Green from the Outside In

March 19, 2007

By Kimberly Doyle

Green on the outside of a building is possible beyond well manicured lawns. Thoughtful design of a building envelope can increase a project's sustainability levels.

Material Selection
The use of rapidly renewable, bio-based materials conserves resources and makes a big difference in the green rating of any building. While not commonly used for the exterior of most commercial buildings, resources such as lumber, bamboo, and even cork are efficient ways to boost sustainability. Rating systems like Green Globes (, an online assessment tool used by building owners to rate an existing structure's sustainability, award higher points when lumber harvested from third-party sustainable forests is used.

The Philip Merrill Environmental Center, home to the Chesapeake Bay Foundation in Annapolis, MD, received such points. Its external shading system made from salvaged pickle barrel wood allows for natural heating and lighting.

Energy Efficiency
Considerations for energy efficiency also play an important role in a building's sustainability. Design teams can have the biggest impact when working from the outside in, says Max Zahniser, LEED program manager for the U.S. Green Building
Council. Downsizing mechanical needs produces smaller HVAC price tags and improved user experiences, he says.

This was the case with the Hood River County Library in Hood River, OR. Designers crafted a natural ventilation system that relies upon the strong and constant summer winds of the area as well as temperature swings of up to 40 degrees F. Awning windows capture the winds, creating airflow without fans or ductwork. Air then exits the building through large, motorized windows operated by manual switch to give occupant control and allow night air to cool the facility.

Green roofs, a common building practice in Europe and now gaining popularity in North America, also improve energy efficiency because they prevent heat from moving through the roof. Jennifer Sprout, director of local market development at the Green Roofs Industry Association, defines green roofs as an extension of any roof with a specialized growing system. Required components include:

  • A high-quality waterproofing and root repellent system.
  • A growing medium that holds water and provides nutrients.
  • A filtering process.
  • A drainage system.

A 2006 study from Environment Canada showed that a typical one-story building with a green roof system reduces summer cooling needs by up to 25 percent when 3.9 inches of growing medium were used. When working in conjunction with solar panels, green roofs were found to lower the temperature surrounding solar panels, thereby allowing the panels to operate more efficiently.

Depending upon the plants and depth of growing medium used, green roofs also retain as much as 70 to 90 percent of summer precipitation that falls on them and 25 to 40 percent in winter by storing the water in the substrate until it is absorbed by the plants. This process substantially reduces the amount and flow of storm water runoff, resulting in reduced stress on area sewer systems. Additionally, Sprout says green roofs have proven to outlast standard roofs, extending lifespan from the average of 10 to 12 years to 20 years.

Site Considerations
Other considerations for sustainable building exteriors include the site itself. For example, while green roofs increase energy efficiency, they also work to decrease a site's heat island effect, which is mainly due to the expanse of hard and reflective surfaces that absorb solar radiation, reradiate it as heat, and create temperatures harmful to the environment. Green roofs and reflective gravel are alternatives to dark asphalt. Another option is to design the parking structure underneath the building so as not to expose it to light.

Designing sustainable projects means important considerations from every angle. Exteriors are an important part of the equation.

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