What is the preferred glazing type for cold climates?
I’ve come across conflicting answers in my preparation for the PPD test. Some sources say LOW-E with low U-factor to avoid heat loss. While some say the higher the SHGC the better, to maximize heat gain into the space during winter. I’m guessing the direction the window faces affects the answer, but when no direction is provided, what should I look for? Is there an overall sensibility I should go with to answer this on the exam?
Thanks in advance.
Hi @carlo_penaflorida ,
I’ll do my best to help!
Everything you’ve stated above is true. For cold climates you want the glazing to have a low U factor. This is because you want less heat transmission through the assembly to keep your building warm in the winter!
You also want the low-E coating (low-emissivity) coating on your windows because it too will help keep the warm in and the cold out. Wikipedia does a better job of explaining this than I can: Low emissivity - Wikipedia
It is also true that in a cold climate a high Solar Heat Gain Coefficient would be beneficial. The higher the coefficient, the more solar heat gain will be allowed by the glass.
The factors above are ideal for cold climates no matter the window orientation.
In general, in the northern hemisphere, southern facing windows will provide you with the most opportunity for solar heat gain. Northern facing glazing provides the most stable and desirable lighting, but the least amount of solar heat gain.
“The Site Planning and Design Handbook” is one of the major references for this exam and can provide you with more in depth information on these subjects if you’re interested!
Hope this helps!
I also found this online guide to energy efficient windows that might help clear things up.
Thanks for the response! It is is good to know that SHGC and U factors do not have a parallel relationship with each other. SHGC can be high, and U factor can be low, and vise versa. They do not have to be the same. The document you uploaded definitely helped.
Also, I believe you meant to say higher SHGC will let more solar heat gain in? or am I missing something?
Glad you found the information helpful @carlo_penaflorida !
Oops! I did mean to say higher SHGC. Thanks for pointing that out! I’ll edit the original post to avoid confusing anyone else.
hi, Just reviewed the document posted - if the main concern is gaining heat in a cold climate, would we consider higher SHGC with a high U value thus solar heat can flood inside.I understood that Low U value will keep the heat out. There is a reference in FBC book but not very clear what to make out of it.
Hi @svan ,
If you want to capitalize on gaining heat I would consider a higher SHGC with a low U value. You still want to keep that U value low so that you’re keeping your heat in your building! Otherwise, you’ll be gaining heat from solar gain but it won’t stay in the building.
Hope this helps!
in the case above would you consider low U value but not Low-E glass?
sorry and hope I am not asking something that has been answered previously.
Hi @svan ,
No worries! It’s a confusing topic and I still get them mixed around in my head.
It’s likely you want a low-e coating still even in cold climates. They type of low-e coating you want can depend on the climate though.
Here’s a few resources on it that might be helpful -
We typically always spec a low-e coating on exterior glass, no matter the climate.
Let me know if there’s anything else I can help with!
just one quick question. I reviewed the SPDH book content page, and also did a search engine but can’t seem to find any information re: windows, low U factor, SHGC, what chapter are you referring to?
Update: I found information in the Sun Wind Light book by DeKay and Brown 3rd ed. Glazing recommendations.
Thanks for the update with the additional resource @svan ! I’ll be sure to add that to my list of recommendations for candidates on this topic
U-factor measures an assembly’s ability to transmit heat through conduction. Since the possibility of losing interior warmth to the exterior would happen through physical contact of the window with the air, we want to limit the U-factor.
SHGC measures how much heat through solar radiation is admitted through the glass. In a cold climate, we welcome solar radiation, so the IECC places either a generous cap or no cap on SHGC for the cold climate zones.
I believe we want to limit U-factor no matter where we are building. This strengthens the building envelope by preventing conductive heat loss when it’s cold and conductive heat gain when it’s hot. The SHGC is more nuanced. Solar radiation varies based on the relationship of the building to the sun, the window to the sun, and whether or not the window has a shading projection.
I work primarily in the southeast (climate zone 3) where the SHGC governs. Contractors will often submit glazing with a compliant U-factor, but we have to reject it because the SHGC is too high. Obviously in our hot-humid climate, heat gain through solar radiation is problematic especially for windows facing south, east, or west and without an overhang.
If we study IECC section C402.4 Fenestration, we can begin to understand when we want to capitalize on solar radiation and when we want to dodge it.