be the answer, but we have as yet no sure guidelines for designing and building such structures.

Sick Building Syndrome

Historically, buildings have been quite leaky of air and have more or less ventilated themselves. In recent years, largely in response to calls for increased energy efficiency, we have tended to construct buildings that are virtually airtight. Unless mechanical ventilation is provided in these buildings, moisture levels in the interior air can rise to levels such that various molds and mildews will grow on surfaces and in ductwork. We have begun to use more and more synthetic materials in buildings, some of which emit gases such as formaldehyde. An airtight building can also create problems with fuel-burning appliances that can't get enough air for clean combustion, causing them to give off carbon dioxide and carbon monoxide to the interior air. From problems such as these has arisen the recent phenomenon of sick building syndrome, a catch-all term that refers to buildings whose interior air quality is so bad that it makes many of the occupants ill.

Because of its many possible sources, the causes of sick building syndrome in a specific building are often difficult to diagnose. In most cases, a cause can be found, and remedial action can be taken. Sometimes merely cleaning the air-conditioning ductwork will cure the problem. It may be necessary to provide equipment to lower the humidity of the interior air. Moldy or mildewed materials may have to be removed and replaced. Combustion air inlets for furnaces sometimes help by reducing the likelihood that noxious combustion products such as sulfur dioxide and carbon monoxide will be generated by the fire. In the meantime, buildings often must be evacuated until the problem is solved.

Vinyl wall coverings in the interiors of buildings in hot, humid climates have often been problematic. These sheet materials are often impervious to water vapor and air, but when it is hot outdoors and cool indoors, they are on the cool side of the vapor retarder, which is the wrong side. Moisture accumulates on the back side of the wall covering, where it creates ideal conditions for the growth of molds and mildew. Manufacturers of the material have responded by developing pervious versions and by treating the material with long-lasting fungicides at the time of manufacture.

Routine Building Maintenance

Routine building maintenance includes many sorts of repair, renewal, and cleaning operations. On the exterior of a building, impervious wall surfaces such as glazed tile, porcelain enamel on steel, glass, aluminum, and stainless steel have extremely long lifetimes under normal circumstances and need no maintenance other than periodic washing and occasional replacement of the mortar or sealant between units. Exterior paints, stains, and varnishes deteriorate quickly in sunlight and rain and must be renewed every few years. With white paint this rapid degradation has some advantage, because the progressive chalking and washing away of the surface of the paint film keep the coating clean and bright in appearance.

The droppings of pigeons, starlings, sparrows, gulls, and other birds contribute to exterior maintenance problems on some buildings. Eliminating snug crannies from the exteriors of buildings deals with much of the difficulty. Devices that produce unpleasant sounds or electric shocks, or that have rows of spikes to prevent roosting, may be needed in extreme cases.

Window glass quickly accumulates layers of dirt on both sides. In time these will obscure vision and block daylight. Periodic washing is made easier by using window types that allow both sides of the glass to be reached from inside the building. Otherwise, ladders are necessary to reach the windows of low buildings, and movable suspended staging is needed for taller buildings. One glass manufacturer markets a glass with a transparent catalytic coating on the exterior that works with sunlight to convert most dirt to soluble compounds that wash away in the rain. The additional cost of this glass is often justifiable because of the reduction in glass maintenance expense over the life of the building.

Windows must be designed to make occasional replacement of broken panes easy, preferably working from inside the building. Most glazing compounds (the gummy substances in which glass is bedded) harden with age and eventually crack and fall away, needing replacement. Window frames need periodic inspection for corrosion, decay, leakage of air or water, excessive tightness or looseness of operation, and wear or breakage of hardware.

Interior surfaces of buildings are generally safe from the destructive effects of sun, rain, and wind, but they are exposed instead to the wear, tear, and soil of human occupancy. Walls and ceilings collect dust and dirt from the air and from the hands, heads, feet, and furniture placed against them. In areas such as kitchens and bathrooms where walls are especially exposed to soiling, gloss or semi-gloss enamel paints make them easier to wash. Smooth wainscots of glazed ceramic tile or plastic laminate are advisable in wet locations (21.4). Doors, windows, and their wooden casings are usually coated with gloss or semi-gloss finishes to make finger marks easy to remove. When interiors are repainted, the first step is to fill any plaster cracks. Serious plaster cracking is often indicative of structural problems or water leakage, however, and should not be smoothed over before a diagnosis can be made and corrective action taken. When choosing

colors of paint, wallpaper, or wood paneling, we should consider what effect the new color will have on lighting levels in the room. Only white and the very lightest tints are highly reflective of light. Other colors absorb much or most of the light that strikes them and may create an effect that is both excessively somber and intolerably dark.

Floors, which undergo the abrasions of grit trodden underfoot, are the most subject to wear of any interior building surfaces. They also are a source of dust that is kicked up by passing feet and deposited on walls and furnishings. Floor maintenance is therefore the largest single component of day-to-day building care. We can keep out much foot-borne dirt by providing a doormat or grille at the entrance door. Vacuuming, dusting, sweeping, and scrubbing remove dirt before it piles up too deeply. Waxing some types of floor surfaces offers some protection against wear and makes washing or dusting the floor considerably easier. Floors of hard stone or hard tile are highly resistant to abrasion and are easily washed. Soft stone, soft tile, and wood floors are abraded much more quickly. In most cases, wood floors can be sanded and revarnished after severe abrasion. Soft tiles and stones occasionally need replacement. On public stairways, where wear is exceptionally severe and eroded stairs present a particular safety problem, hard materials should be used. Stair treads are available with nonslip surfaces made of extremely hard abrasives.

The maintenance of floors, countertops, and wainscots is easier, and their appearance generally improved, if their surface is mottled, streaked, or patterned. Such textures camouflage small splotches and streaks of dirt, making them much less noticeable than they would be on a plain-colored surface. Plain-colored surfacing materials frequently cost more than otherwise identical mottled ones, because even the tiniest manufacturing defect will be cause for rejecting a plain-colored product, whereas it might not be noticed in a mottled one.

Graffiti can be a large problem in public places. The would-be artist usually is discouraged if faced with a surface so rough, irregular, or richly patterned that any superimposed message is likely to be illegible, if it is possible to apply it in the first place. An exceptionally smooth, easily cleaned or easily repapered surface, on the other hand, encourages the addition of ad hoc names, notes, and pictures. As long as the accumulating pattern is pleasing, it can be retained. Obscenity or excessive messiness can be obliterated, and the process can begin anew. Graffiti-resistant surface coatings that repel most types of paints and markers are effective on some types of surfaces.

Except for its mechanical systems, a building has few moving parts that need care. Drawers, doors, and windows require occasional adjustment and lubrication. Hinges, latches, and locks are especially prone to wear and breakage. Doors that accommodate large numbers of people, in markets, schools, and other public buildings, require more frequent maintenance and occasional replacement of worn working parts. Ball-bearing hinges greatly reduce wear and can be helpful in reducing maintenance costs for swinging doors in heavily used buildings.

All the mechanical systems in a building require systematic programs of maintenance. The air filters of heating, ventilating, and cooling equipment must be cleaned or replaced at regular intervals. Burners need at least annual cleaning and adjustment for maximum efficiency of combustion. Motors, fans, pumps, and compressors require lubrication and replacement of rubber belts.

Plumbing fixtures must be cleaned regularly and their drains kept free of obstructions. Faucets and toilet valves need constant repair. Water supply piping may in time fill with mineral scale and have to be replaced. Waste piping is prone to clog now and then with hair, paper, cooking fats, or invading tree roots. Devices ranging from a length of stiff wire to elaborate rotary knives on the end of a long cable can be introduced at cleanout ports in the piping to clear the obstacles. Water heaters are especially susceptible to scaling from mineral-laden water, and their electrical or fuel-burning components need periodic attention.

Incandescent bulbs, fluorescent tubes, and fluorescent ballasts are the items in a building's electrical system requiring the most frequent replacement. Regular cleaning of fixtures and occasional cleaning and painting of ceilings and walls to renew their reflectivity of light are also required for maximum performance of the electrical lighting system. Light switches and electrical appliances wear out relatively quickly. The other components of the electrical system do not usually wear out, but electrical systems as a whole become obsolete fairly rapidly. Older systems are universally too small in capacity, do not furnish enough outlets, and do not meet today's standards of grounding and shock protection. Future developments are certain to eclipse today's most up-to-date wiring installations in a few years. Fortunately, new wiring is fairly easily installed in existing structures, especially where plenty of capacity is available in conduits, which are metal or plastic tubes within which wiring is run.

Elevators and escalators are generally serviced at frequent intervals by specialists associated with the manufacturers of the devices, and they are inspected regularly for safety by representatives of the local municipality. Elevators in particular are extremely complex and diverse in their mechanisms and controls and are subjected to heavy wear. Because elevators also present a unique potential for human disaster, their mechanisms are designed with very large factors of safety; numerous safety devices are incorporated into their design; and maintenance must be frequent and thorough.

Designing for Growth and Change

Among the more subtle skills of an experienced designer is the art of using the natural forces of deterioration to improve the building over time. There are few things more satisfying than seeing a building grow more attractive with age, rather than shabbier. To construct such a building, we must first recognize that the surfaces of the building are both the visible face of the building and the surfaces that must withstand the abuse of sun, rain, wind, soot, dirt, and human wear. Any material that grows steadily worse in appearance when exposed to these forces should be avoided. A new car furnishes numerous examples of such materials: When it emerges from the showroom, it gleams seductively with bright, flawless enamel, polished chromium, and sparkling curves of glass. It cradles the human body in plump, shining tufts of upholstery amid deep-pile carpeting. With each passing day, however, the car becomes less attractive: The paintwork chalks and fades. Any scratch or dent in the sheet metal is immediately visible as a prominent blemish. Rust spots mar the chromium. The glass and paintwork, because of their ultra-smooth surfaces, tend to look even dirtier than they really are. The upholstery sags and the carpets accumulate dirt that refuses to be coaxed out. A motorist who buys a car for its visual appeal is doomed to a life of constant maintenance and ultimate disappointment, because the car will never again look as good as it did on the day it was purchased.

Consider, by contrast, a sloping roof made of cedar shingles. The shingles are somewhat garishly colorful when installed but rather quickly begin to turn gray in the sunlight and rain. For some months they are not very attractive but look a bit dirty and streaky. Then the colors begin to blend and deepen, and the roof takes on a comfortable, silvery gray tone that becomes richer with the passing years. Rain erodes the softer bands of spring growth from the grain of the wood and adds texture to the roof. Lichens or mosses may add color. With no maintenance at all, the roof will not only last for several decades but will actually grow more attractive each year. The automobile starts life with a perfection of finish that can only grow less perfect with age, whereas the cedar roof sidesteps the question of perfection entirely and acquires an ever-richer patina whose beauty has no limit.

There are many building materials that have this same quality. Redwood and cypress are similar to cedar in their weathering properties. Unfinished interior wood in tabletops, doors, and railings that is constantly handled and rubbed looks spotty for a time but then begins to glow with the natural polish given it by human hands. Brass door handles are etched chemically over time by the sweat of hands, to expose the fascinating crystalline pattern of the metal. Copper in the outdoor environment changes slowly from a bright, reflective orange metal to a rich tapestry of blue-green oxide. The oxide clings tightly to the metal to protect it from further deterioration. Lead roofs oxidize to a pleasant white. Aluminum is a metal with similarly self-protective oxides, but the oxides look dirty and streaky and are not especially attractive. Accordingly, most exterior aluminum is chemically oxidized in the factory, often with the addition of a permanent black or brown color, and becomes a material that grows neither better nor worse with age. Most ferrous metals rust destructively, but a steel alloy has been developed that forms a tenacious, self-protecting oxide and assumes a pleasing color and texture after an initial period of splotchiness.

Masonry generally looks progressively better as it accumulates grime and as the mortar weathers to a more subtle color. Climbing vines further enhance its beauty year by year. Unglazed ceramic tile floors or floors of natural stone slabs often wear into pleasing contours underfoot. Glazed ceramic surfaces on masonry change little in appearance over the years and present a bright counterpoint to the softening, deepening colors of the materials about them. Because age so often darkens colors, surfaces that begin life dark in color tend to age more gracefully than light surfaces do. If a surface of white paint or whitewash, however, is frequently renewed, it will in time become pleasantly smooth in texture and will show off to good advantage adjoining areas of darker colors.

Surfaces made up of many small units generally age more attractively and are easier to repair than large, smooth planes. A crack or flaw in a floor-to-ceiling sheet of glass is visually annoying, potentially dangerous, and requires a skilled crew and expensive equipment to replace. But cracks in a small pane or two of a large multipane window are not particularly disturbing to the eye and do not require replacement of the panes unless they leak water or air. If replacement is necessary, a single semiskilled person can do it with a couple of dollars' worth of materials. The large sheet of plate glass must be washed to perfection every few weeks if it is to appear clean, whereas the multipane window can get quite dirty before it becomes disturbingly so. Similarly, a courtyard paved with bricks or small stones has maintenance advantages over one paved in concrete or asphalt. A wall paneled in narrow wood boards is apt to age more gracefully than one made of large sheets of beautifully veneered plywood. A floor of irregular stones or primitive clay tiles shows less evidence of the ravages of time than does one of polished marble slabs.

Secondhand building materials offer many advantages with respect to their visual characteristics: They are already worn, weathered, and hardened by time. In many cases they have already acquired a pleasant patina. They are often richer in design and detail than contemporary materials. They are sometimes cheaper than new materials. And they generally bring a welcome sense of history and continuity with the past into a new building. They blend more and more naturally with the building as it acquires marks of the injuries, repairs, and changes of its own lifetime, to produce a structure that records its own history on its exposed surfaces.

Buildings should be able to absorb life's hard knocks without looking the worse for them. Normal weathering and wear should not diminish the beauty of the finishes. Reasonable amounts of dirt and grime should look quite acceptable on the various surfaces of the building. And the normal, pleasant clutter of the various objects of people's daily lives should not look out of place because the building seems to have been constructed for superfastidious visitors from another planet. Building maintenance is not an end in itself but is intended to make life more livable for the building's inhabitants.

Addition and remodeling are eventually important to the usefulness of most buildings. Through these processes, a building can grow and adapt to changing human requirements, and the useful life of a building can be extended indefinitely. Remodeling usually involves removing at least some of the interior finishes, partitions, and mechanical equipment of a building, reconfiguring the interior and perhaps the facades, and applying new finishes. Remodeling is more difficult if the interior has many load-bearing partitions or if the floor structure is difficult to cut and change, as it is in many concrete buildings. It is easier if partitions, floors, stairs, and mechanical services are relatively simple to demount and relocate.

Adding onto a building is possible in the horizontal direction, the vertical direction, or both. For vertical additions, much expense and disruption can be avoided if the original structure is made to accept additional floors without overstressing the columns and if elevators, stairs, and mechanical systems are planned from the outset to serve the extension. Horizontal additions are bound to look awkward if the original building is a complete, closed form like a dome, a cylinder, a cube, or a hyperbolic paraboloid shell. They are easiest to fit when the original building rambles a bit already and when one or more natural points of connection are provided along the periphery of the existing pedestrian circulation system.

Re-Use of Buildings

Buildings can adapt well to changes in use over time. We continue to live, study, worship, and conduct business in buildings that in many cases are centuries old and that have had to change many times over that period. Re-use is easier if the building has large, unobstructed, rectilinear spaces, movable partitions, and readily accessible mechanical and electrical components. It is more difficult if the building has load-bearing interior partitions, short structural spans, or a form that is very specific to a particular use, such as a chapel or theater.

With periodic remodeling and constant maintenance, a building can live for a very long time. A number of buildings from Roman times are still in use. Even a wooden building, if kept safe from water and fire, can last for centuries. But buildings are abandoned or torn down every day. Sometimes health or safety problems are the reason. Sometimes a building simply cannot be brought up to modern standards of convenience because it is too small or its original configuration is too unyielding to alteration. More commonly, a building becomes uneconomic, through changing needs of its occupants, excessive costs of maintenance and repair, or because it occupies a piece of land so valuable that the owner wishes to build a much larger building in order to maximize the return on investment. In most such circumstances, the building is dismantled and trucked away in pieces by a building demolition contractor. Some of its components may be saved and sold, but usually the entire building ends as broken chunks in a dump.

In rural areas it is not difficult to find a barn or shed dying a natural death after many years of service (21.5). It is sad to know that the optimism, human energy, and skill that originally went into the making of the building are now to be lost forever, but it is a joyous experience to see how Nature takes back the building materials it once yielded, to convert them to other uses. There is dignity in the sagging of decaying wood and reassurance in the slow absorption of the wood by the earth. There is beauty in the gentle, supremely patient attack of Nature on masonry and concrete, as weather softens the surfaces, and tendrils of plants reach into tiny pores and cracks to begin the long process of prying and wedging that will someday, probably lifetimes hence, reduce even these materials to earth. The plants gradually cover the dying building with a shroud of green leaves and bright blossoms, and it becomes a new object in the landscape, a picturesque promise of the new and better order with which Nature will replace it.

Further Reading

Mohsen Mostafavi and David Leatherbarrow. On Weathering: The Life of Buildings in Time. Cambridge, Mass., the M.I.T. Press, 1993.

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