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Community and Q&A

Window shading

hughsdb | Posted in General Questions on

We can easily do shading studies on home designs to determine exactly how much direct sun will come in through each window at any given time on any given day of the year. So what is the algorithm for getting this right? The variables are:
   Sun declination
   The orientation of the window
   Roof overhang
   Distance to the top of the window glass
   Distance to the bottom of the window glass
   Average outside temperature by day and hour
   Distance to, the direction of, and distance out of any side projections.

To this point, I have set days of the year (i.e. June 1 and October 1) when I would allow 10% direct light at 10 am and 6 pm. Totally arbitrary points with no reason beyond a hunch. There must be a more reasoned way of approaching this. Right?

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  1. user-2310254 | | #1


    LBNY has a study on using automated blinds to control energy use ( It contains a diagram for a predictive sun shading algorithm. Is this what you had in mind?

  2. Expert Member
    Akos | | #2

    There are a lot of solar calculators out there. You can try this:

    I have also done solar shade design in Sketchup. You can set up your design, house location and orientation. It gives you a set of sliders for month and time of day and lets you see the shading real time.

  3. Expert Member
    Michael Maines | | #3

    Hugh, one common approach when designing high performance homes is to plan windows and overhangs so the windows on the south side are fully shaded on the summer solstice, and fully unshaded on the winter solstice. You can try to do the same for west-facing windows but it's more challenging. With modern window coatings it's less important than it used to be, unless you're going for super high performance.

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