Page E1.2 . 25 August 2004                     
ArchitectureWeek - Environment Department
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On Not Cooking Clients


The dangers of heat are enhanced by air pollution, such as ground-level ozone, which tends to rise along with the temperature. An even more important interaction occurs between heat and humidity. When the humidity is high, one experiences the temperature as higher than it really is. For instance, 88 degrees Fahrenheit (31 degrees Centigrade) at 85 percent relative humidity feels like 102 degrees F. (39 degrees C.) at 40 percent humidity.

Medical stress from heat rises with the heat index, the perceived temperature when heat and humidity are combined. At a heat index of 80-90 F. (27-32 C.), we may experience fatigue, which can lead to more severe complications. At 90-105 F. (32-41 C.), heat cramps appear, and heat exhaustion becomes possible, characterized by thirst, headache, and nausea. Heatstroke is possible at a heat index of 105 F. (41 C.) and highly likely at 130 F.(54 C.) . Then the body's regulation system fails, body temperature keeps rising, and death can occur.

This entire process can take place without the overheated person being driven to seek cooling. The stealthy nature of heat-related illness is most insidious overnight. The ill effects of heat accumulate, so if the body has not recovered from yesterday's daytime heat, today's is more dangerous.

The elderly have a reduced ability to adjust to heat because they sweat less and dehydrate easily. The obese and those who do not exercise regularly are also at higher risk. Some medications, as well as alcohol and cocaine, increase vulnerability to heat.

The body always responds to heat. The familiar skin flushing that we experience fosters the loss of excess body heat. Though each of us is born with about the same number of sweat glands, exposure to heat in our early lives affects how many sweat glands are "activated." So people raised in hot climates are generally better able to tolerate high temperatures.

How Our Cities Bake Us

In practical terms, the strongest risk factor for heatstroke in the United States is poverty, which forces people to live in housing that is not air-conditioned, in neighborhoods where crime discourages outdoor time and open windows, and where shade trees may be sparse.

Quite a few city features contribute to heat accumulation. Dark-colored building surfaces like black roofs become much hotter than lighter, more reflective ones. Other urban features impede the dissipation of heat and humidity, such as building surfaces that are not separated from one another by heat-releasing materials.

Common urban building surfaces, such as brick and concrete, store heat and transmit it to building interiors. Unless energy is spent to get rid of the heat, nighttime temperatures indoors can exceed those outdoors. In massive urban buildings, if an apartment is hot at sunset, it may still be warm at sunrise. Apartments on top floors are most affected.

The lack of foliage in the city means a lost opportunity for plants to provide shade and natural cooling (through evaporation of water from soil and leaves). City buildings also contribute to the "urban heat island" effect by blocking cooling winds.

Although U.S. building codes protect people from excessively cold weather, there are no similar guidelines to protect city dwellers from heat. Facing such a void in safety regulation, architects and urban planners should take it upon themselves to consider heat mitigation in neighborhood and regional planning.

Solutions to Urban Overheating

An obvious response would be to require universal air conditioning, but that simple answer to this complex problem does not stand up to scrutiny. Mechanical air conditioning is expensive and inefficient. It actually concentrates and dispels heat into the environment, where it is absorbed into structures that accumulate and radiate it. While it can make some interiors cooler, air conditioning makes the city hotter.

Contemporary architects may take cues from traditional designers, who have embraced nonmechanical means of cooling for millennia. Baruch Givoni, in Climate Considerations in Building and Urban Design, provides many examples that use shading, surface treatments, window orientation, and heat capturing materials to reduce the extent to which dwellings heat up.

Traditional buildings use stilts, heat-drawing chimneys, and spatial planning to increase ventilation and heat dissipation. In addition, reflective surface materials can reduce a building's absorption of light, which turns to heat. Green spaces around and atop buildings can enhance heat dissipation.

Additional means could be explored to temporarily shade the tops of buildings on hot sunny days. Older, proven ventilation systems such as operable transoms above doorways (to move hot air up and out) might be paired with windows that open (or vents below windows) to promote air movement.

Architectural Response to Emergency

I believe architects should consider themselves to be public health professionals because they can provide the needed leadership for these changes to occur. To provide a framework for thinking about how architects meet human needs, I have turned to the field of psychology, which describes, for its field, a "hierarchy of needs." This hierarchy can be adapted to physical needs.

"Survival needs" include air, water, and thermal environment that ensure we do not die right away, say in minutes to hours. "Basic needs" include clean food, basic education and employment, and safety from assault, to ensure that we survive for years and do not suffer greatly.

"Prospering needs" extend to finer luxuries such as higher education, the arts, and creature comforts beyond the basics. We also think of this category as the "pursuit of happiness." It is the last category to which architects commonly aspire for housing their clients. For some city dwellers, however, even more basic needs are not being met.

These three categories of need can help describe how well human needs are being met by the built environment. Let's encourage architects to evaluate the success of projects by how well they address the full spectrum of these needs. These categories suggest the framework for a "human needs impact statement" related to plans for a building, a neighborhood, or a city.

Discuss this article in the Architecture Forum...

Katherine Kaufer Christoffel, MD, MPH is a physician, professor of pediatrics and preventive medicine at the Feinberg School of Medicine at Northwestern University, and director of the Center for Obesity Prevention and Management at the Children's Memorial Research Center in Chicago.

The drawings for this article are from Climate Considerations in Building and Urban Design by Baruch Givoni, © 1998 John Wiley & Sons, Inc. This material is used by permission of the publisher.



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Facade treatments to reduce glare can alleviate some overheating without air conditioning.
Image: Baruch Givoni

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Triangular "bay" windows in eastern and western walls, facing southeast and southwest, respectively, maximize solar gain in winter and minimize solar overheating in summer.
Image: Baruch Givoni

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Cooled soil under a building serves as a heat sink. Embedded air pipes serve as heat exchangers to transfer interior heat to the cooled soil.
Image: Baruch Givoni

ArchWeek Image

A breezeway cutting across a house.
Image: Baruch Givoni

ArchWeek Image

Le Corbusier's scheme of a double-loaded apartment building. Each unit has two external walls, enabling cross ventilation.
Image: Baruch Givoni

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A comparison of the ventilation potential (optional locations for windows) of two design solutions: one compact and one spread out, with the same floor area and program.
Image: Baruch Givoni

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A flat roof with direct solar heating in winter by a roof monitor and passive cooling in summer by a roof pond with floating insulation.
Image: Baruch Givoni


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