Sarah Heinz House is one of those venerable Pittsburgh institutions that thousands of people drive by every day and never notice, which is probably a good thing. Take your eyes off the road and you might get creamed.

It's hard to imagine a more inauspicious location for a Boys & Girls Club than at the intersection of the 16th Street Bridge and a tangle of ramps where East Ohio Street becomes Route 28.

But as is often the case when modern highways cut through historic neighborhoods, there's a secret world in the streets and buildings so quickly passed by. In this case, it lies within a 94-year-old former settlement house where generations of children have learned to swim and dance, play basketball, become leaders, make music and art and friends, and been enriched in countless ways. And for some of the children in recent months, green design has become not only a way to build, but a way of life.

For 17 Sarah Heinz House members between the ages of 12 and 15, the new 30,000-square-foot addition to the club has been a case study in sustainable building from the ground up.

"We talked about a lot of green facts but then we would see how the green facts are applied in the green building," said 15-year-old Matt McKee of Shaler a few days ago as the group sat around one of the big oak tables in the lobby of the original building.

"It's not all facts; that sounds boring," said Marritta Gillcrease, 13, of Observatory Hill.

Matt agrees: "It's the principle of how things work when they're green."

For 18 months beginning in January 2006, Matt and Marritta and 15 other Hard-Hat Kids, as they're called, visited the job site weekly in hard hats, safety glasses and thick-soled boots. They talked with architects and contractors and learned how a building is designed and put together, and what makes a building friendly to the environment.

"One of the things we were trying to do with the new building is use a lot less energy," Matt said in the lobby of the new building, at an open house in March for family members. "Seventy-five percent of this building that's in regular use will be day-lit, so we'll spend a lot less on electricity costs."

In the past few months they've given tours to almost 1,000 people. This weekend, the Hard-Hats will be on the job again, at tomorrow's free Community Day celebration, when for the first time the new building opens its doors to the public. They'll offer tours after the 11 a.m. ribbon cutting; visitors also are invited to swim in the new pool and try out its aquatic climbing wall, do art and craft projects, play games, listen to live music and enjoy a cookout.

It will mark Sarah Heinz House's transition from a Boys & Girls Club to something closer to its settlement house roots.

With the addition, "the idea was to make it a place the community could call home," said board President John Bonassi.

The pool, with walls of windows on two sides, is the first thing you encounter when you enter the new lobby, dubbed the Grand Hall.

"One of the goals was to see the energy of the runners in the pool when you come in," architect Terry Oden of Rothschild Doyno Architects said at the family opening. "You're drawn to the glass."

That glass does something else, too: It allows you to see right through the new building, to the houses on the opposite side of East Ohio Street.

"Visually we're reconnecting to the community," architect Ken Doyno told the families.

Rothschild Doyno Architects of Regent Square collaborated with William McDonough + Partners of Charlottesville, Va., which was responsible for shaping the green aspects of the building. The architects are applying for a Silver LEED rating from the U.S. Green Building Council.

In a report written for LEED certification, Hard-Hat Rachel Volkman, 14, of Observatory Hill, said she learned about "nature cycles, the environment, green construction and preservation of our earth, but also how to work with people of all ages."

The club's environmental educator, Suzanne Matoney, who designed the Hard-Hat program, emphasized nature as the original recycler.

She said the welcoming attitude of Dan Dean, project manager for Dick Corp., the builder, made all the difference. He provided the hard hats, safety glasses and safety training that allowed Ms. Matoney and the children on the job site.

In addition to the pool, the new building houses a fitness center, dance studio, gymnasium and black-and-gold locker rooms. The $11.4 million building program also funded improvements to the existing building, erected by Howard Heinz in 1913 in memory of his mother, Sarah, whose portrait hangs above the mantel in its lobby. The Heinz Endowments, which provided $5.5 million toward the cost, initiated the green emphasis.

Although the building is finished, some aspects are not, including signage, fencing and landscaping, which will include a vegetable garden. The Hard-Hat program will continue indefinitely, with members doing community outreach about green design.

They've also learned to be better stewards of the environment at home. It's something Ms. Matoney taught them about "The Power of One," the mantra printed on the Hard-Hats' T-shirts: "One thought, one idea, one change, one decision, one earth, one chance, one another."

For Sam Greco, 13, of Shaler, being a Hard-Hat was both a good and bad experience. "Bad knowing how much damage has been done to the environment, good knowing that we can change it."

"When I brush my teeth," said James Pace, 12, of Squirrel Hill, "I turn off the faucet."