Or: an essay on the preservation issues & solutions of flat roofs from the Modern movement

Background

The use of flat roofs can be found as far back as the Neolithic period in Scotland as well as more monumental examples which can be found in Egypt. One such site is the Temple of Hatshepsut from 1458 BCE which is still viewable today. Architectural styles since these early structures have employed flat roofs in many ways. These traditional flat roofs usually have a small angle toward the exterior of the structure in order to shed water effectively. In more recent history, flat roofs all but vanished from use with most new construction from Victorian to Beaux Arts. The styles of the 1600s to 1800s tended to favor pitched roofs for their practicality. These architectural styles may use flat elements, but the overall design rarely used a flat roof. This was until the “Modern” movement took off at the beginning of the 20th century. With the introduction of the Bauhaus and subsequent schools of thought, the use of flat roofs became more frequent than perhaps ever before. The flat roof in the Modern period was admired by many architects for its purity of form. Some notable architects who used flat roof systems in the Modern movement include: Le Corbusier, Ludwig Miës Van Der Rohe, Eileen Gray,  Jane Drew, and Frank Lloyd Wright after he abandoned the Prairie Style. However, these flat roofs were not always executed to perfection. In many cases, these designs considered the form of the project over the function. The Modern movement was more interested in the present moment, and the progression of architectural theory than it was in longevity of its creations. This is shown in the use of flat roof structures. Flat roofs are not very good at most things, and they are really only useful when they are also an extension of usable space.

Flat roof structures are inherently less efficient at shedding water or bearing snow loads. Miës’ Farnsworth House and Corbusier’s Villa Savoye were famous for the letters of their owners complaining about the rain coming inside. Dr. Farnsworth's frustration with Mies led to a trial between the two. In both examples restorations have taken place multiple times. It seems that the extremely low pitch angle has only hindered these examples and others from the modern movement. In these examples, limited drainage systems created pooling water on the roofs, leading to catastrophic damage, and making the projects all but uninhabitable. Another factor was the sealing methods which were not as advanced as they are today.  Of course, leaking roofs are not a problem that is exclusive to flat roof buildings, but the problem does seem to be more prevalent in them. As more and more of these Modern sites become eligible for historic designation, preventing leaks will become even more important for preservationists and restorers to understand. 

The Bauhaus

Founded by Walter Gropius, and continued by Ludwig Miës Van Der Rohe, the Bauhaus was founded to change the way in which architecture was taught and, on a larger scale, how it was understood. This school of thought rejected the ideas presented by the Beaux Arts and all other popular styles,  setting themselves apart with pure-form architecture lacking in ornamentation and traditional forms. Architecture in the Bauhaus was becoming more personal to the architect, and less interested in copying or re-creating historic elements. This new school of thought can first be seen in the Fagus Shoe Factory by Walter Gropius and Adolf Meyer in 1912.  

This building by Gropius and his partner predates the Bauhaus School, but it shows the direction that he would eventually bring over to the new institution. It has a flat roof and box-like shape which would become synonymous with the word modern itself. The entrance is off center, clearly rejecting the symmetrical designs of the Beaux Arts and Art Nouveau architecture. To the side of the entry, the stairs are visible from the over-sized windows, flowing up without any support pillars, a sight to be seen in 1913 when the building opened. Gropius would eventually leave Germany in 1934, heading to London first before accepting an invitation to become a professor at the Graduate School of Design at Harvard University.  

With this move to the States in 1937, Walter Gropius built a new house which would become America’s formal introduction to the Bauhaus movement. The Gropius House, as it would soon be know, was a flat roofed structure in Lincoln Massachusetts. The large overhangs merge into the center of the house releasing water into a dry well below the foundations.  The flat roof sets the building apart from its neighbors and compliments the other elements of the design. Over the years at this property, multiple restoration projects have taken place including ones to fix roof leaks. The issues seemed to be caused by pooling moisture. Similar problems would face new construction with the domination of Modern architecture over the coming decades. 

Gropius’ collaborator and successor at the Bauhaus school, Ludwig Miës Van Der Rohe, would also eventually move to the United States to avoid conflict with the Nazi regime. Miës would go on to create some of the most important buildings in the Modern movement. His personal style changed little during his career, with a focus on planar and linear forms coming together in almost classical arrangements. The space and order of his plans emulate temples found in Vitruvius and other classical sources. Examples such as the Seagram Building in New York go as far as to include ornamentation, but they do so to a limited extent in order to preserve the purity of the building’s form. 

Miës’ magnum opus is the Farnsworth House in Plano, Illinois. The structure of the house is based on small pillars much like Corbusier’s pilotis. It raises above what was then the flood plane of the area in two levels. The first level forms a large terrace with five more steps leading to the house’s main level. Miës’ appreciation of materiality is seen through the travertine floors and exotic wood on the interior of the project. Unfortunately for Miës, the flood plane of the area has changed and the house has been flooded multiple times leading to extensive damage to the structure. However, this flooding has little effect on the flat roof. The roof has also seen water damage, with the plaster ceiling failing in some areas from leaking problems.

The issues with the roof are seen through roof sections provided by Columbia University’s website. The roof is built out of materials which were still in their infancy at the time of construction. Atop pre-cast concrete there is a layer of foam glass insulation, with a waterproof membrane on top. The image also clearly shows the main issue with the roof, its slope. The outer edge of the roof slopes inward, much like the Gropius House. This slope leads to a single drain that exits through the utility stack and the raised platform below. While this elegant concept keeps rainwater from dripping over the side of the structure, it also means that draining can be inhibited. The pipe can easily be clogged from tree debris in the fall and ice in the winter. Most notable is the membrane, most likely a glass fiber or polyester. Whatever material it was, it would most likely not be able to handle the prolonged snow coverage that Northern Illinois winters provide. While the system seems to handle the weight of a winter snow, the slow thawing of the gathered snow would prove to be detrimental to the waterproofing from the time. The materials from the 1950s simply cannot compete with modern silicone waterproofing used today.  Using modern silicone would have all but cured the leaking roof issues the Farnsworth House has faced. 

The Five Points

Le Corbusier rose to prominence around the same time as Miës. In his early career in France, Corbusier revealed his vision for the modern world with the release of Toward an Architecture in 1923. The book examines the modern technologies available to view for the time period such as steam liners which would influence the Art Moderne movement, as well as factories and automobiles. Corbusier was fascinated with the rise of the automobile which allowed people to live further from the city than normal, hence the “Villa” in Villa Savoye. The manifesto also lays out the Five Points of architecture that make up Corbusier’s dive into Modern architecture. The most notable implementation of these points is at Villa Savoye in Poissey France, just outside Paris. The structure appears to float off the ground due to the slender pilotis and green first level, protected by the overhanging second level above. The structure is focused around a ramp which leads from the garage to the roof top terrace. The shapes on the very top layer are abstract, resembling ocean liners that Corbu praises in his book. The terrace is one of Corbusier’s most intriguing additions  to the Modern movement. The use of these terraces can also be seen in other buildings that Corbusier designed in this time frame including the Unite d’ Habitation outside Paris, and the Villa Stein. The addition of this outdoor space means that the use of a flat roof has a real purpose extending beyond aesthetic preference, something that cannot be said about the Gropius House or Farnsworth House.

The practicality of the flat roof in Corbusier’s earlier work does not mean that his buildings did not face the same issues as his contemporaries. On the contrary, the history of Villa Savoye and its design issues is extensive since its creation in 1929.  Mme. Savoye was never a fan of Corbusier’s creation as far as a home setting. She consistently sent letters to Corbusier about the leaking roof, the noise of the rain hitting the skylight, and other issues that plagued the residence. She writes in one of the more strongly worded letters, “It’s raining in the hall, it’s raining in the ramp, and the wall of the garage is absolutely soaked. What’s more, it's still raining in my bathroom, which floods every time it rains.” Following World War II, the villa would be turned into a barn, as Mme. Savoye has started to cultivate the land surrounding the site. By the mid 1950s, the town of Poissey began to look to acquire the property, as land was in short supply in the booming Post-War economy on the outskirts of Paris. Word began to reach architects and others interested in preserving this early Modern building over the next few decades. The Museum of Modern Art had much to do with the raise in awareness in the property’s derelict state. 

Again, here one can see how the failure to properly dispose of rain water causes issues in Modern flat roof buildings. The roof itself consists of multiple concrete tiles placed in gravel. These elements are sloped to drain into a small drain. Much like the Farnsworth House, this drain could easily be blocked. At least in the Corbusier example, the drain is accessible to the owner. This being said, it must not have been enough if Mme. Farnsworth’s letters are to be believed. Modern waterproofing technologies have restored this residence into a house museum, which it seems to be more suited to than a residence. 

Le Corbusier went on to create many buildings that took on less block like forms. One of the most notable examples being Notre Dame du Haut. At this later Corbusier structure, the roof slopes quite dramatically in a sculptural form complimenting its base. Perhaps Corbusier learned from the determined letters of Mme. Savoye. 

Commonalities

In Villa Savoye as well as the Farnsworth House and Gropius House, there are common issues that plague the structures roofing systems. Each of these houses — as well as many from the period — have a roof pitch sloped to a central drain in an attempt to hide watershed. Contemporary designs with flat roofs often attempt a similar feat. However, contemporary architecture has the advantage of new silicone rubber materials that resist moisture penetration at a higher level than anything available during the time of the Modern movement. At the Gropius House, the water collects in a central drain, going through the walls of the structure to the driveway below. Much like the Farnsworth house, the central drain is not easily accessible by the owner, which means that water flow can easily be blocked by debris or ice. This inevitably leads to water pooling on uneven areas of the roof, which would permeate through the sealing efforts made by the materials available at the time. A similar problem can be observed at Villa Savoye, though much of it’s problems can be attributed to Corbusier not providing enough slope for water to properly drain. At this property, the drain is at least accessible to the owner, but it also seemed to have the most problems. These more serious issues of water infiltration are most likely because of the gravel and concrete tile system that Corbu uses on the roof gardens. This system can absorb and evaporate water, but obviously not at a quick enough rate.

Approaching The Problems

The question remains of what the best approach is for these Modern flat roof structures. Is it important to keep the original materials on the roof of these structures? One of the major issues facing all aspects of Modern buildings is that they were not really meant to patina and age in the same way that older brick and masonry structures were designed to. This is apparent in their structure and materials. It is no accident that the roofs of these buildings tilt inward. The architects do so to avoid runoff affecting the exterior of the structure, to keep it looking as new as possible. 

If the architect’s intent is to hide ware, it should not be considered inappropriate to use modern materials and techniques on areas that do not interrupt the parti of the design.  In many areas of Preservation, the most appropriate choice for renovation is to use materials similar to ones used at the time. For example, it is more authentic to re-create a failed plaster wall with new plaster work as apposed to drywall. However an argument can be made that authenticity is not expressed in the same way for Modern buildings. Buildings from this movement were interested in using the most modern construction techniques for the time period. It is only right to repair problematic areas with the most modern techniques and materials, especially when their use does not take away from the visual quality of the project. For the roofs of these buildings, this principle is of the upmost importance for the preservation of the site as a whole. If any of the Modernists had had access to new silicone materials for sealing flat roofs available today, they certainly would have employed them in their final designs. There are many modern roofing sealers available on the market today that are obtainable for even do-it-yourselfers restoring a Modern building. 

These silicone based products have many advantages. First of all, silicone can withstand ponding water for any amount of time. This alone would have saved all of these buildings from the pooling water damage that they have faced since their construction. They are not water based, meaning that there is really no chance of water penetration unless a spot is left uncovered. Their composition also means that they shed water more effectively than any product available on the market during the Modern movement. Silicone coatings need replacement every 15 years or even greater in some climates.  Silicone can also be used with or without roof fabric, leading to additional cost savings. Whats more, it can be found in white or black which can lead to increased energy efficiency. The white silicone can be used to reflect light in warm climates to keep heat off of the building, while in cold climates the opposite is true. 

Their are some issues with silicone based sealers. These include the products slickness, which is effective at shedding water; but also means that the surface it creates is not appropriate for publicly accessible areas such as the terraces of Villa Savoye. The surface of the finished product does have a distinct visual quality that is not homogenous with the materials used in Modern buildings. Effectively, this means that the product should only be used where it can be hidden under other elements, or where it generally will not be seen.

At a site such as the Farnsworth House, white silicone could be used on the roofing system to effectively stop any damage from pooling water. The Gropius House could undergo similar renovation to prevent further decay. At both of these sites, the roof of the structure is far above any site line, meaning that there is no negative visual impact created by the use of the product. At Villa Savoye, a layer of silicone could be placed under the gravel and concrete block that makes up the rooftop terrace of the building. This would be a time consuming process to be sure, as the blocks would have to be moved by hand and accounted for in order to replace them correctly. In the end though, this would lead to a lasting restoration which would be quite effective as the silicone would even be protected from UV rays by the replacement of the gravel, meaning it would last longer than normal. Of course, this process would not help parts of any building which had already been penetrated by water. These damaged areas would need to be looked separately and addressed accordingly. 

There may be spots of moisture in the concrete block of the Farnsworth House for example. These areas, and others where moisture is present would need to be thoroughly dried and tested for structural stability. Any moisture remaining in the roof structure would be trapped under a silicone layer, and the moisture would only be able to escape through the ceiling of the building. 

Conclusion

The architects of the Modern movement gave less thought to how buildings would stand the test of time than architects from previous generations. Instead, these designers were more focused on what techniques were innovative and what they though would progress their ideas of architecture forward. In many ways, their refusal to adhere to historic forms hindered the longevity of their designs. The most significant problem with these forms seems to be the flat roof, an element universal in Modernism. For the time period, the use of flat roofs is problematic, as the materials from this period were not advanced enough to cope with pooling water that stood for a period of time. This material problem is only compounded by the common use of a central draining system which sheds water inward as apposed to off the side of the roof. Because of these issues, many Modern buildings are facing leaky ceilings and roofing structural issues that are not seen in other historic structures to such a large extent. This is not to say that these architects were ignorant of their actions. On the contrary, in many cases they knew that their roofs would leak but overlooked it as they thought the issue was worth it for the forms that their buildings took. In many ways, these designers were simply ahead of their time, as the materials available to them were limited in what they could build with any sort of practicality. Now that time has passed and our access to new more suitable materials for flat roofs has become greater, it is only right for preservation efforts to save these designs as a whole with the use of our modern advances in materials.