A black and yellow butterfly landed for a moment on one of the white flowers transplanted on the roof of the County Office Building.
Darla Cravotta was delighted to see the insect taking advantage of the new garden under construction 70 feet above Forbes Avenue, Downtown.
"It's like a scene from 'Avatar,' " she said.
Ms. Cravotta, who is special projects coordinator for Allegheny County Executive Dan Onorato, was one of the tour leaders Tuesday on a visit to the first "green roof" being installed on a government building in southwestern Pennsylvania.
The county is following the lead of the University of Pittsburgh, Carnegie Mellon University and several public and private property owners who have done similar projects.
Landscape workers were planting a variety of ground-hugging evergreens, succulents, perennials and annuals on top of the 80-year-old office building. Eric French, president of Eisler Landscaping, said the plants and the lightweight soil in which they are growing will help keep the structure cooler, hold and clean storm water and extend the life of the roof.
The new green oasis also will improve the visual aesthetics for cubicle dwellers in the nearby U.S. Steel Tower, One Mellon Center and other Downtown skyscrapers, Ms. Cravotta said.
The $621,000 roof project is the latest element in Allegheny County's "Green Initiative." It is being paid for with federal stimulus funds.
The garden covers about 8,400 square feet on half of the county building's flat roof. Instruments to measure inside and outside temperatures, humidity and water retention will provide data for comparing cooling and heating costs on the planted and unplanted sides.
That information will be used in discussions with Downtown building owners and landscape architects in hopes of persuading them to convert the tops of their properties into energy-saving gardens.
There are about 1,500 acres of roofs in the Golden Triangle, according to Janie French, director of green infrastructure programs for the Pennsylvania Environmental Council. She estimated that roofs suitable for gardens total about 24,000 acres across the county.
Ms. French, who served as a consultant on the county's green roof, is not related to Mr. French, the landscaper.
The top of the County Office Building has been landscaped with hidden foam supports to create a pattern of valleys and hills similar to the topography at Pittsburgh's Point.
That makes the county's first green roof an ideal tool for demonstrating the different kinds of plants, drainage systems and growing materials that can be used in such projects, Ms. French said.
Len Barcousky: email@example.com or 412-263-1159.