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DO SKYLIGHTS BRING SKY HIGH ENERGY BILLS?
September, 2018

Dear Pat, Our kitchen and dining room need daylight!  We’ve been thinking about putting in a skylight but we’re wondering if that will increase our energy bills. Any advice? - Monica

           

Dear Monica,

Skylights can bring a little of the outside world indoors and make your living space more livable—when they are placed and installed correctly. But they can also have some impact on energy bills and comfort, so you’re taking the right steps by doing some research ahead of time.

A downside of skylights is that they are a source of heat gain in summer and heat loss in winter. The amount of impact depends upon a number of elements including its energy rating, size, placement and quality of installation. You can find out the energy efficiency by looking at the skylight’s NFRC Energy performance label, which shows four important pieces of the energy efficiency puzzle:

  • Insulation value (U-Factor)

  • Ability to transmit solar heat (Solar Heat Gain Coefficient)

  • Ability to allow light to transfer (Visible Transmittance)

  • Air leakage.(1)

 

Finding a unit with the best ratings in all these categories will help maximize your skylight’s energy efficiency and performance. It’s probably worth spending more on a better product, since professional installation takes up the lion’s share of the cost of putting a skylight into an existing roof.(2) That said, even the best skylight has a much lower insulation value than a properly insulated attic.(3)

Just as important as finding the best skylight is determining the proper size, number and placement. You want adequate light, but too much light can make a room less functional on a bright day.  Skylights on a steep, north-facing roof will reduce the unwanted solar heat gain in the summer, but this also reduces the desirable solar heat gain in winter.(4)


Ultraviolet (UV) light can cause furniture finishes to fade. This can be minimized by making sure your skylight has high-quality glazing or by applying a special film to the skylight.(5)

Proper installation by a knowledgeable professional is essential to avoid all-too-common problems. One serious issue is water leaks—a problem often caused by improper exterior installation on the roof.  Flashing must be installed correctly to be effective for the pitch of the roof and the type of roofing.

Another potential problem area is the skylight shaft that transmits the light from skylight into the living space below. Inadequate or poorly installed insulation is a source of heat loss, and can cause ice dams that allow water to find its way into the home.(6) Air leaks in the shaft can also cause these kind of problems.  Moisture problems can cause condensation build-up inside the home, resulting in mold, mildew and rot (especially in bathrooms)(7).

An alternative to the regular skylight is the tubular skylight. A small skylight on the roof is connected to a flexible tube that runs through the attic to a room below. This system provides a diffused natural light.  The tube is much smaller than a skylight shaft and is easier and less expensive to install.  The tube has less heat loss, and is less leak-prone.(8) Tubular skylights can fit into spaces that a traditional skylight can’t, and can be a much better choice in rooms with high moisture, like bathrooms, saunas or indoor swimming pools.(9)


As you consider your skylight decision it may be worthwhile to go back to your goals. Maybe you can have more light in your room without a skylight—and save money in the process—by trying these steps(10):

  • Paint the room a lighter color

  • Hang mirrors

  • Replace heavy window coverings with lighter ones

  • Add indirect lighting such as upward-facing pole lamps

  • Trim any trees that shade the windows

 

If you’ve done your research and decided to move forward with new skylights, I hope you buy the best product your budget will accommodate, and find a contractor with experience and solid references to provide the installation. Good luck!

For more information on skylights, please visit the September 2018 more information page.

 

Footnotes

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Too many or too large skylights and windows can make a room too hot in summer and too cold in winter. Photo Credit: NREL/DOE.