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Sunspace Components
Glazing - Glazing is the clear or translucent material that allows sunlight to enter and warm the space. Glass is the most common glazing material, and many sunspace builders choose glass for its durability, clarity, and appearance. However, plastic glazings can be cheaper, stronger, lighter, and easier to work with—making them popular choices with the 20% of homeowners who build their own sunspaces. Some plastics even transmit solar energy more effectively than glass. On the down side, plastics scratch more easily, expand and contract more in response to temperature extremes (making them harder to seal), and generally are less durable than glass.
Deciding on which glazing to use is only the first step in the decision-making process, however. Advances in glazing technology make it possible for designers to fine-tune performance by choosing glazings that meet the specific needs of their projects.
Historically, manufacturers have used multiple layers of glass to improve the insulating value of a window. In addition to making the unit more energy efficient, extra layers of glass also increased the weight and bulk—as well as the price—of the unit. However, today's low-emissivity (low-e) coatings—thin, invisible metal or metallic oxide films—have revolutionized the glazing industry.
Low-e coatings are applied to the surface of glazings or to films suspended in the airspaces between the panes of glass. They reduce radiant heat loss and gain and dramatically improve a window's insulating value. For example, double-glazed, low-e windows are about as energy efficient as triple-glazed windows using regular glass, but they cost and weigh less. Note that there have been reports that windows with less than 70% visible light transmittance might support plant growth.
When argon, sulphur hexafluoride, carbon dioxide, or other gas fills with higher insulating values than air are included between glazings, the energy efficiency of windows is further improved. Although the extra layers of glazing and low-e coatings lower total light transmittance somewhat, the reduction is more than offset by the increased amount of heat remaining in the room. Other new window technologies include spectrally selective coatings (the next generation of low-e films) that reject heat while admitting light, electrochromic glazings that lighten and darken as small electric currents are applied and removed, and "superwindows" that combine a number of features (e.g., low-e coatings, gas fills, and insulating frames and spacers) into one unit.
If you decide to use overhead glazing in the roof of your sunspace, invest in one of the glazing systems developed specifically for this purpose. Overhead glazing has a reputation for leaking, but excellent sealing systems are now on the market. Invest in a good system—this is not a place to cut corners. In some areas, building codes require that you use plastic glazing or tempered or laminated glass in overhead and sloped glazing sections for safety reasons.
Which glazing system is most appropriate for your project depends on your budget and the climatic conditions at your site. For more detailed information on current and future glazing options, contact the Energy Efficiency and Renewable Energy Clearinghouse (see Source List).
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