example, the basal thermal units per hour per square foot (BTU/HR/SQ FT) of measurable heat build-up from a single pane of glass (213 BTU/HR/SQ FT) was reduced to 182 BTU/HR/SQ FT with two glass panes and further reduced to 170 BTU/HR/SQ FT when one of two panes was low-e glazed glass, according to Four Seasons Sunrooms manufacturers? specifications.

In 1993-94, Four Seasons began marketing a new line of products impregnated with up to nine separate layers of metal, including silicon nitride, titanium nitride, zinc oxide, and low-e silver in 33 different combinations. The glazing material added only 0.00000484 inch of surface space to the 1/8-inch piece of glass. Yet, two or three panes fused together with inert gas such as argon or krypton between the panes was almost as effective as a solid structure in retarding heat build up. For example, a triple glass/ krypton gas combination (MC-22/krypton/MC-56/krypton/clear glass) reduced heat gain to 22 BTU/HR/SQ FT, which was just slightly higher than 12 BTU/HR/SQ FT, the measurement with an insulated aluminum surface, according to Four Seasons manufacturer?s specifications. Such profound insulation, however, allows only 14% penetration of the visible light spectrum.

Yet, highly insulated glass products expand the homeowners? options when constructing sunrooms made completely of glass. For instance, where exposure to sunlight can cause heat build up, such as ceilings and the upper western walls, the recommendation is for glass with lots of insulation. Glass with moderate insulation and better visual transmittance works better on walls that receive less direct sunlight. Note that all windows resist breaking on high impact, such as kicking or flying objects.

So, why shy away from creating a homey greenhouse, especially if you love to look at the view or you love to bring plants indoors. Consider converting a room into an elegant conservatory near an entryway. Call the room your summertime gateway to the garden or your winter repository from frost--bite. But add a separate air-conditioning and heating unit for the best climate control, said Bains.

You can adapt almost every room in the house into a sunroom. Here are a few unusual ideas. In the kitchen and breakfast area, ovens, wall cabinets, and dining room buffets form natural barriers of privacy to the outside world and allow the glass ceiling to take on the appearance of an expansive skylight. And how about converting a music room into a sunroom? Glass not only makes walls acoustically reflective, glass makes the music making experience visually beautiful. Yet, highly insulated glass should be used to prevent the sunlight or temperatures from damaging musical instruments like the piano. Similar caution to protect upholstery and carpeting from fading should also be used. Homeowners might also consider adding solid weatherlock roof panels or a combination of glass and roof panels to reduce the overhead sunlight.

The bath makes a rather unusual sunroom; with mini-blinds for privacy, the bath can be quite cozy. In fact, blinds can be added to all sunrooms, especially the family room, one of the most accommodating in the home to make into a sunroom. Now don?t forget the hobby greenhouse, conventional and freestanding, or perhaps attached to the house.

The many design options available with insulated glass just piques the imagination. But consider costs as well. The manufacturer provides a list of pricing expressed in terms of up-charge over clear glass. For example, a double windowpane (MC-56/argon/clear glass unit), which allows 79 BTU/HR/SQ FT relative heat gain and 56% visible light transmittance costs $13.32 per square foot more than clear glass; a double-pane (MC-22/argon/clear glass) allowing only 30 BTU/HR/SQ FT heat gain and 22% visible transmittance costs only slightly more, $15.75/SQ FT over clear glass. The triple pane unit (MC-56/kryptonMC-56/krypton/clear glass) with 56 BTU/HR/SQ FT, and 35% visible light transmittance, costs $20.59/SQ FT more than clear glass.

So, seek guidance when designing a sunroom or choosing glass window products to find the best solution to meet your needs.

-by Dr. Oneida Cramer
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