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What U and SHGC is needed in temperate weather conditions to achieve NetZero?

kbretz | Posted in Energy Efficiency and Durability on

In this wonderful community, Energy Efficiency is often been in reference cold climates. I live in California and am in the architectural stages of building a NetZero house.

We have two seasons: Summer and Rainy. The rainy season lasts from November to end of Feb and during those months it can actually freeze – although I doubt if we ever have more than 5-6 freeze days a year. In the summer we never have more than 5-6 days above 90 in a year. We probably have at least 330 days of sunshine.

So all in all, pretty temperate weather – although regardless of the season it does cool down in the evening – even summers require sweaters in the evening. We do have wonderful weather – but it is not the weather I am writing about but what kinds of U factor and SHGC should I be looking for in windows as I try to achieve NetZero.

Of course I am going to do roof over hangs on the south side but should I be looking for the same U and SHGC on the windows on all sides of the house? I assume not. Is there any enlightenment anyone would be willing to share with me? When it comes to walls I am trying to achieve an R-30


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  1. GBA Editor
    Martin Holladay | | #1

    In your mild climate, you can successfully build a net-zero house with a wide variety of window options. If I were you, I would buy double-glazed windows with a low-e coating.

    I would aim for a whole-window U-factor of 0.30 or so. While your south-facing windows might have a somewhat higher SHGC than your west-facing windows, you probably want low-solar-gain glazing for the east and west sides of your homes -- which means that you want a whole-window SHGC of 0.28 to 0.40.

    For more information, see All About Glazing Options.

  2. Expert Member
    Dana Dorsett | | #2

    Since this is a new design, you can play "what if" games with it using BeOpt to find the best balance between higher-R in other assmblies vs. lower-U and optimize the SHGC by which direction the window is facing. In most of CA you could even hit Net Zero with code-min windows, and 1.5x better than code min on wall & attic R, provided you have optimal sun and with an optimally pitched roof. But the number of corners and the pitch/color of the roof etc all play a role here.

    You can hit Net Zero on a tent with 1-layer plastic windows too, if it's a big enough roof, but most people wouldn't take that route: :-)

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