coastal smart growth
Low Impact Development Case Study
City of Boston - City Hall Green Roof
Highlight: Boston installed a green roof — of 150 modular pre-grown gardens—on the eighth and
ninth floor terraces of City Hall to help capture and treat stormwater runoff at the source.
Why Low Impact Development (LID)?
Roofs cover a significant portion of the urban landscape and generate
large volumes of stormwater runoff. When it rains, this stormwater
flows through the municipality’s drainage infrastructure into natural
waterways, having the potential to create irreversible damage to local
ecosystems via erosion and water-borne pollution.
What LID Practice Was Applied?
Green roofs are one method of reducing stormwater runoff. Initially
designed to provide insulation in cold climates such as Iceland and
Scandinavia, green roofs have recently been developed to harness water
retention capabilities to reduce runoff in urban areas. By using a layer
of vegetation instead of traditional impervious roofing systems, a large
amount of rainfall can be captured, retained, and filtered at the
The city of Boston, prompted by the momentum to be “green” for the
Democratic National Convention held in Boston in 2004, and as part
of the recommendations provided by the Green Building Task Force,
recently installed a green roof—150 modular pre-grown gardens—on
the eighth and ninth floor terraces of City Hall. The modular gardens,
also known as “green grid” modules, include 12 varieties of sedum, a
species commonly used for rooftops because they have high water retention capability, an ability to filter
pollution, and are drought tolerant. The plants were also selected for their shallow root systems, regenerative
qualities, and hardiness to the elements of sun, frost, and wind.
What Was the Project Scope, Timeline and Budget?
The modular garden is the pilot project for what Boston hopes will be the green roofing of the entire City
Hall roof. Due to its high visibility on the eighth and ninth floors, the project wi