An overhang as long
as possible should be used
on east and west windows.
Too often, however, an
Barn doors are used on the west windows to block the very hot summer afternoon sun. They
are left open all winter, on cloudy days and until 1 p.m. in the summer.
additional shading system
will be required.
East, West Windows
May Need Added Systems
Because an effective overhang on east and
west windows has to be more than 100 feet
( 30. 5 meters) long, it is obviously not ideal,
and for that reason, many books recommend
vertical fins for east and west windows. That
recommendation turns out to be a fallacy. Not
only do vertical fins shade less than their horizontal equivalent, called louvers, but fins also
reflect light to the right and left instead of to
the ceiling for the best daylighting. However,
fins do work on north windows, because the
summer sun shines into north windows from
northeast and northwest at rather low-altitude
angles (see again the Burton Barr Central
Library photos).
Thus, in temperate climates, vertical fins
work well on north windows and horizontal
overhangs work well on south windows, but
what is best for east and west windows? To
maximize the view, an overhang as long as
possible should be used on east and west
windows. For that reason, porches, carports,
garages and large awnings belong on the
east and west sides of low-rise buildings.
The length of the overhang on the east and
west will determine how long before and
after noon the windows will be shaded.
Unfortunately, in most cases the sun will
usually shine under overhangs in early morning and late afternoon when shading is still
needed. With luck, trees and neighboring
buildings will shade the lower-floor windows. If the existing shade for the low sun
Copyright © 2012 by the American Solar Energy Society Inc. All rights reserved.
Figure 5. It is a common but serious mistake to
have an overhang the same width as the window,
because it will be seriously outflanked by the sun
most of the time. If the window faces south, it will
be fully shaded only at noon.
Read On
For more information on shading, see
the author’s book, Heating, Cooling,
Lighting: Sustainable Design Methods
for Architects, 3rd edition, ©2009, John
Wiley & Sons.
For more information on passive
solar heating, see both the above
book and The Passive Solar Design and
Construction Handbook, by Steven
Winter Associates and Michael J.
Crosbie, ©1997, John Wiley & Sons.
— N.L.
is insufficient, then adding a vertical trellis
with plants can be effective. For high-rise
residential buildings, use east and west bal-conies with large and many potted plants. In
multi-story or high-rise commercial buildings, the best solution for east and west
windows may be the use of exterior venetian
blinds, which are popular in some parts of
Europe (see photo, page 26). Unfortunately,
interior venetian blinds are much less effective; exterior shading systems are about four
times better than indoor shading in keeping
out solar heat.
My home in the Colorado mountains
is a passive solar house with lots of south
and very few north windows. Because of the
beautiful views to both the east and the west,
large windows also face those directions.
To shade these difficult orientations, I use
a pleated awning (toldo) to shade both the
east window and deck (see photos, top of
page 28). Because the 10-foot (3-meter)
awning and a large tree to the east shade
much of the morning sun, we use indoor
shading for the short time that the low sun
does shine into the east windows. The west
windows are shaded by barn doors that I use
only on hot, sunny summer afternoons (see
photos, top of page). Barn doors and their
hardware are quite inexpensive.
Shading, more than any other solar strategy, requires a good understanding of solar
geometry. To better understand solar-responsive design strategies, check out my article on
solar geometry in the May issue. ST
