Image Credit: Energy Vanguard
More Building Science
Everyone loves skylights. Right? They bring so much light into a room they can turn a Seattle kitchen into a bright and sunny Florida room. Especially at this time of year (in the northern hemisphere), having that extra light can brighten even the darkest days of winter.
But skylights have a dark side, too. If you’re not aware of that when incorporating these roof windows into a home, you can end up with high energy bills, rooms that are unusable at certain times of the year, or expensive repairs due to moisture problems.
The benefits
Of course, the main benefit of having skylights in a home is all the natural light you get from them. This is mainly for winter because that’s when we have less overall exposure to the natural light our bodies crave. Nobody likes being holed up in a dark, dim, artificially lit cavern on those overcast winter days when the sun sets shortly after it rises. (Well, maybe with the exception of video gamers and college students who are trying to sleep during the day.)
A well-placed skylight or two can make the difference between feeling OK about yourself on those dark days or becoming a psycho killer. (Qu’est-ce que c’est?) For those who suffer from Seasonal Affective Disorder (SAD) and can’t spend time outdoors, being in well-lit interior spaces can make all the difference.
If you live in a cold climate, you can also get some solar heating from a skylight. To do so, you’ll need to make sure that you get one with as high a solar heat gain coefficient (SHGC) as you can. (The SHGC tells you how much solar heat gain you’ll get from a window or skylight. It’s generally a number less than one, with lower…
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10 Comments
Never again
Allison,
As a builder who used to love skylights for all the reasons you mentioned, I now believe they are simply wrong for the average homeowner, unless they are retired or work from home. As a builder of entry-level homes that were most often bought by young families, it finally dawned on me that nobody was benefitting from the natural light. And in the winter, here in CZ5, they were R-1 holes in R-38 roofs. When considering the lifestyle of the go-to-work, go-to-school family, they were leaving home in the dark and coming home in the dark in the coldest months of the year. Meanwhile the skylights were losing heat all night long when they were home. Far better to have a high efficiency window at R-3+ in an R-20 wall, plus one actually might enjoy a view! Skylights in schools, offices and workplaces, on the other hand, make all the sense in the world. That's where most of us spend our days when the sun is shining.
Response to Kim Shanahan
Excellent point about timing, Kim. That's yet another reason to avoid skylights. Also, I mentioned the difference between wall and window R-values but forgot to point out the difference between ceiling and skylight R-values. Thanks!
Skylights
For those who may not know. There are U-0.05 (R-20), [NFRC = U-0.13 (R-7.7)] aerogel skylights available (4 'x 4' ~ $1,800) that do a good job of defusing light and all but eliminate that blinding bright glare on bright days. Though they would loose much of their light defusing advantages at the top of a skylight shaft.
Ted
Ted,
Who makes the aerogel skylights? Are they available for residential use?
Response To Brad
When planning for my new home construction I received a quote from a local distributor of Kalwall for a commercial 4'x4' Standard Flat Curb-type S-Line.
https://www.kalwall.com/wp-content/uploads/2015/01/Kalwall-Skylights-Brochure.pdf
Because of the 2 ¼" of aerogel (also available in 4") the transmitted light is diffused in all directions, to distant corners of the room , eliminating the sharp glare that occurs when sun shines through a regular skylight. It must be noted that, also as a result of the aerogel, the visible light transmittance is reduced.
For an installation such as a cathedral ceiling there would be no shaft to block the diffused light. But, if installed at the top of a shaft, the glare of the incoming light would be eliminated but the advantage of the diffused light reaching the corners of the room would be lost.
In my opinion, there would be little or no disadvantage, and probably an advantage, to installing this type of skylight on the sunny side of a roof.
Also please note I have no practical building experience. I have neither installed nor used the skylight I noted above, though I have seen a Kalwall aerogel skylight in use in a commercial setting. I do believe that the one that I indicated above could have a good residential use in the right application. I just wanted to bring it to the attention of GBA readers. There are other shapes (pyramidal & domes) and many sizes available but they would have very limited residential appeal.
I have three regular skylights in my current home and they provide much needed light in what would otherwise be darkish areas. There is however much glare when the sun comes directly in; gentle but cool downdrafts occur directly under the skylight shafts (actually kind of nice for sleeping under the one directly over the bed); occasional condensate drips on very cold nights; and they are undoubtedly energy sinks. I believe the Kalwall would maximize the benefits of skylights while minimizing their liabilities.
I'd like to hear Dr. Bales opinion.
Note: Because my circumstances would've required a lengthy skylight shaft, I ultimately elected to use two appropriately spaced commercial 22" solar tubes.
skylights as an early warning signal
I was happily sleeping when awakened by a bright, flickering light shining through the skylight above my bed. If it had been the house on fire, it would have saved my life. As it was, I got to see the Northern Lights:-)
Solar Tubes?
Maybe you could discuss Solar Tubes too. They often seem over sold.
In praise of skylights
I have used many skylights in a number of building projects and never had a negative result. Make sure you choose a skylight with a quality flashing system such as Velux. I have never had a skylight leak, and have reroofed around existing skylights with great success. I use some ice and water shield as a sort of subflashing when roofing around skylights and this works well. Skylight shafts in truss rafter roofs can be insulated with several layers of rigid foam right to the bottom side of the roof sheathing. This forms a highly insulated and airtight shaft.
On the energy side:
Will the skylight replace some electrical lighting use during the year? I have installed skylights in homes and they have been transformational in terms of natural lighting. I like operating skylights that can be opened in the summer to provide a stack effect cooling that will only come with skylights. This takes the heat right off the ceiling and allows cooler air to flow in lower in the building envelope.
Doug
You are right. Light from above can often really transform a space. The question becomes are skylights better than roof lanterns or monitors at doing this?
'Solar Tubes'
Definitely oversold. They can give useful light in a room totally without windows like a walkin closet but a simple LED fixture would be far more energy efficient. The tube is a 24/7 heat transfer mechanism which gives no light at night and light you won't be using most of the day. The LED burns a few watts only when you need it.
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