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What width should soffit overhangs be in order to use oreintation specific glazing?

What is the minimum industry standard for the width of soffit overhangs in order to take advantage of orientation specific glazing for both triple pane windows and slider/patio doors located on the south side of a house? Although I want to take advantage of passive solar heating, I do not wnat the house to be overheated in the summertime. I would like the soffit overhangs to provide adequate shading during the summer here in Connecticut.

Asked by JOSEPH POLAND
Posted Thu, 01/31/2013 - 17:44
Edited Thu, 01/31/2013 - 17:55

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2 Answers

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Joseph,

There's no industry standard (that I've ever heard of, anyway). It's more a matter of the cutoff angle needed to provide full shade across the window or door. But it's not as simple as that, either. The highest sun angle occurs at noon on June 21 - but the majority of the hot summer days occur in July & August, at lower sun angles. A reasonable place to start might be to see what depth you need for full shade on June 21. For CT that'll be approximately 70 degrees from horizontal. Meaning, from the bottom off the glass to the tip of the overhang is 70 degrees up from horizontal. And that's only for true south facing facades. As you turn east and west the overhang will be less and less effective. But overhangs are good for rain management too. Have you considered other types of shades - movable awnings, etc?

Answered by Cramer Silkworth, PE
Posted Thu, 01/31/2013 - 18:15

2.
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Joseph,
Here is a link to a useful online calculator to help you design your roof overhang:
Overhang Design

Other useful tools are listed on this page:
http://www.susdesign.com/tools.php

Answered by Martin Holladay, GBA Advisor
Posted Thu, 01/31/2013 - 18:29

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