Weather depends ultimately on the sun, as Washington’s record-setting temperatures this summer remind us. Yet buildings in our climate zone, including individual homes, are rarely designed to respond directly and naturally to the sun. Year-round indoor comfort depends mostly on machines, not inherent architectural geometry or architecturally induced natural effects.
Conversely, summertime outdoor comfort depends primarily on natural effects, not machines. Cooling breezes, shade created by architecture and trees, and evaporation from pools, streams, rivers or lakes help keep us comfortable outdoors. Indeed, Washington is more fortunate than many cities during hot weather thanks to the city’s extensive tree canopy shading its streets, avenues, parks and back yards.
Environmental scientists and engineers characterize sun-drenched cities as “heat islands,” a metaphoric reminder that outdoor temperatures experienced within such cities are palpably higher than in surrounding suburbs and exurbs.
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Outside in Washington on a summer day, you feel hot because naturally high air temperatures are further elevated by thousands of air conditioning systems pumping heat from inside buildings into the atmosphere. And direct solar radiation makes you feel even hotter, as does radiation from concrete, masonry and metal surfaces heated by the sun.
My hometown of Houston is nation’s fourth-largest city and one of its biggest heat islands. Yet the sun had little influence on the planning of this flat, sprawling metropolis whose climate is oppressively hot and humid for half the year. Indeed, without air conditioning, Houston would have remained a small Gulf Coast city.
Houstonians escape the city’s chronically brutal climate by staying indoors. In fact, people working, living or visiting downtown never need to go outside. A network of underground pedestrian tunnels crisscrosses downtown Houston, connecting block after block of soaring skyscrapers and parking garages. Streets often seem deserted as the air-conditioned tunnels siphon off almost all pedestrians and streetscape activity.
Since the mid-20th century, technology and relatively inexpensive energy have allowed us to design urban environments and architecture that operate independently of the sun.
Modern-era buildings in Washington are heated, cooled, ventilated and illuminated by increasingly sophisticated mechanical and electrical systems. Thanks to high-tech window glass and curtain walls coupled with high-resistance thermal insulation, today’s dimensionally thin building skins are indeed skin-like. They enable us to ignore the sun while reducing energy usage and expense for tempering and lighting interior space.
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Yet there are still economic and even aesthetic costs when we design architectural form that disregards where the sun is and what its positive and negative effects are.
With efficient HVAC and electrical systems, plus well-insulated roofs and walls, sun-sensitive building geometry is deemed unnecessary. Windows in facades facing north, south, east and west can be the same, even though the sun’s impact on each facade differs.
This typifies not only office and apartment buildings, but also most single-family houses. Siting standardized model homes on subdivision lots, regardless of lot orientat ion, is constrained only by the need for front-entry facades to face streets. Sun-based design of roofs and roof overhangs, facades and fenestration occurs infrequently.
Shutters to block the sun were invented centuries ago to keep rooms cool and provide privacy. During many days of the year, being able to open and close exterior shutters on windows facing south, east and west is an effective means for warm-weather solar control. Yet almost all shutters flanking residential windows are cosmetic and non-functional.
Regulations governing yard dimensions and building setbacks on individual parcels and lots usually disregard solar orientation, although sun and shade conditions greatly affect the microclimate, gardening possibilities and comfort of outdoor spaces next to buildings.
To reduce reliance on machines for achieving comfort, architecture should both take advantage of the sun and mitigate its adverse impact. Solar orientation, along with other factors, should influence overall building design and orientation.
Facades as a whole, window designs and habitable spaces — porches, balconies, decks and terraces — that are part of and extend facade compositions should capture desirable winter sun while blocking out or filtering unwanted summer sun.
Dimensionally adequate roof overhangs can shade exterior walls exposed to the sun to reduce air conditioning loads. Deciduous shade trees on the southeast, south and southwest sides of a house or low-rise building are especially effective in providing warm-weather solar control.
For many days of the year when weather is favorable, natural ventilation and, ideally, cross-ventilation are desirable and cost-effective. Accordingly, windows, doors, skylights or wall panels should be partly or fully operable.
In recent years, rooftop solar collectors converting solar energy to electricity have become practicable and cost-effective. Solar collectors do double duty: They create usable, renewable energy that reduces electric bills. And they intercept solar radiation that otherwise would heat roofing materials and building interiors.
The bottom line: We are harvesting solar photons more than ever, but there is still much room for improvement in how we shape our built environment in response to the sun.
Roger K. Lewis is a practicing architect, a professor emeritus of architecture at the University of Maryland and a regular guest commentator on “The Kojo Nnamdi Show” on WAMU-FM (88.5).