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Dear Glass Detective,
I live in upstate New York and want to add a south-facing solarium addition to my home. Because it is south facing, it will not have any shade. It will be small—approximately 6-feet wide by 11-feet long. The solarium will feature glass sides and a glass roof. I’d like to use it year-round. Good visible light transmission is important so that I can see outside clearly. There are a lot of glass options: SolarBan 60 from Vitro, SunGuard High Performance, etc. I’m not sure what the best combination of U-factor and solar heat gain coefficient (SHGC) would be. What are your thoughts?
Thank you for making contact with the Glass Detective with your concerns over how to choose the right glass product for an all-glass solarium you are preparing to build. Your concerns are valid because you state that the solarium will face south and that no shade is provided. Plus upstate New York is no slouch in the winter weather area, so insulating properties will be important. You also state that you would like to be able to use the solarium year-round. You have obviously done some upfront research because you understand the needs for good visible light transmittance while also getting a good SHGC in combination with an acceptable U-factor (a measure of heat transfer/loss or gain). Lastly, you refer to two types of glass that you have researched— Solarban 60® (a product made by Vitro Glass) and SunGuard High Performance® (a Guardian Glass product). My compliments on your investigation to date.
My direct responses to your questions (along with a few comments) are as follows:
Also, you’re going to have to come up with a balance of what you will accept regarding visibility and heat gain control. These two factors sort of oppose each other in some settings. To improve heat gain performance, you may have to give up some visibility and vice-versa. There are trade-offs and you may have to make some compromises during the glass selection process.
Solar Heat Gain Coefficient (SHGC): The percent of solar energy (direct and indirect) that is transferred to the indoors through the glass in a given opening. For a baseline, we will use a single piece of 1/8-inch (3mm) untreated clear glass and it has an assigned SHGC of .86.
U-Value/Factor: A measurement of the heat gained or lost through glass based on the difference between the temperatures on either side of the glass (indoor/outdoor). The lower the U-Value, the better the insulating performance. Sometimes people would like to know the “R” Factor (another measure of heat/cool transfer resistance) and this number is actually the reciprocal of the U-Value. So a U-value of .28 has an R-Value of 3.5714.
Light Transmittance: The actual percentage of visible light going directly through (transmitted through) a piece of glass.
Let’s take a quick look at some examples. The following will all be a 1-inch insulating glass unit (2 lites of ¼-inch glass with a ½-inch air space in between the 2 lites) and a SunGuard Super Neutral® Coating (SNX 62/27):
|Clear (both lites)||64%||.29||.27|
|Lt. Gray |
(w/1 pc. laminated)
These values are taken directly from Guardian’s Technical Information publication for its SunGuard® product line. This information, and Vitro’s published performance values, can be found online at their corporate websites as well
The point I am making here is that slight changes in glass types will impact the performance characteristics of the glass. Also, there are numerous variations of the coatings and glass types that are available.
I am going to strongly suggest that you identify and work with a local contractor in your area that has experience with solarium construction. Not only can they help you with design (and there are some standard designs that are attractive and priced competitively- especially when compared to a custom-built solarium) but with budgeting as well. A good contractor can provide glass samples and offer advice based on his/her experience.
In closing, I applaud you for your up-front efforts to get a jump start on these glass matters and I wish you good fortune with your solarium project. And thank you again for reaching out to the Glass.com Glass Detective.
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