Plan the Perfect Sunroom Addition

Your sunroom should be oriented so the glass faces as close to true south as possible.

Think of a sunroom, sometimes called a sunspace, as a productive living area in your home with different benefits in different seasons. In spring and summer, a sunroom provides a relaxing living space. In winter, it’s also a great place to grow food plants. Even better, a sunroom can help heat your home! I estimate that a well-designed sunroom addition can pay for itself in less than five years through savings on food and home heating.

To realize the full benefits from your sunroom addition, you’ll need to incorporate the basic elements of passive solar design: orientation, glazing, thermal mass, insulation and ventilation. If you apply these principles, you shouldn’t need to heat or air-condition your sunroom — you will be able to keep this living space at a comfortable temperature by using natural systems.

Would a sunroom work for your house? If your solar exposure gives you at least four hours of sunlight around midday in midwinter, the answer is probably yes! The sunroom design strategies described in this article will work in almost all U.S. climate zones and southern Canada. However, you may want to research beyond the level of detail presented here to fine-tune your design for your specific climate, especially if you’re trying to optimize your heating potential.

Site Your Sunroom

You will want to orient your sunroom toward “true south” (which is usually a few degrees different than “magnetic” south) to best take advantage of the sun’s low angle in winter. There are several methods for finding true south. In general, orienting the solar window 20 degrees off true south reduces your solar gain by only 4 to 5 percent. On the other hand, if your glass is oriented 45 degrees off true south, solar gain will be 18 to 22 percent less.

Think About Glass

There are several types of glazing you can use for your sunroom, but I recommend glass because it traps more heat energy than plastic and because it’s durable. Plastics do not work as well as glass for trapping long wave heat energy, polycarbonates can scratch and yellow over time, and films are just too fragile for a house.

Dual glazing should be used in all but the most temperate climates, such as southern Florida. In colder climates, including much of the Northeast and northern Great Plains, triple and sometimes even quadruple layers of glass work best. I recommend clear, uncoated glass for sunrooms. Avoid reflective glazings and the newer low-e glass because they prevent much of the solar energy from entering through the glass, and they reduce the solar spectrum. If you want to grow plants in the back area of your sunroom, I also recommend skylights to bring in overhead sunlight.

For optimum winter collection of light and heat, sunroom glazing should be tilted so it’s perpendicular to the sun’s angle at winter solstice (Dec. 21). However, for several practical reasons, I’ve selected vertical glazing for my ideal sunroom design. Believe me, I’ve tried the tilted glazing on sunrooms, and it’s not the best choice for a living space.

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