Exterior view of a building.

In 2011, the 7,200 square foot middle section of the Dirksen Senate Office Building roof was replaced with a green roof. What had previously been an unusable outdoor tennis court was transformed by plantings called sedums, which is a drought-resistant plant that stays green all year long. Installing a green roof more than doubles its life expectancy.

The middle section of the Dirksen Senate Office Building roof, prior to construction.

The middle section of the Dirksen Senate Office Building roof, prior to construction.

Removal of the lightweight concrete from the Dirksen Building roof.

The first step was to remove the lightweight concrete from the roof. 

The old insulation and waterproofing visible on the Dirksen Building roof after the concrete was removed.

Once the concrete was removed, the old insulation and waterproofing is visible.

Workers installing a filter fabric over a drainage layer on the Dirksen Building roof.

Next, workers installed a filter fabric over a drainage layer.

Workers installing a rigid insulation over the Dirksen Building root barrier, creating two inches of insulation.

Workers installed a rigid insulation over the root barrier, creating two inches of insulation.

A worker levels the soil on the Dirksen Building roof. At this point of the project, the gravel ballast for the walkways has been installed.

A worker levels the soil. At this point of the project, the gravel ballast for the walkways has been installed.

Workers on the Dirksen Building roof plant various types of sedums, a drought-resistant plant that stays green year-round. It has a shallow root system that allows it to grow in only four inches of soil.

Workers plant various types of sedums, which have a shallow root system that allows it to grow in only four inches of soil.

The Dirksen Building green roof contains four different sedum mixes that provide yellow and white flowering areas, and bluish-grey and red foliage areas.

The green roof contains four different sedum mixes that provide yellow and white flowering areas, and bluish-grey and red foliage areas.

The Dirksen Building green roof thriving.

Twelve months later, the green roof continues to thrive.

The pathways of the Dirksen Building green roof make a design with the U.S. Capitol Dome on the left, the Washington Monument on the right and a leaf in the bottom left corner.

Can you tell what design the pathways make? The U.S. Capitol Dome is on the left, the Washington Monument is on the right and a leaf is in the bottom left corner.

This story is also published in the Summer 2012 issue of AOC's Foundations & Perspectives.

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