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Community and Q&A

Window SHGC?

KrisCurrie | Posted in Energy Efficiency and Durability on

Hi guys, house will be 160 deg. south with 328 sqft of glass south 3′ over hangs on south side.
(3400sqft two story with daylight basement)
total glass 462
pvc triple avg. u value 1.0 shgc .20-.24 , should i go for the higher heat gain? .46? on south windows

thanks kris

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  1. GBA Editor
    Martin Holladay | | #1

    Please tell us your climate zone or geographical location.

  2. KrisCurrie | | #2

    Martin, Atlantic Canada. Zone 6

  3. GBA Editor
    Martin Holladay | | #3

    You live in a relatively cold climate. According to the recommendations I made in an article I wrote in 2010 (All About Glazing Options), south-facing double-glazed windows in a cold climate should have a SHGC of 0.42 to 0.55, while south-facing triple-glazed windows in a cold climate should have a SHGC of 0.33 to 0.47.

    These recommendations were based on classic passive solar design principles. However, more recent analyses have called these classic passive solar design principles into question; to learn more about newer design thinking, see Reassessing Passive Solar Design Principles.

    My current advice echoes that of Gary Proskiw: The area of your south-facing glazing should consist of what’s necessary “to meet the functional and aesthetic needs of the building.” There is no need to maximize the area of south-facing glass out of a mistaken belief that a window is a heat-gathering appliance.

    If you follow this approach, the SHGC of these windows becomes less critical, and you may decide to choose low-SHGC glass to reduce the chance of summer overheating.

  4. STEPHEN SHEEHY | | #4

    My house in Maine, zone 6, has a lot of glass on the south side, with 3' overhangs. Triple glazed, SHGC of .49. No overheating issues, summer or winter. In a cold climate, additional heat is usually welcome.
    You might want to think about some shading above the first floor windows if you are worried about overheating.

  5. kenorakq | | #5

    The new advice echos what I heard from a friend who recently built with "a lot of south facing windows.. think chalet style with about 70% glass on the south side).
    He opted for the best performing glass (like that chosen for the north side of the house) with no consideration for SHG. He pointed out that in the winter when SHG is desired the glass has only about 4-6 hrs of decent sun exposure and 18-20 hrs of twilight or dark. He reasoned that the heat loss during the majority of the day couldn't possibly be made up during the brief period there would/could be SHG.
    He opted for tri=pane, low e argon, vinyl windows..I don't know the numbers but they were made by Jeld-Wen in Winnipeg.
    Just my observation.

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