Sizing a Window and Awning for a Passive Solar Home
Purpose:
 To gain understanding of passive solar window design and seasonal solar elevation changes
 To practice engineering drawing techniques
Materials Required
 Graph paper
 A straight edge
 A protractor
 A ruler
 A pencil
Procedure
Imagine an existing 2-story house that
faces south and which has a window on the
first floor and none on the second. The
owner wishes to improve its passive solar features by adding a window to the second floor and an
awning above the window on the first.
To save expense, the owner wants to use the existing roof overhang on the second floor and
existing window on the first floor. You will produce an engineering drawing and use it to estimate
the size of the second-story window and the first-floor awning.

Draw a ½” boarder around the paper.

Draw a title box in the lower right hand corner. Fill in the title box information: drawing title,
your name, a drawing number and a revision number (this will be revision 0), the date, and a
space for the drawing to be approved.

On a separate piece of paper sketch what your drawing might look like and calculate the overall
dimensions of the part of the house you will draw. Use this to decide the scale. Choose the scale
so the drawing will fit on the paper and also so that it won’t be too small. It is good to take into
account the size of the boxes on the graph paper so that an even unit corresponds to 1 box. For
example, if the boxes are ¼” then a scale of 1”=4’ would work well because each box would
represent 1 foot.

Referring to your sketch, start drawing a house with the following dimensions:
o Height of first story: 9 feet
o Height of second story: 8 feet
o Roof slope: one unit up for every two units horizontally
o First story window is located 2 feet off the floor and is 2.5 feet high
o The roof overhang comes out 2 feet from the outside wall

Use a protractor to draw the angle of the sun rays for the winter and the summer.
o Put the origin of the protractor on a point of interest, like the top of the window, and
make sure it is horizontal.
o Draw a mark at the summer and winter elevation angles
o Remove the protractor and draw a line from that point on the wall to the summer and
winter marks. Make the lines distinctive, perhaps making one dashed and the other
solid, so one can tell summer from winter rays.
o Repeat for all points of interest and add a few other rays to make the rays look even
overall
o Although the highest summer elevation in North Carolina is about 78 degrees and the
lowest winter elevation is about 31 degrees, use a summer angle of 60 degrees to
exclude the sun from March through August. Keep the winter angle, but round it to 30
degrees for convenience.

Draw labels, arrows, and dimensions

Determine the size of the second-story window
o Find the topmost winter ray that reaches the side of the house. This is the top of the
window.
o Find the bottommost summer ray that reaches the side of the house. This is the bottom
of the window.
o Draw in the new window
o Use a ruler to measure the height on the drawing, then use the scale to calculate the
actual windows dimension and how high it is off the floor. Add the dimensions to the
drawing.

Determine the size of the first-story awning
o Find the highest winter ray that enters the window.
o Find the lowest summer ray that enters the window.
o Where these two rays meet it the tip of the awning. You can draw the awning from this
point to the house, taking any path to the house that you wish.
o Measure the horizontal length of the awning, use the scale to calculate the actual
length, and add the dimension to the drawing.
o Erase the parts of the rays that are now blocked by the awning
Analysis and Discussion
How might the sizing of the new window change if you could also change the roof overhang or
add a second awning?
In the space below, sketch the roof of a house with a skylight (essentially a window in the
roof). Sketch the summer sun and the winter sun along with the direction of their rays.
Describe how the passive solar gain for a skylight compares to that of a window. Does it work
the same way? Compared to a well designed window through a wall, will a skylight make the
house warmer or less warm in the winter? In the summer?
Imagine this same house at a lower latitude (closer to the equator). What happens to the
elevation angles in the summer and the winter?
How might this affect the size of an awning used to block the summer sun?
Rubric
Stellar
Well Done
OK
Missed the mark
Drawing
Drawing has all the
components specified,
is done neatly, and is
accurate
There are several
omissions or
inaccuracies and
neatness is marginal
Data Analysis
Window and awning
sizes are size logically
and the sizes
determined accurately
using the scale.
Discussion
Answers are in full
sentences, show
understanding of the
concepts.
Drawing has most of
the components
specified, is done
neatly, and is mostly
accurate
Window and awning
sizes are
approximately correct
and the sizes
determined accurately
using the scale.
Answers show
understanding of the
concepts, but are
either brief or
imprecise.
Serious omission of
drawing components,
drawing does not
reflect the house,
sloppy drawing
Both the graphical
analysis to determine
the sizes and the
conversion to real
dimensions are
inaccurate.
Answers are missing or
so short as to provide
no insight into the
understanding by the
student.
Window and awning
sizes wrong but the
sizes determined using
the scale match what
is on the drawing.
Very brief answers
demonstrating little
insight.