Do skylights create sky-high energy bills?

We’ve been thinking about installing a skylight to add more natural light, but will it increase our energy bills?—Monica

Skylights can bring a little of the outside world indoors and make your living space more livable—when they are installed correctly. But they also can impact your energy bills and comfort level.

One downside of skylights is they can add heat to your home during the summer and cause heat loss during the winter. The amount depends on elements like the skylight’s energy rating, size, placement and quality of installation. You can check the energy efficiency by looking at the skylight’s energy performance label, which shows its insulation value, ability to transmit solar heat and transfer light, and its air leakage (see NFRC.org).

Finding a unit with the best ratings in all these categories will help maximize the skylight’s energy efficiency and performance. It’s probably worth spending a little more on a better product, since professional installation makes up the lion’s share of the cost of adding a skylight to a roof. That said, even the best skylight has a much lower insulation value than a properly insulated attic.

Avoid problems by having a knowledgeable professional install your skylight. Improper installation—at the roof, the skylight shaft or the insulation—can cause water or air leaks, heat loss and ice dams. The resulting moisture problems can cause condensation buildup inside the home, resulting in mold, mildew and rot, especially in bathrooms.

The right light

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

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

PAT KEEGAN and BRAD THIESSEN write on energy efficiency for the National Rural Electric Cooperative Association.