Sawtooth Roofs: Restoring Historic Urban Buildings with Unique Rooflines
Our company works on common repairs, and replacement of historic low slope roofs here in Washington DC. Those type of roofs are relatively common, ubiquitous throughout the majority of the downtown areas of Washington DC and most of the city. Flat roots allow buildings to be built side to side without access from all angles of the perimeter and exterior of the building. In this type of urban context, flat roofs have lots of advantages.
However, with even larger footprint buildings, specifically in historic times, another type of roof was common called a Sawtooth roof. This type of roof provides options for illumination from natural light and fenestration and ventilation that are not as easily available in a typical flat roof layout.
The sawtooth roof design, shown in the pictures above and below, named for its distinctive jagged-like shape, resembling the teeth of an upside down saw blade, was a architectural advent widely used in industrial and manufacturing buildings during the late 19th and early 20th centuries.
This roof configuration consists of a series of relatively low parallel ridges with vertical or near-vertical glazed surfaces on one side and a relatively high sloped surface on the other, creating a repeating pattern across the building’s width.
In the case of the roof shown here in these pictures, the sloped portion of each of the small roofs has a slope close to 8-12, which is about a 30° angle. At each of these small sloped roof surfaces, built-in series, the vertical part below works as a small wall system.
The primary purpose of Sawtooth roofs was to maximize natural light and ventilation in large industrial spaces before widespread electrical lighting became available. Even in dense urban areas, when a large building takes up an entire block area, the building can still have several exposed sides that allow windows which function for both fenestration and ventilation.
However when the building is so large that the center of the building is all the way in towards the center of the city block, the center of the building is then very far away from the facades and the corresponding windows. A sawtooth roof layout like this though can allow for light to enter, even in the middle of the building. Skylights provide a similar type of natural light, at least, but skylights are generally very limited in size because they cannot take up the entirety of the roof surface on a flat roof.
In the sawtooth roof configuration, vertical glazed sections, typically facing north in the northern hemisphere and here in this particular example, allow relatively consistent, indirect natural light to enter into the building’s interior while minimizing excessive direct sunlight and heat gain. This design was particularly beneficial for historic textile mills, printing facilities, and other industries requiring sufficient natural lighting. Most people would prefer living and or working in a building with more natural light in ventilation. The ergonomics and quality of work and life in the interior space is simply and obviously much better.
The sloped sections of the sawtooth design typically featured panelized roofing materials which were laid in typical sequence, starting low, similar to both modern roofing and historic low slope roofing on typical Washington DC row homes. This sawtooth configuration also created useful spaces for mechanical systems and ventilation equipment. The design allowed for air circulation, either from powered equipment or from articulable glazing / window systems, as the glazed sections could often be operable, creating a natural chimney effect where hot air would escape and cooler air would enter through louvers or windows at the exterior perimeter. This type of natural stack effect system helped regulate interior temperatures significantly.
In modern applications, sawtooth roofs have also experienced a bit of a revival in sustainable architecture, where they’re used in some examples of contemporary designs.
For the past 20 to 40 years, there has been a interest and push for green designs that use a lower energy footprint and work in a bit of a more autonomous type of way, resulting in a lower energy footprint. This sawtooth roof design and configuration can help to reduce dependence on artificial lighting and mechanical ventilation.
Contemporary designs also often incorporate solar panels on the sloped sections while still maintaining the natural lighting benefits of the glazed surfaces. Flat roofs simply work better in certain configurations, but not many flat roof layouts allow for both effective natural light and simultaneous, spatially adjacent solar panel installation for solar energy harvesting.
Like many historic buildings, here in Washington DC, this particular building needs to be renovated and revitalized, or it will sadly be demolished. Nothing short of extensive restoration would be enough to save this particular building.
Unfortunately, in many cases, historic buildings like this are often demolished by developers who are looking for a quick and easy way to get in and out fast and make money quick. It kind of makes sense, we’re a capitalist country and capitalism doesn’t waste any time thinking about the long term greater good in preserving the relics of history.
In the next picture below you can see an example of the typical windows installed at the side walls of these buildings. In historic times true divided light window frames were often used with single pane glass. This particular window has to be boarded up, on the internal side of the glass, at this time with missing pabes of glass, as the only way to cost effectively and quickly replace the broken parts of this window would be actual replacement, not refurbishment.
We recommend every building owner in DC who values the longevity of their roof (and their investments) and building use a contractor who values the simple and important principles of proper roof construction like Dupont Roofing DC. Learn more about our company and the proper techniques of working with roofing on historic buildings in Washington DC here on our blog at DupontRoofingDC.com, and you can call us at (202) 840-8698 and email us at dupontroofingdc@gmail.com. We are happy to help and at least talk through options.
