Windows (10/19/17)

Excavation and pile-driving along the 3rd Street side of the project has reached Holy Rosary Church, and construction of 250 Massachusetts Avenue has reached grade at the north end of the building. A new Tower Crane will be erected next week to begin pouring concrete farther south. A skylight has been installed at 200 Massachusetts Avenue and mechanical, electrical, and plumbing systems line the ceilings on most floors. Water fountains are beginning to appear and at least some of the elevators are operable. The utility penthouse is mostly enclosed and drywall gives shape to many of the interior-core walls on several of the floors.

There is a strange quiet on some of these floors as workers move off to other floors to continue their tasks. As I walk the floor alone, I can begin to envision the offices and the people who will soon inhabit these rooms. With a little imagination, the quiet gives way to the echoes of the voices of those who will work in the building in the now, not too distant future.

But it is the windows, now reaching to the top of 200 Massachusetts Avenue, that demand our attention. With the glass curtain wall reaching to the top of the building, work will commence next week on the storefront glass that will line the lower floors. Soon the building will be enclosed, permitting interior finish work to begin.

Twelve thousand years ago, windows were unknown. Nomads built their beehive-shaped huts from stones or slept in tepees and lean-tos made from branches and skins. Holes at the top dispersed smoke rising from a hearth and sometimes provided the only means of access. Windows served no purpose to the ancients. They let in weather and spirits, allowed enemy eyes to peer inside, and complicated the construction of dwellings that had to be erected, torn down, or abandoned quickly as the nomads moved from place to place.

Windows, though not as we know them, may have been developed by the Paleo-Eskimos who lived in the Arctic 6,000 years ago. Living on the edge of glaciers, the Inuit would set translucent, freshwater ice blocks midway up the domes of their igloos. These “windows” let in light but still kept out the cold and roving prowlers of human, animal, or divine origin. Sadly, the origin of the igloo has been lost in antiquity so there is no way to verify its date of origin. The Inuit living away from the ice in branch homes often used translucent animal gut, bladders, or skins to the same effect.

As villages and small cities evolved in Mesopotamia around 7,000 B.C.E, permanent rectangular houses began to appear and windows became more important. Because cities permitted a collective defense against enemies, windows posed less danger than they did in nomadic times. Moreover, large numbers of people living in small and connected houses in warm climates needed more air flowing into their homes. The oldest known depiction of any city or town in the world is a painting from Çatalhöyük in what is now Turkey, dating to somewhere in the 6200 B.C.E. range. It is also the oldest known representation of architecture in the world. Windows are clearly seen in the painting. Archaeologists also believe that it documents a specific event — an erupting volcano near the site of the city. If you are interested in learning more about the excavation of Çatalhöyük, you can visit their website at

Painting circa 6200 BCE | Modern Interpretation

Wall paintings from Egypt and reliefs from Assyria show openings in house walls covered with matting that could be rolled up or down as the weather required. In some places, thin slices of mica, selenite, or other varieties of gypsum provided a more permanent window barrier. Citizens of Crete in 2,000 B.C.E. had large windows and used transoms (a crossbar of wood or stone dividing a window horizontally) and mullions (a vertical member between the panes of a window). Given the richness of Crete, the windows were probably made from alabaster; but this, like so many other parts of Minoan culture, remains lost to modern research. While the people of Crete were looking out from their homes, the Greeks forswore windows to preserve their privacy. They built their homes as a series of single rooms with doors, but no windows, opening into great courtyards. Neither were windows placed in the outside walls of their homes. It is of no small cultural significance that the ancient Greek word for the human eye meant the “window to the soul,” connoting the privacy of thought and revealing, perhaps, another example of the relationship of architecture to many aspects of Greek life.

Minoan Culture Street Scene from Santorini

As they did with so many other architectural innovations, the Romans improved on the windows they found in other cultures. Glazed windows begin to appear in Imperial times. Fragments of greenish-blue glass set in bronze frames have been found in Pompeiian houses, and large clerestory windows (a row of windows in the upper part of the wall), filled with shell, marble, mica, and perhaps glass, were used to retain heat in the Roman baths. The Romans also built greenhouses to raise crops in winter. Such amenities, however, were the province of Patricians. Windows were not essential to most early Romans until they developed apartment buildings, some of which rose to six stories. In modest apartments, windows were usually covered by wood shutters, vellum, or oiled cloth. Better apartments featured mica or gypsum in the frames. By the second century A.D., glass was hardly a luxury in the major Roman cities.

Reconstruction of a Pompeian House | Roman Blue Glass

Windows appeared in the first century A.D. in China but the use of glass was late in developing. Though the earliest evidence of glass materials appears during the Zhou Dynasty 1046–256 B.C.E. and glass as we know it was widely common during the Han Dynasty 206 BC–220 A.D., traditional architectural choice generally excluded it as a construction material. Instead, the Chinese made windows with wooden grills covered by silk paper. Later they made the paper for the windows from rags, tree bark, and plant stems. These windows reached Japan in the 7th century A.D. where they developed into magnificent shoji screens made with sliding wood panels and paper windows. These simple yet elegant screens still adorn homes in Japan today.

As the barbarians sacked the Roman Empire, much of its glass industry was destroyed along with everything else. Most of Europe returned to cloth, skin, and wooden window coverings. Castles and keeps rejected large windows and replaced them with slits in solid walls, large enough to permit arrows to fly but small enough to protect the archer. Nonetheless, windows did not completely disappear in medieval Europe. Primary glass production sites continued to operate in the Near East, far from the collapsing western Empire. In time, wood-ash glass developed in what are now the United Kingdom, Germany, and France, reducing the independent monarchies’ dependence on the Near East producers.

Because of the continued production of glass and the development of new technologies, glass continued to adorn both western and Byzantine churches. Hagia Sophia, built in Constantinople in 532 A.D., uses pierced marble frames with panes of glass. Islamic builders in Egypt and Syria also used this technique but used cement frames instead of those made of marble to gain greater technical freedom and hence, richness in design. They added small pieces of colored glass to produce brilliant light patterns. Because the climate was warm and dry in those regions, frames were also often left empty.

Hagia Sophia (Picture on the left by Marius Becker)

The Islamic design patterns were subsequently copied in Europe in the twelfth and thirteenth century. Using lead cames (slender, grooved bars of lead for holding together the pieces of glass in stained glass windows) and stained glass inserted into frames and mullions of stone instead of marble or cement, medieval builders and bishops ushered in an architectural explosion of Gothic cathedrals. The Cathedral at Chartres, now a UNESCO World Heritage site, is a masterpiece of French Gothic art, as much for its windows as for its flying buttresses and stone sculptures. Abbot Suger, arguably the creator of the first Gothic building, best understood the power of architecture to transcend the temporal and connect the world we inhabit with the world of the spirit. Suger rebuilt the abbey church at San Denis, north of Paris, in the 12th century using innovative structural and decorative features. In doing so, he is said to have created the first truly Gothic building. Because few people could read at the time, the stained glass windows of St. Denis “told” parables and other stories from the bible in a visible vernacular, enabling the illiterate populace to understand their faith and see God’s creation on earth. In Suger’s words, stained glass windows had the power to “urg[e] us onward from the material to the immaterial.”

The Great Rose Window of Chartres ( Photo by Eusebius (Guillaume Piolle)) | The Windows of San Denis

Nobles, recognizing the richness of glass, slowly abandoned their fortified castles. Not until the 1500s, however, were England and France safe enough to turn the castles into chateaus and manor houses, built with proper windows for ventilation and light. During the Renaissance, windows conformed to classical proportions, often divided by a single mullion and a single transom forming a cross. Large casement windows extending to the floor, commonly known as French doors, also were developed in the Renaissance and became the standard window in Europe. Windows were often decorated with architraves (the lowermost member of a classical entablature resting upon columns), cornices, and pediments (the triangular piece resting on the architrave), sometimes with pilasters (a shallow rectangular feature projecting from a wall, having a capital and base and usually imitating the form of a column), and columns at their sides. During the Baroque periods, these ornamentations reached the height of elaborateness. Ancient fears had fallen away by then and the window became a permanent and welcome design element for the modern world.

Classical Entablature
Renaissance Windows | Baroque Windows

Tourists visiting stately English homes today will notice that palaces from the Elizabethan era have larger and more expansive windows than buildings from any other period of English history except the modern. Queen Elizabeth I held the monopoly on glass production in England. Her most loyal supporters installed large windows in their palaces to show support (both political and financial) for the monarch. The demand for glass, however, surpassed Elizabeth’s ability to produce it as the timber used to fire her furnaces ran out. Much of the seventeenth-century English woodland had been cut down for energy, and coal was only then emerging as a source to power the furnaces. Moreover, few Englishmen were skilled in glassmaking. Thus, much of England’s glass had to be imported from other regions of Europe.

Late Tudor commercial policies concerning glass affected the exploration and settlement of the New World. Elizabeth saw the New World as an energy resource for her furnaces and to that end, sent Polish and German glassmakers to the Jamestown colony in 1608 to produce glass. These artisans produced the first factory-made products on the North America continent. For reasons that remain obscure, this first attempt to create a glass-making industry failed. Another was organized in 1622, but the imported Italian glassmakers “fell extremely sick” and the venture ceased by 1624. Nonetheless, the introduction of coal to fire the English furnaces reinvigorated the glass industry. The first successful colonial glass-making industry was developed in New Jersey in 1739. Glass windows became common during the eighteenth and nineteenth centuries, and the English vertical-sliding sash window and the double-hung window became the standard in the United States. The double-hung sash window technology has remained virtually unchanged since its development.

European glass in Elizabethan times did not resemble the glass we use for windows today. Most early window glass was produced by the “crown process,” developed by the Normans in the Middle Ages.

Glassmaking Furnace at Jamestown — Circa 1609 | Crown Glass Production

Crown glass is produced by blowing a mass of liquid glass into a globe at the end of blowing iron that is then marvered (rolled on a hard, flat surface of stone, wood, or metal) to a conical shape. A pontil rod is then attached to the other end and the blowing iron is cracked off, leaving a jagged opening. The glassmaker then places the globe into the “glory hole” (the mouth) of the furnace and reheats it, all the while spinning the soft glass to keep it from sagging. “At some point, centrifugal force [from the spinning motion] causes the globe to flash into a flat disk, which grows larger as the spinning continues. Upon cooling, the disk [is] cracked off the pontil rod.” The glass produced by the “crown method” is not truly flat. Concentric circular waves emanate from a thick center. In the middle of the disk is the crown, the point where the pontil formerly was attached. The crown method could not produce large sheets of glass but it did create panes large enough for early windows. Many buildings remaining from the colonial era still have windows made from the crown method. Such glass is prized today, especially if it is original; but it is generally used now as a decorative element rather than a functional one.

Crown Glass

Broad glass was developed in medieval times using a process that continued to be used with variations into the twentieth century. In 1832, the British Crown Glass Company adopted the cylinder method to produce sheet glass using the expertise of famous French glassmaker Georges Bontemps. This glass was produced by blowing long cylinders of glass. These cylinders, often as much as fifty centimeters in diameter and 175 centimeters long, would then be slit when cool and gradually opened with moderate reheating to become flat. Glass made from this process was flatter than crown glass and did not have the telltale crown in the middle; moreover, it could be made in much larger pieces. The Crystal Palace, built by Joseph Paxton to house the Great Exhibition 1851 in London, demonstrated the extraordinary use of glass as a building material. The Crystal Palace ushered in the public use of glass as a material for domestic and horticultural architecture. The plate glass process, developed by James Hartley in 1847, used iron rollers to produce a sheet of glass, which, while still soft, was pushed into a temperature-controlled oven called a lehr, These sheets were often used for the glass roofs of greenhouses and railway stations.

The Crystal Palace
Claude Monet’s Gare Sant-Lazare

Henry Bessemer, best known for automating the steel industry, also patented a system in 1848 whereby a continuous ribbon of flat glass was formed by forcing the molten glass between rollers. This process was expensive since all of the surfaces of the glass had to polished. Bessemer also introduced an early form of “Float Glass” in 1843. Float glass involves pouring molten glass onto liquid tin — thus floating it until it cools and solidifies. Bessemer’s process was early form of the float glass method that is still in use today. By the end of the 19th century, innovations in glass- and window-making were advancing rapidly. In 1888, the Chance Brothers industrialized the production of cylinder glass in England when they introduced a machine rolled glass method. Their glass was relatively inexpensive to produce and was of high enough quality to make clear windows with minimal distortion.

At the dawn of the twentieth century, Émile Fourcault of Belgium and Irving Colburn of the Libbey-Owens Glass Company in Charleston, West Virginia, each invented a process that greatly improved the glass rolling process. Nonetheless, like glass from earlier processes, theirs had to be ground and polished for optical clarity. Finally in 1959, Alastair Pilkington introduced a float glass process in England that eliminated the need for grinding and polishing, and produced glass with modern-day clarity.

Structural glass and steel curtain walls evolved rapidly between the construction of the Oriel Tower Chambers in Liverpool 1864 and the construction of the first glass box buildings, the United Nations Building and the Lever House, in New York in 1952. The glass curtain walls used in Capitol Crossing, using glass made with the Pilkington process, epitomize the maturity of glass windows as a structural architectural feature. 200 Massachusetts Avenue uses both storefront and curtain wall systems. Curtain wall usually refers to a non-load bearing, aluminum-framed system carrying glass, panels, and louvers that form the exterior wall of the buildings. Storefronts are non-load-bearing glazed systems that are found on the ground floors of building, usually used for retail spaces. Almost 1900 windows will be installed in 200 Massachusetts Avenue. The windows on floors four through thirteen are five-feet wide by ten-feet, nine-inches tall. Triple span windows — meaning that one unit covers three floors of the building — will be installed at the east and west main entrances to the building. Double span units will be installed at the entrances to the retail units along Massachusetts Avenue, and single span storefront units will be installed along the rest of the first floor.

Oriel Chambers (Liverpool, England, 1864) | United Nations Building (New York City)

If this project occurred last century, most likely all of the components of these windows would have been manufactured and fabricated in the United States, probably in the same city. Globalization, however, has changed the way buildings are constructed. Although some of the window components will be manufactured or fabricated in the U.S., four other countries are critical to producing the windows for Capitol Crossing. The glass for the windows is produced by a company called Tvitec, a relatively new company with a main production facility located in Cubillos del Sil, a small town in northwest Spain. Despite its small size — fewer than 2,000 residents — it has one of the largest glass production factories in Europe and manufactures the largest sheets of glass in the European market. These sections of glass, called Jumbos, measure 3.3 meters by twelve meters and provide the glass used in Capitol Crossing. Tvitec’s glass-making furnace alone is more than 60 feet long. The company has produced glass for buildings throughout Europe, South America, the United States, and even in some places in Asia and Africa. If you are interested in seeing some of the extraordinary glass structures using their glass, you can view them at

Tvitec is one of the subcontractors of the main window fabricator, Permasteelisa North America, a division of the Permasteelisa Group. It is a conglomerate of more than fifty companies in thirty countries with headquarters in Vittorio Veneto, Italy. Project architect, KRJDA, created the drawings of the building which were sent to the Miami engineering division of Permasteelisa where the window system was engineered. Every screw, spacer, and gasket was carefully designed for each piece of curtain wall. Even the shipping crates are designed by engineers. Once the window design is engineered, the panes of glass are produced in the furnaces in Spain. Modern glass is produced by the float method, the process developed and patented by Sir Alastair Pilkington in 1959. Prior to the development of Pilkington’s process, glass was produced by a drawing method whereby the glass passed through rollers. The drawing process, however, resulted in roller waves and other distortions in the glass. The resulting glass had to be ground and polished which was time-consuming and costly. Pilkington’s process transfers the glass at temperatures around 1050 degrees Centigrade from the melting tank onto a bath of liquid tin where it cools to a temperature of 600 degrees Centigrade. The glass produced in this fashion has no distortion. Despite many efforts to do so, no one has been able to create a better method.

Sir Alastair Pilkington; 1920–1995 | Pilkington Factory in England

Once completely cool and solid, the sheets are cut to size, coated, heat treated to make them stronger and more impact resistant, and fritted. Fritting is a process whereby particles, often ceramic beads, are applied to the interior surfaces of the window. Sometimes the frits are difficult to see by the casual passerby. Other times, they may appear as different colors when viewed from the inside or the outside. The glass used in Capitol Crossing is fritted to block solar radiation, to protect curious birds, and simply to create a pattern.

Fritted Glass

Tvitec produces three panes of various thicknesses for each window. Argon gas fills the space between the panes which are then sealed with silicone and left to cure for three days. The three layers of glass create high energy efficiency and noise transmission resistance. After three days, the glass is assembled into insulated units and shipped to Permasteelisa in Connecticut for assembly in the window frames. The shipping process was delayed on this project because of dock worker strikes in Europe. It was also delayed because Atlantic Ocean icebergs were floating far to the south of where they would normally have been at that time of year. Ships carrying manufactured goods from Europe to the United States had to detour almost 500 miles to avoid collisions with the floating ice. The effects of global warming turn up in the strangest places.

While the glass is being fabricated in Europe, the extruded aluminum frames are being made in Texas. Aluminum is used because it is strong and lightweight and maintains its stability under extreme weather conditions and temperature changes. Because it is impervious to humidity, temperature, and warping, aluminum doesn’t rust, shrink, or swell. The extruding process refers to taking a billet, that is, a solid cylindrical block of molten aluminum, and heating it to 900 degrees Fahrenheit. The softened but still cylindrical billet is loaded in a press where it is forced through a die to create the proper shape for the frame that will ultimately surround the glass. The extruded aluminum is then cooled, straightened, and aged to maximize its strength. It is then cut to the specified dimensions of the window. Finally, the extrusions are painted, which for some larger extrusions, takes place in Canada.

Aluminum Billets | Extrusion Press from Yuen-Sun Equip. Co.

There are many parts of the window yet to be considered. The stainless steel cladding, that is the bright metal surrounding the windows as we look at them now, is sourced from Finland and fabricated in Italy. The little parts, gussets –plates for uniting structural members at a joint in the steel frame — caulk, screws, washers, gaskets, and spacers are all being fabricated at the same time. To ensure that the windows as fabricated meet the engineering and architectural specifications of the design, four separate mock-ups of the windows are conducted in various locations to ensure their appearance, engineering, and performance. They are then tested in West Palm Beach, Florida, to ensure they can sustain the wind loads of up 120 miles per hour at three-second gusts and the structural deflection of ¾ of an inch that the windows will endure once they are mounted on the building. Testing the wind loads requires building a mockup of the curtainwall and using large propeller engines to generate the winds required by the specifications. Once the engineers and architects approve the final design, all of components of the window come together in Hartford, Connecticut, where they are assembled in the factory of Permasteelisa North America. The finished windows are then shipped to the site where they are installed.

Wind Testing to Simulate Wind-driven Rain Hitting the Building Using an Old Airplane Engine

Soon those windows will give us entry into the lives of the people who occupy Capitol Crossing and allow the occupants to see and wonder about us. After a while though, we will hardly notice them and they will see us mostly in a blur. In the modern era, windows are everywhere. But because they are ubiquitous, they soon become ignored as we pass them every day — lives within, lives without — passing in an almost unrecognizable dance. Windows… windows are everywhere, and as the Greeks surmised, they offer a glimpse into the soul. They unite us and separate us from friends and casual passersby alike. They surround us in our homes and workplaces; they seal in warmth on wintery days, and bring sunlight to a gloomy room. They beckon to our neighbors but when shuttered, hide our private lives as we seek a solitary moment. Windows open us up to distractions in our world. Through them, we watch the joys and sorrows of the world, allowing us to daydream into the lives of strangers. Do not take windows for granted; do not ignore the unlimited possibilities they offer. As you do, remember the admonitions of Edith Wharton who once reminded us to

“Set wide the window. Let me drink the day.”


Wells Turnage, Project Executive for BBC Construction and Jason Spencer, Assistant Development Manager at PGP Development LLC provided technical assistance for this Construction Note.

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