HOW TO USE THE OVERHANG DESIGN SHADING CALCULATOR

The general question addressed by overhang design is: to what extent is a window shaded by a horizontal overhang at certain hours of the day on certain days of the year? 

With this information, an architect, designer, builder, or home owner can design a window system that admits sunlight when it is desirable, and provides shade when it is not.

The interface to overhang design consists of a window graphic on the left, and inputs on the right.

You should first set the latitude and window orientation inputs (the orientation is the compass direction that the window faces). You should then enter information about the dimensions of your window, then try different overhang sizes and positions at different times on different dates.

As you enter various combinations of inputs, the window graphic will change to reflect the extent to which the window is shaded by the overhang. The black bar above the window represents the overhang, and the light gray quadrilateral that extends from its lower side is the overhang shadow. If the overhang is not presently shading the window (for instance if the sun is below the horizon), there is a note on the screen to that effect.

Units
For maximum flexibility, the tool supports any linear unit of measurement you wish to use - millimetres, centimentres, metres, etc. Just be sure to use the same units for all measurements, and scale all units so that they range from 0 to 10.

For example, if your window dimensions are 2400mm x 1200mm, scale them down by a factor of 10 to 2.4 x 1.2, and use those for your inputs. Scale overhang dimensions by the same factor.

Inputs
To change input values, just click and hold down the round "knob" of the slider or dial, and move it to the appropriate value, then let go. Note that you shouldn't worry too much about precision here, since an inch or two, or a minute or two, makes little difference.

Location
Set your location using the latitude compass. Latitude varies from 0 to 90 degrees North, and from 0 to 90 degrees South.

Window orientation
Use the "Window Faces" compass to indicate the direction that your window faces (i.e., the compass orientation of the wall on which the window is installed).

Please note that this program uses true (solar, or geographic) orientations, not magnetic orientations, so South on the compass input is true South, not magnetic South. You can translate compass orientations into true orientations by compensating for magnetic declination.

Window dimensions
The two parametres you define about your window are its height and width.

The height and width are the size of the aperture of the glass (not the frame), and are measured in whatever units you'd like (millimetres, centimetres metres, etc. - just be sure to be consistent throughout the inputs).

Overhang
The overhang width is its horizontal dimension (be sure to use the same units you used to describe the height and width of the window).

The overhang depth is how far it protrudes from the wall.

The height above the window is the distance from the top of the window aperture (the glass, not the entire frame assembly) to the bottom of the overhang.

The horizontal offset is how far the horizontal center of the overhang is offset from the horizontal center of the window.

Note that for pitched overhangs, you should use the lowest edge to determine the Height Above Window value, as shown here:

If a pitched overhang extends under the top of the window, set the Height Above Window value to zero, and reduce the Window Height value as indicated here, since the upper portion of the window will always be shaded (unless the sun sneaks in around the side of the overhang):

Date/time
To set the date, move the month and date sliders to the appropriate values.

To use the clock, click and drag the thumb around the perimetre of the clock dial. By default, the clock is in 12-hour mode, which provides access to times between 6:00am and 6:00pm.

If you click the "12-hr" text in the lower right corner of the screen, you can turn on 24-hour mode, and the clock will allow you to select values from 0000 to 2400 (12:00 noon is still at the top of the dial).

The time used in this program is local solar time, not clock time, so there are no corrections for time zone, daylight savings time, etc. With local solar time, the sun is always due South (or North) at noon.

An important note about overhangs in temperate climates
If you're using this tool to optimise an overhang to provide shade at certain times of year and admit sun at others, please keep in mind that in most temperate climates the hottest time of year is one to two months after the summer solstice, and the coldest time of year is one to two months after the winter solstice. This is due to the significant thermal inertia of the surface of the Earth.

This phenomenon means that it's not enough to provide shade on the summer solstice and admit sun on the winter solstice. It's important to review local climate data in order to determine which months are the most critical for heating and cooling, and optimise an overhang to provide and avoid shade at those times.

This isn't easy, of course, since the inertial lag means that the sun will follow the same path in the sky a couple months before and after each solstice, and you'll probably want shade at one of those times but sun at the other. Your climate and building design may warrant a bias toward more or less shade, or you may consider movable shading devices, preferably external to the window. Please consult an experienced design professional for details.