Can a skylight ever be energy positive?
Hello,
I’m curious as to whether skylights are always net losers, or if one could be favorable given the right conditions. In general they seem to be avoided due to the heat gain potential and nighttime loses.
The house is a 1.5 story retrofit with a 10-12 pitch roof facing S-SE, with 75% deciduous shading in the summer. I’m in Minneapolis, climate zone 6, and expect to have R38-42 insulation under the sloped portion where the skylight would be. This would be the only southern light we can get in the upstairs of the house, and would also offer a desirable view from the home office where I spend most of my time. Could a skylight here ever be energy neutral or favorable given the spring/fall/winter heat gain? If so, what specs are most important to look for? Should I just concentrate on high U-value? I have had good luck with Velux, but I’m not sure if they’re considered high performance. In the summer I would anticipate using an internal shade in the summer for the hour or two of direct light it may get. If there is no way winter gains would offset summer gains at higher sun angle, I get that too.
Thanks,
Ryan
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Replies
Ryan,
Q. A triple-glazed south-facing skylight will almost certainly be energy-positive during the winter. For more information on this topic, see Windows That Perform Better Than Walls and Choosing Triple-Glazed Windows.
Just because a south-facing skylight can be energy-positive during the winter, doesn't mean it's a good idea. All of that solar gain doesn't necessarily come on the days when you want the heat. It's easily possible that a south-facing skylight will lead to overheating, even in March. Once summer rolls around, every single BTU of solar gain will be unwanted, and your air conditioner will be working harder than it would if you had never installed the skylight.
South-facing skylights create a lot of glare. It's hard to imagine a worse type of fenestration for a home office.