Green Roofs

Did You Know?

Cool roofs have similar benefits to green roofs in that they reduce internal building temperatures, increase occupant comfort, decrease cooling loads, lower energy bills, and increase the life expectancy of the roof.

What to Consider Before Installing a Green Roof on a Historic Building

The first issue to resolve when considering any green roof is, “What is the primary purpose for installing a green roof?” Is it primarily for energy efficiency, for storm water control, for heat island reduction, for visual enjoyment, or other reasons? Considering the underlying purpose will shape the next decisions in designing the green roof and help determine if a green roof is an appropriate solution at all.

The most important thing to keep in mind is that a green roof should not negatively impact the building’s historic character. Integrating a green roof into a historic building rehabilitation project may appear to be an easy solution to reducing the urban heat island effect, improving storm water management, and improving the energy efficiency and sustainability of the building. However, while there can be many benefits to a green roof, there are specific issues that must be considered before installing one on a historic building. Preservation of the historic resource itself should always take priority over any perceived benefit that might potentially derive from the addition of a green roof (or any sustainability measure). Installing a green roof can also require major changes to a building. If it should have to be removed at some time in the future, for instance to repair the roof membrane below, its removal should not damage the historic building.

The energy efficiency benefits of a green roof would be outweighed by any existing deficiencies in the building envelope or Heating, Ventilating, and Air Conditioning (HVAC) equipment. These must be corrected before installing a green roof. An energy audit will evaluate the building’s current thermal performance and identify any repairs that need to be made. Air infiltration should be reduced, any necessary HVAC upgrades should be carried out, and insulation should be added in appropriate locations. If the budget allows, an energy model should be conducted to predict the potential impact of a green roof. This can assist the owner of a historic building in deciding whether installing a green roof would be cost effective and if it would provide any added environmental benefits. Because of the many factors that must be considered, the decision to install a green roof should be made with the guidance and expertise of a multidisciplinary team, consisting of a structural engineer, landscape architect, and a historic preservation professional and/or a preservation architect.