Perlin*, co-author [with Ken Butti] of A Golden Thread -
2500 Years of Solar Architecture and Technology, provides
here a short summary of the evolution of passive solar design
- Passive Solar refers to an approach to heating and
cooling homes through simple devices and architectural design,
as opposed to mechanically operated heating and cooling systems.
ancient Greeks planned whole cities in Greece and Asia Minor
such as Priene, shown in the illustration, to allow every homeowner
access to sunlight during winter to warm their homes. By running
the streets in a checkerboard pattern running east-west and
north-south pattern every home could face south, permitting
the winter sun to flow into the house throughout the day.
the fifth century BC., the Greeks faced severe fuel shortages. Fortunately,
an alternative source of energy was available - the sun. Archaeological
evidence shows that a standard house plan evolved during the fifth
century so that every house, whether rural or urban, could make
maximum use of the sun's warm rays during winter. Those living in
ancient Greece confirm what archaeologists have found. Aristotle
noted, builders made sure to shelter the north side of the house
to keep out the cold winter winds. And Socrates, who lived in a
solar-heated house, observed, "In houses that look toward the
south, the sun penetrates the portico in winter" which keeps
the house heated in winter. The great playwright Aeschylus went
so far as to assert that only primitives and barbarians "lacked
knowledge of houses turned to face the winter sun, dwelling beneath
the ground like swarming ants in sunless caves."
section of a Roman heliocaminus. The term means "sun furnace."
The Romans used the term to describe their south-facing rooms.
They became much hotter in winter than similarly oriented Greek
homes because the Romans covered their window spaces with mica
or glass while the Greeks did not. Clear materials like mica
or glass act as solar heat traps: they readily admit sunlight
into a room but hold in the heat that accumulates inside. So
the temperature inside a glazed window would rise well above
what was possible in a Greek solar oriented home, making the
heliocaminus truly a "sun furnace" when compared to
its Greek counterpart.
in ancient Rome was even more profligate than in Classical Greece.
In architecture, the Romans remedied the problem in the same fashion
as did the Greeks. Vitruvius, the preeminent Roman architectural
writer of the 1st century BC., advised builders in the Italian peninsula,
"Buildings should be thoroughly shut in rather than exposed
toward the north, and the main portion should face the warmer south
side." Varro, a contemporary of Vitruvius, verified that most
houses of at least the Roman upper class followed Vitruvius' advice,
stating, "What men of our day aim at is to have their winter
rooms face the falling sun [southwest]." The Romans improved
on Greek solar architecture by covering south-facing windows with
clear materials such as mica or glass. They also passed sun-right
laws that forbade other builders from blocking a solar-designed
structure's access to the winter sun.
the ancient Romans, the 18th century Dutch and others in Europe
at the time, used glass-covered south-facing greenhouses to
capture solar heat in wintertime to keep their exotic plants
warm. To prevent the solar heat captured during the day from
escaping, the Dutch covered the glass at night with canvas coverings.
Romans not only used window coverings to hold in solar heat for
their homes but also relied on such solar heat traps for horticulture
so that plants would mature quicker, produce fruits and vegetables
out of season, and allow for the cultivation at home of exotic plants
from hotter climates. With the fall of the Roman Empire, so to came
the collapse of glass for either buildings or greenhouses. Only
with the revival of trade during the 16th century came renewed interest
in growing in solar-heated greenhouses exotics brought back from
the newly-discovered lands of the East Indies and the Americas.
Trade also created expendable incomes that allowed the freedom to
take up such genteel pursuits as horticulture once more.
architects such as Humphrey Repton brought the sunlit ambiance of
the greenhouse right into the home by attaching it onto the south
side of a living room or library. On sunny winter days the doors
separating the greenhouse and the house were opened to allow the
moist, sun-warmed air to freely circulate in the otherwise gloomy,
chilly rooms. At night, the doors were shut to keep in as much solar
heat as possible. By the late 1800s the country gentry had become
so enamored of attached greenhouses that they became an important
architectural fixture of rural estates.
19th-century solar remodel: Architect Humphrey Repton turned
a dull interior (left view) into a vibrant home by opening up
the house to a south-facing greenhouse.
AMERICAN SOLAR HERITAGE
solar architecture began with its indigenous heritage. Acoma,
built by the Pueblo Indians in the 12th century AD and continuously
inhabited since then., serves as an excellent example of their
sensitivity to building with the climate in mind. The "Sky
City," built atop a plateau, consists of three long rows
of dwelling units running east to west. Each dwelling unit has
two or three tiers stacked one behind the other as to allow each
one full exposure to the winter sun. Most doors and windows open
to the south to catch the warm solar rays of winter. The walls
are built of adobe. The sun strikes these heat-absorbing south
wall more directly in winter than during summer time. The sun's
heat travels through the adobe slow enough to reach the interior
as night falls, heating the house through the night. Insulating
the ceiling with straw keeps the horizontal roof, vulnerable to
the rays of the high summer sun, from allowing too much heat to
enter the house.
Aerial view of the tiered rows of houses at Acoma
Spaniards who settled in the American southwest often built to take
advantage of the winter sun : they aligned their homes east to west
so the main portion of the house faced south. Shutters outside the
windows were closed at night to help keep from escaping the solar
heat that had flowed in all day during wintertime.
early California family posing in front of the their Spanish-Colonial
Settlers in New England considered the climate when they built their
homes. They often chose "saltbox" houses that faced toward
the winter sun and away from the cold winds of winter. These structures
had two south-facing windowed stories in front where most of the rooms
were placed and only one story at the rear of the building. The long
roof sloped steeply down from the high front to the lower back side,
providing protection from the winter winds. Many saltbox houses had
a lattice overhang protruding from the south facade above the doors
and windows. Deciduous vines growing over the overhang afford shade
in summer but dropped their leaves in winter, allowing sunlight to
pass through and penetrate the house.
colonial "salt box" house, typical of New England
architecture of the 18th century.
The Royal Institute of British Architects developed in the early
1930s the device shown in this photograph called the heliodon
to help architects determine the effects of the sun on buildings
before they went up. By mounting a model of a proposed structure
on a rotating drawing board below a fixed light source simulating
the sun, designers could easily ascertain the solar exposure
of the proposed building.
the terrible slums that blighted European cities during the industrial
revolution sparked a renewed interest in building with the sun.
As one English city planner bent on housing reform urged in the
first decade of the twentieth century, "Every house should
have its face turned to the sun, whence comes light, sweetness
and health." Young architects on the Continent agreed, declaring
that their profession should embrace functionalism over aesthetics.
Functionality meant to many designing houses that satisfied the
basic needs of those living in them. In the relatively chilly
European climate this dictum meant providing dwellers with a warm
haven. Therefore an architect wishing to build a useful house,
Hannes Meyer, the leader of functional architecture in Germany,
argued, must consider its body "to be a storage cell for
the heat of the sun." Hence, "Maximal use of the sun,"
as far as Meyer was concerned, was "the best plan for construction."
Meyer, who became the director of the highly famous and influential
Bauhaus architectural school, told fellow architects that to achieve
optimum sunshine in buildings, they must conduct or at least be
privy to scientific research into the sun's year round movement
relative to the Earth. Germany led a renaissance in solar building
during the 1930s that spread throughout Europe only to be stamped
out by the Nazis and then World War II.
for a prefabricated solar-oriented homeThe Nazis condemned functional
architecture as Jewish and when they came to power, a good number
of German architects designing solar buildings fled, many ending
up in America. George Fred Keck, a Chicago architect, befriended
some of these expatriates and through their influence began
designing homes in the Chicago area according solar building
principles - expansive south facing glass to trap the winter
sun, long overhangs to shade the house in summer, minimal east-west
exposure to prevent overheating in summer and fall, and the
placement of secondary rooms, garages, and storage corridors
on the north side to help insulate the living quarters from
the cold north winds. Keck had a knack for publicity and called
the houses he designed "solar homes." By the mid-forties
Keck's work caught the attention of the national media. House
Beautiful, Reader's Digest and Ladies Home Journal featured
his work. Fuel rationing during the war inclined the American
public toward valuing the energy saving features of solar homes.
When war ended, the building market exploded. With the wartime-conservation
ethic still imbued in most people's minds, many manufacturers
in the prefabricated home industry adopted solar design features
for leverage in this highly competitive market.
TUNING SOLAR HOMES
Studies of houses
with large amounts of glass on the south side demonstrated that
they experience much greater temperature swings than ordinary homes,
warming quickly during the day due to accumulating the sun's heat
and cooling off rapidly at night due to large heat losses through
the windows. Tucson Architect Arthur Brown did away with the unwanted
fluctuations in temperature by running a thick black wall between
the sun porch next to the south facing glass and the living quarters.
During sunny winter days, sunlight struck the black wall and the
concrete absorbed the solar heat. Estimating that heat moves through
the wall at one inch an hour, Brown made the wall eight inches thick.
As evening approached, the solar heat soaked up by the wall began
to radiate into the rooms and continue to do so into the night.
By morning all the solar heat in the wall had dissipated into the
living areas, leaving the wall totally cooled down and ready for
another heating cycle.
view on a sunny winter day of the Tucson solar home designed
by architect Arthur Brown. Sunlight streaming through the large
expanse of south-facing window glass warms the masonry walls
inside which pass the heat on to the living quarters after sundown.
HEATING FOR THE PUBLIC
architect Arthur Brown, responsible for the solar-absorbing wall
described previously, also designed in 1948 the world's first solar-heated
public building. Since students attended class between 9 AM and
3 PM, Brown did not have to worry about storing solar energy since
no one needed heat at night or in the very early morning. To keep
costs down, he used the roofing supports to separate the space between
the ceiling and the roof into channels. In this way, the roof itself
served as the solar collector. The school's fan that had forced
gas heated air through the building, now pushed air through the
channels. The sun's energy heated the air and a second fan distributed
that heat into the classrooms when needed. The solar system provided
the school with 86% of its heat. But in 1958, with energy cheap
and the school district decided to expand the campus, the authorities
chose a gas-fired furnace instead. Cheap energy running highly reliable
and easy to use heating and cooling systems led to an almost universal
disinterest in solar design.
solar-heated Rose Elementary School in Tucson Arizona. It obtained
over 80% of its heat from solar energy for an entire decade,
beginning in 1948.
70'S AND BEYOND
in ancient Greece, rising fuel costs in the 1970s forced many to
turn to the sun again for help. The Village Homes subdivision's
layout uncannily compares to the planning of solar cities in ancient
Greece and Asia Minor. But as fuel prices dropped in the mid-1980s,
people once more turned their backs from the sun. With electric
and fuel prices again on the rise, history offers many lessons that
can help smooth our transition to an enduring Solar Age.
Aerial view of the Village Homes subdivision built in the late
1970s in Davis, California. The layout of the subdivision allowed
every house to face the winter sun.
Perlin lives in Santa Barbara, California and can be contacted at