Allegheny County Executive Dan Onorato was on one of the top floors of the Grant Building a few months ago when he looked below and noticed the expansive roof of the nearby County Office Building on Forbes Avenue.

"I looked over and the idea came to me: We can use this roof as green space," he recalled yesterday as he unveiled plans to create a plant garden on the roof of the building at 542 Forbes Ave., and a water garden in the courtyard of the county courthouse.

The county, he said, plans to use half of the roof of the County Office Building for a green roof. The 8,400-square-foot area will be covered with waterproof fabric, soil and plants native to Allegheny County.

The green roof is expected to increase the building's insulation, thus cutting down on heating and cooling costs. The roof garden is expected to absorb much of the storm water runoff that would otherwise end up in the storm sewers.

The unconverted half of the roof will be left open and equipment will be installed to measure the difference in storm water runoff between the two halves.

The Penn State Cooperative Extension in Allegheny County and 3 Rivers Wet Weather have partnered with the county. The Penn State group will use the information to demonstrate the benefits of green roofs to residents and businesses in the region.

In the courthouse courtyard, four existing planters will be retrofitted and converted into rain gardens. Four downspouts that currently drain into the city's sewer system will be diverted into the planting beds.

As part of the project, the courtyard will be re-leveled and the existing brick will be cleaned and repainted. The project in the courtyard will be done by county public works employees and craftsmen, and construction is scheduled to begin later this month.

County officials said they don't yet know how much the entire project will cost because they have not received bids for installation of the roof garden on the County Office Building. That project is scheduled for completion by year's end.

Calling both projects a significant step toward making Allegheny one of the "greenest counties" in county government operations, Mr. Onorato said the projects are key components of the county's development plan known as Allegheny Places.

"These projects will save energy, reduce storm water runoff, and cut down on the amount of pollution reaching our rivers," he added.

However, Mr. Onorato isn't the only one looking to put a green roof on a public building Downtown.

The city's Urban Redevelopment Authority board plans to vote tomorrow on a grant request to the Pennsylvania Infrastructure Investment Authority for up to $300,000 to install a green roof on the John P. Robin Civic Building at 200 Ross St. The cost of the project is estimated at $257,400.

In addition to the environmental benefits, the URA said the roof would "serve as an educational tool to building visitors as well as a symbol of the city's commitment to sustainable development."