Is a roof made out of glass viable?

Question

I have thought about that if I am ever going to build a single floor house this is what I would do. I would make the whole roof out of glass (like a greenhouse). This glass roof would be made out of double glass with as much as 20 cm between the two. In this space I imagine that there would be a very dark curtain, which would stop sunlight in the case where the temperature inside the house gets too high (I am living in Scandinavia so this would just be the case for a few months per year). It would be possible to control the ventilation in the space between the glasses by opening sections of the roof.

The positive effects of this would be:

• Watching the stars from bed at night
• Feeling like one is outside the whole day if the curtains are away
• Less need for lighting

A part of the reason for doing this is that light is a precious thing in Scandinavia during the winter.

What am I missing here? Why have I never heard about such a house (bad research?)?

Answer 1

You lose more heat through ceilings than through other surfaces (because the warm air is touching it, and because of good convection currents).

The insulation value of glass is very low. To put it in USA terms, a single pane of glass is R-1, while many house walls are R-20 and ceilings R-30. I've seen superinsulated roofs at R-60. Even triple-pane glass is only R-3; inert gases inside help, but over time they leak; you probably can't have a good seal if you want to run a curtain through them.

During the day, insolation will warm your house through the ceiling (probably too much, even in your part of the world), but at night when you're only losing heat, you'll really feel it. You'll use a lot of energy to stay warm.

At the same time, it would be very expensive. Windows are generally an expensive feature in a house. Sloped windows should be tempered for safety, which makes them even more expensive. And you're talking about a huge area.

Roofs in particular get beat up pretty hard; standard roofs (asphalt shingles) around here last about 20 years.

Meanwhile, you lose the opportunity to put photo-voltaic panels on your roof.

However, you can get a lot of what you're looking for with a much less ambitious approach.

• Small solar tubes bring in a huge amount of light for their size.

• A skylight over your bed can let you stargaze in comfort. Put your bed up high for a wide viewing angle.

• Spend more time outdoors.

Answer 2

As The Evil Greebo states, it's certainly done in many commercial buildings. A great example is the Mall of America, which has a central atrium that has a glass roof.

This glass roof provides enough heat gain in the winter to heat the entire building (with the aid of all the body heat being generated as well...):

Despite Minnesota's cold winters, only the mall's entrances and some below ground areas are heated. Heat is allowed in through skylights above Nickelodeon Universe.

http://en.wikipedia.org/wiki/Mall_of_America

All that said, even though the MoA roof is, overall, flat, the panes of glass are all peaked to handle rain and snow run-off. I don't think you'll find a way to easily build a flat glass roof without a major support grid of some sorts, as the glass itself won't be able to carry the load.

As for never hearing about a house that does this, I'm not sure. Lots of turn-of-the century large houses had glass greenhouses/solariums. An example:

http://www.mnhs.org/places/sites/jjhh/

And on the more modern residential scale, there's all sorts of greenhouse systems, sunlights, etc.

I think the main reason you don't see a full-glass roof aside from cost is that I imagine it's impractical. Sunlight is important, but a full roof would be a glaring amount of sunlight. You'd have to wear sunscreen and sunglasses in doors all day. Kind of makes watching TV difficult. ;)

Plus, in many climates, the heat gain in the summer and/or heat loss in the winter would be impractical.

I'd suggest building a 3/4 season porch/greenhouse. That gives you the option to sleep there when you want, but you're not committed to a full roof on the entire house.

Answer 3

Can you do it? Certainly. Commercial buildings have glass roofs all the time.

I expect you'll pay an extremely higher price for such a roof, however, at every stage. The architect fees alone will be a not to pretty penny since this is non standard.

Answer 4

Greenhouses have glass roofs. However, they also have steeply pitched roofs to shed snow loads; this means more material use and a challenge when building it. And heating in the winter is VERY expensive. So it is technically feasible, but probably impractical for a living space.

Putting a curtain between the layers is asking for trouble. Sooner or later it'll break, and then you'll have to get access.

However, you don't need a whole glass roof to do what you want. Skylights and large windows can provide most of the same benefits. I have a room in my house with windows along two walls, plus four large skylights in a vaulted roof. I can see the stars through the skylights, I can feel the outside through the large windows, and because the windows face south and west I get good light in there when the sun is up. It does get quite hot in the afternoon, but opening the skylights helps with that. You'd be surprised how much of a difference just a few skylights make.

You could also have a small deck where you can lie out in your sleeping bag. ;)

Answer 5

I once lived in a glass-roofed home. I still miss it. I loved falling asleep looking at the stars and the moon and the treetops. The sunshine was wonderful, too. And on the rare occasions when we had snow it was amazing! Diffuse white igloo light- fabulous! Oh but it was impractical...too cold in winter, too hot in summer. And that was on the mild west coast of Canada where the weather is really very moderate. I did occasionally have cause to wonder about safety, too, when it got stormy. The other issue was cleaning the roof...quite inconvenient and yet necessary. So, please, if you see a way past these issues, do let us know. I still pine for that roof!!

Answer 6

In 2010 we built a 300 sqft sunroom addition to the back of our home in eastern Long Island NY. It is all glass and aircraft grade aluminum including the roof. The glass is skyscraper grade glass sandwiching argon gas. The glass is diffuse impregnated with titanium for self cleaning and 9 other substances for UV and heat control. Most of the roof is visibly tinted for extra shade. No layering of adhesives is used only molecular diffusion. That would have been a deal breaker. Bottom line, like another responder mentioned, I now know I can never live in another home without it. Our solarium actually keeps me from considering selling this house. Heating for us has been a good surprise. At first we thought we would need an HVAC but it turned out the worst case scenario of Blizzardy winter nights are met with two electric space heaters from Costco in addition to the wood burning stove in the main house going full tilt. The sliding backdoor of the main house and one window opens into the solarium so heat transfer is encouraged through both.

The stars at night are wonderful but my thing is the rain. Since childhood I've always loved the sound of rainfall against surfaces. But nothing compares to the sound of rain hitting this 300 sqft glass roof. Also the visual spectacle it creates as it beads and runs off is soothing. Thunder and lightning storms only enhance the show for us. A hammock or hammock chair is a must. The misses has permitted me to install a carefully attenuated design home theater that doesn’t encroach on room space. So we can use the room for viewing backyard concert performances (Sting, Adele, Andrea B. etc.) under the ‘pale moon light’. We have main lighting in the room but it is rarely used. There is a backyard spotlight on the second floor that illuminates the entire backyard and also the solarium through the glass roof. It makes for a much softer extremely pleasant atmosphere. Plants are my wife’s thing so about a quarter of the room is jungle, so I guess that makes me Tarzan. The room is furnished with a large comfortable patio weave style sectional set on one side of the space and a small eating nook with four chairs on the other side. The floor is porcelain tiled with a large heated Auskin wool rug for comfort and a large round rug under the eating nook. The vertical glass walls all have thermal curtains hung which help with heat retention when needed and we are still able to close off the main house though we’ve never had to. However I’m sure our heating bill is a little bit higher than before, but not to put too fine a point on it…We don’t care!! Sounds bad I know but at this point we are just plain hooked.

Answer 7

Here is a great video of a great implementation of a great idea: What if you take it to the extreme and wrap your entire house in a greenhouse?

Family wraps home in greenhouse to warm up Stockholm weather (youtube)

The average temperature in Stockholm in January is -3°C (27°F). For Marie Granmar and Charles Sacilotto it can be much warmer thanks to the greenhouse that blankets their home.

“For example at the end of January it can be -2°C outside and it can be 15 to 20°C upstairs,” explains Sacilotto. He was inspired to build a house-in-a-greenhouse through his relationship with architect Bengt Warne who began designing the first Naturhus (Nature House) in 1974*.

Originally Sacilotto looked for an empty lot to build an entirely new Naturhus, but he eventually settled on an old summer house on the Stockholm archipelago. Using Warne’s design, he covered the small summer home, plus an addition, in 4 millimeter glass. The footprint of the greenhouse is nearly double that of the home, leaving plenty of room for a wrap-around garden, and since inside the bubble it’s a Mediterranean climate, the couple now grow produce atypical for Sweden (e.g. figs, tomatoes, cucumbers).

The favorite spot is the glass-covered roof deck. Since there’s no longer need for a roof, the couple removed it and now have a large space for sunbathing, reading or playing with their son on swings and bikes.

Answer 8

I say why not build an entire roof out of glass. Here is a loft in New York City that did just that...

http://www.tabakistribeca.com/sales/158_chambers_PH_1685000/pics.htm

Answer 9

Well if you happen to be either extremely rich or a very clever engineer and a do it your self here is how I would recommend going about it.

Structurally speaking Aluminium oxynitride or AlON is the best clear glass like matterial known to science. It is a ceramic composed of aluminium, oxygen and nitrogen. Think glass with the strength of aluminum. It is new enough that the military is the only mass manufacturer but producing it sounds pretty easy.

Thermally most clear glass like substances will be mediocre at best but if you get a really good seal between several layers and then use a pump to create a vacuum in between you should have a good thermal insulator, but you could do one better than having an insulator.. MIT just came out with a transparent polymer film could be applied to many different surfaces, such as window glass that absorbs sunlight and stores the energy as chemical potential energy that can be released on demand. If you applied this coating to the layers of glass roof and maybe to a hard wood floor you could get really cheap heating at night. Also given the factors at play radiant heating in the floors would be the best and most efficient system.