Windows with different sun exposures on same wall — Glazing options
We are planning to build our house with a front porch, but the porch will not run from corner to corner. A room at the corner of the house will have two windows on the same wall, about 5 feet from one another. One will be under the porch, so fully protected from the sun, but the other will be out from the porch so it will be fully exposed. The wall these windows are on will be angled about 40 degrees East of true South.
Since each window will have very different sun exposures, I assume they need different glazing options. Will different glazing options be noticeable on windows so close together? I’ve seen some windows that seem to have a greenish tint to them, which I assume is due to some sort of glazing options. If one window had a slight tint and the other window right next to it did not, I’m worried that would look odd.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
The difference in the glazing selection for those is primarily that you have more flexibility when you choose the ones under the porch roof. The solar heat gain coefficient (SHGC) for the exposed ones matters significantly, but it matters much less for the ones under the porch roof. So likely you could choose the glazing based on the exposed ones and use the same thing all the way across.
Without knowing your climate, I don't know whether you'd want high solar gain on low solar gain for the exposed ones.
A possible exception to my assessment would be if your porch overhang is small enough that you get winter sun on the windows under it but not summer sun. In that case, you might want high solar heat gain windows there even if you didn't want it for the others, in order to avoid summer heat gain. But depending on your climate, you might want high solar heat gain for all of them. And depending on your overhang, you might not get winter sun anyway.
Another possible exception would be if you are in a very hot sunny place and you want extremely low solar heat gain for the exposed windows, and you are willing to reduce the visible light transmission to get there ... but you want the visible light transmission through the porch-shaded windows to be maximized so you get some daylight in despite the porch.
It's hard to give a blanket statement as to whether the look of the coating being different is a concern. It would depend not only on the specific pair of windows you are considering, but also on your sensitivity to small variations like that. Two people could look at the same pair of windows, and one would find the color difference distressing while the other couldn't even see it.
Thanks for the response.
Sorry for not including my zone in my first post. I live in central KY, so it would be Zone 4A. I am assuming I need lower SGHC specs than higher (but that assumption may be incorrect....see the bottom paragraph).
The porch will be the typical depth...8 feet? Based on the orientation approximately 40 degrees to the southeast, the windows under the porch might get direct sun early in the morning in both summer and winter, but I doubt it would be much to be concerned about.
Now that I think about it, I guess the first question I should be asking is whether a house in zone 4A needs to be worrying about SHGC specs on southeast oriented windows in the first place.
Clay,
You live in a mixed climate, with fairly balanced heating and cooling concerns. You probably want relatively low SHGC windows on your southeast wall. For one thing, low-SHGC windows are much more widely available than high-SHGC windows. For another, you will probably be more concerned with too much solar gain in the summer than with too little solar gain in the winter.
Thanks Martin. That's what I assumed, but I have assumed a lot of things along this process and been wrong.
In your article, "All About Glazing Options", I see you recommend SHGC of .28-.37 (whole window) and .20-.27 (center-of-glass) for hot climates. In looking at different window specs, it looks like those numbers are achievable without any "special" SHGC glazing. Do I determine that the "standard" SHGC numbers are good enough for zone 4A and not worry with extra SHGC glazing on some windows and not others, or do I spend the extra money to try to get the SHGC below .2 on those that are exposed, which might risk the windows being noticeably different?
For example, if the basic "Low E4" option of a particular brand has a U-Factor / SHGC / VT of 0.3 / 0.28 / .48 and the option of an extra SHGC coating gets the specs to 0.29 / 0.18 / 0.42, then...
A.) Would that be a noticeable difference in the appearance between two side by side windows?
B.) Would the difference in SGHC specs be cost effective in zone 4A (I guess that depends on the extra cost of the extra SGHC option).
Clay,
My hunch is that the upcharge from 0.28 SHGC to 0.18 SHGC glazing wouldn't be worth it, especially considering the fact that cooling season savings would be balanced by increases in your heating bills.
But the only way to answer the question is to model the house two ways with a sophisticated energy modeling program.
For some back-of-the-envelope estimates, you can play around with the online tool at the Efficient Windows Collaborative web site.