Glazing is clear or translucent materials that allow sunlight to penetrate and warm the room. Glass is the most common glazing material, and many sunspace developers choose glass for its durability, clarity, and appearance. But plastic glitter may be cheaper, stronger, lighter and easier to work with, making them popular choices with 20% of homeowners who build their own sunspaces. Some plastics even transmit solar energy more efficiently than glass. On the negative side, plastic scratch easily, expand and contract more during extreme temperatures (which makes them harder to seal), and generally less durable than glass.
Determine whether glazing to use, is only the first step in decision making, however. Advances in glazing technology allow designers to tune performance by choosing glitter to meet the specific needs of their projects.
Historically, manufacturers have used multiple layers of glass to improve the insulating value of a window. Besides making the device more energy efficient, extra layers of glass also increased weight and bulk and price of the device. But today’s low-emissivity (low-e) coatings-thin, invisible metal or metallic oxide film has revolutionized the glass industry.
Low-e coatings applied to the surface of the glitter or a film suspended in air between the panes of glass. They reduce radiant heat loss and gain and dramatically improves 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 the windows with less than 70% visible light transmittance can support plant growth.
When argon, sulfur hexafluoride, carbon dioxide or other gas filled with higher insulating value than air is included between the glitter, energy efficient windows are further improved. Although the extra layers of glazing and low-e coatings lower total light transmittance anything, the reduction is more than offset by the increased amount of heat back into space. Other new window technologies include spectrally selective coatings (the next generation of low-e films), which rejects heat while procedure lights, electrochromic glitter to facilitate and darker as small electrical currents are applied and removed, and “super windows” to assemble a range of functions (eg, low-e coatings, gas fills and insulating frames and spacing blocks) in one unit.
If you decide to use overhead glazing in the roof of your sunspace, invest in one of the glazing systems designed specifically for this purpose. Overhead glazing has a reputation for leaking, but excellent closures are now in the market. Invest in a good system, it is not a place to cut corners. In some areas, building codes require you to use plastic or tempered or laminated glass in overhead and sloped glazing sections for safety reasons.
Which glazing system best suits your project depends on your budget and the climatic conditions of your site. For more detailed information on current and future glazing options, contact the Energy Efficiency and Renewable Energy Clearinghouse (see Source List).
Water is the most effective thermal mass, because it holds the most heat per unit volume. Anything that will not leak will work to keep water and designers and homeowners have used everything from plastic jugs to 55-gallon (208 liter) drums with specially designed (and often very attractive) containers.
Masonry materials (brick, concrete or stone) are also good opportunities for thermal mass. Although they retained only about half as much heat as water, they can also support the structure, form the floor of the compartment and serve as a wall between the house and sunspace. Masonry is most effective in 4 – to 6-inch (10 – to 15-centimeter) thickness. If the walls are built with concrete blocks, the holes in the blocks should be filled with concrete.
The surface of thermal mass materials should be dark colors of at least 70% absorptance. Variety has about a 95% absorptance rate, Deep Blue has about 90%, and dark red around 86%. Nonstorage materials should be lighter colors, so they will reflect light to the thermal mass does not lie in the sun. Thermal storage materials can be placed in the floor and in the north, east and west walls of sunspace.
When masonry floors and walls are the only thermal storage materials in space, 3 square feet (0.3 square meters) of 4-inch-thick (10-centimeter-thick) masonry surface per square foot of south glazing is probably sufficient. When the water in containers is the only heat storage medium is used, recommended ratio is 3 gallons (11.3 liters) per square foot (0.09 square meters) of glazing. These are only rules of thumb and should be confirmed by modeling your project on a computer or control of a design or construction professional in your area who are familiar with local design practices.
To maximize comfort and efficiency, it is important that your sunspace be well insulated. Sunspace perimeter of the foundation wall or slab track should be isolated down to the frost line (ie the depth to which frost penetrates the soil) and under slab track, if appropriate in your area. If you live in a very cold climate, isolate the east and west walls of sunspace rather than glazing them. Always isolate parts of the exterior walls that are not glazed. Check with solar specialists in your area or the resources cited in the source list for guidance on your project.
Although overhead glazing can be beautiful, an insulated roof provides better thermal performance. When the biggest part of the structure is well insulated, heat loss in winter is reduced and the summer sun will not strike the inner wall and cause overheating. Instead, skylights can be used to provide some overhead light for the plants. And if they are the type to open, skylights offer a way to vent excess heat. Skylights are available with advanced glitter to reduce radiant heat loss to the night sky.
Window coverings, shades, and other forms of movable insulation to help trap the warm air in sunspace both after the sun has set and in overcast weather. When closed during extremely hot days, window cleaning surfaces can help keep sunspace from overheating.
Thermally isolate sunspace from the house at night is important. Large glazed, French doors or sliding glass between the house and sunspace will maintain an open feeling without the heat loss associated with an open space.
Overheating can kill plants and make sunspace unlivable. Controlling overheating, some designers place operable vents at the top of sunspace where temperatures are the highest and at the bottom where the temperature is lowest. For times when you’re not home to open the vents manually, thermostatically controlled motors can be installed to automatically open them.
If the passive (ie, nonmechanical) turnover is not possible or practical, with thermostatically controlled cooling fans can be used to circulate air to the rest of the house. Other forms of climate control includes shades or movable window insulation that can be operated with electric timers or sensors.