Historic Preservations and Green Buildings

Historic preservation buildings have customarily grown up with the community which built them and have often become fixtures for a century or more. In certain stories, historical buildings are characters themselves and are as important to the plot as the protagonist. That’s not to say an old building can’t get some modern attributes, as that is the growing theme with green roofs on historical preservation buildings. Why just get a historical roof restoration when you can get a green roof?

What Is a Green Roof?

A green roof is a layer of plants or flora which is planted over a waterproofed system installed on a flat or slightly askew roof. These roofs are also known as vegetative or eco-roofs. The major purposes for installing a green roof are to achieve environmental benefits,1 including improving the air quality, reducing storm water runoff, saving energy, cooling the building, and reducing the temperature in the surrounding environment, especially in urban areas.

Green roofs fall into three groups:

  • Extensive Green Roof: These typically have a depth of 3-5 inches and have a maximum weight of 15-25 lbs./square feet. The plants are mostly mosses, sedums, herbs, and some grasses. One of these is low maintenance and has a lower cost.
  • Semi-Intensive Green Roof: This type of roof is between 5-7 inches in depth and weighs roughly 25-40 lbs./square feet. The plants are mainly perennials, sedums, grasses, and shrubs. Instead of being a low maintenance roof, this acts as a habitat.
  • Intensive Green Roofs: These roofs are 7 inches and deeper, and they weigh at least 35 lbs./square feet. These consist of lawns, rooftop farms, shrubs, and trees. These fields automatically irrigate/flood themselves, and they are ideal for making a park or a garden.

The Rise of Green Roofs and Government Buildings.

Green roofs are being used on historic buildings because they enhance their energy-efficiency and sustainability. Granted, a green roof doesn’t fit on some historic buildings, but the ones it does fit on can make a major difference in reducing the temperature on the roof. The U.S. Government, which owns many historic buildings, began to reinvent its real estate by transforming buildings into more energy-efficient establishments.

One of these National Historic Landmark buildings is the U.S. Coast Guard Headquarters in Washington, D.C. The building was designed to be low and blend into the hillside. That hillside forms a portion of the “green bowl” around the District of Columbia. The green roof is expected to reduce the urban heat-island effect and add insulation to the roof, which cuts down on heat gain. Since its location is also a courtyard, occupants can enjoy the public space and enjoy the scenery. This is the second-largest green roof in the USA, and the 3rd largest in the world, with 557,000 square feet.

To date, over 100 historic buildings have been transformed in this way. Elani Reed at the U.S. General Services Administration (GSA) believes that “sustainability and preservation must go hand in hand” in terms of preserving a historic building and making it greener at the same time.

One of the key things to consider is the building’s structure itself. A green roof does increase the weight on top of the building, and it adds moisture and the potential of root penetration through the waterproofing layer. These issues must be addressed, and the Secretary of the Interior’s Standards for Rehabilitation must be met before a green roof can be added. Most importantly, it cannot alter the structure of a historical building, and any vegetation cannot be visible above the roofline from the public view.

With that, a green roof can be a welcome addition to a turn-of-the-century building and improve the environment at the same time. More government buildings are expected to undergo this process, as the documented benefits are almost too good to be true. Besides, just because a building has been in a community since the late 19th century, it doesn’t mean it can’t include 21st century innovation.


  1. http://www.gsa.gov/portal/mediaId/158783/fileName/The_Benefits_and_Challenges_of_Green_Roofs_on_Public_and_Commercial_Buildings.action (page 8)
  2. http://www.greenrooftechnology.com/green-roof-types
  3. http://www.nps.gov/tps/standards/applying-rehabilitation/its-bulletins/ITS54-GreenRoofs.pdf
  4. http://www.gsa.gov/portal/content/188591

Contact us today to learn more about green building and historic roof preservation!