The city planning commission yesterday backed the long-awaited redevelopment of the former South Hills High School on Mount Washington, a project that has been some three years in the making.

At the same time, members heard a pitch by the Penguins to add a fifth level to a 500-space parking garage at the new arena to accommodate guests who will be staying at a hotel to be built next to it.

In a unanimous vote, members approved plans to convert the South Hills High School building, which has been vacant for more than 20 years, into housing for seniors -- 106 apartments in all.

A.M. Rodriguez Associates, which was selected by the city Urban Redevelopment Authority in 2005 to develop the site, also is planning a 7,500-square-foot YMCA and a 4,500-square-foot early childhood development center on the ground floor.

There also will be at least 123 parking spaces to accommodate residents and visitors.

"I think it's wonderful that a building that has been empty so long and a nice building is going to be utilized," commission member Mary Lou Simon said.

Of the 106 apartments, 84 will be for seniors with low and moderate incomes and another 22 will be at market rate. The project is expected to cost $25 million, funded through low-income housing tax credits and loans.

Although an auditorium and a shop wing will be demolished as part of the conversion, the main U-shaped high school building will remain intact. The developer will be seeking an environmentally friendly Leadership in Energy and Environmental Design, or LEED, certification for the project.

A.M. Rodriguez hopes to begin construction in March and have the first units ready for occupancy in June 2010.

The Penguins, meanwhile, are seeking the additional level of parking, enough to accommodate about 145 vehicles, as part of the proposed 132- to 142-room hotel development, to be built on Centre Avenue in the Hill District, adjacent to the new arena.

Howard Graves, president of Graves Architects Inc., said the change will add a fifth level to the garage, but shouldn't affect views along Centre. He said nearly all of the garage will be blocked from sight by the seven-story hotel, which is expected to open in 2010 in conjunction with the $290 million arena.

At a briefing, commission member Paul Dick urged Mr. Graves to discuss the proposed hotel development with nearby Crawford Square residents. Mr. Dick said the hotel would be different than the arena itself in that it would operate 24 hours a day, seven days a week.

Also yesterday, the commission approved:

• Plans for a seven-story office building at Ruskin Avenue and Bayard Street in Oakland. The $14 million project is a scaled-down version of another proposed several years ago. It will feature general and some medical office space. Developer Elmhurst Co. LP hopes to begin construction in March in anticipation of a September 2010 completion.