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Congregants danced to Israeli music and rock `n' roll in the social hall — some wearing their hard hats even in a conga line. The oneg Shabbat room offered a quiet place to talk, plus "coffees and every kind of chocolate you could imagine," said Rabbi Melanie Aron.

Tacked to the walls were "Construction Zone" signs. Plastic hammers were strewn around like party favors.

"We have some fun memories of the construction," Aron said, recalling the transformation of the old 120-seat sanctuary, which was perennially overcrowded.

Three years ago, realizing that the congregation was quickly outgrowing its home, four congregants began fund-raising efforts. With $2.7 million in hand, the synagogue contracted Mark Schatz, architect of the Marin Jewish Community Center, to design its new space.

The 420-family congregation now boasts a hardwood-trimmed sanctuary that seats 450.

Dedicated in January, the synagogue has been "open for business" ever since. However, the Hard Hat Happening marked the first social event staged for the entire congregation.

Susan Lichte, a member almost since the congregation's inception 17 years ago and chairwoman of the event, called the $18-a-ticket party "a fun-raiser, not a fund-raiser.

"We went from the construction zone into the celebration zone," she said.

"It's such a thrill to see the growth and development of membership," she said. "We're thriving. And now we have a new building to celebrate different milestones and events and accommodate all of our members."

The high ceiling features a skylight. The padded seats, complete with a shelf for prayer books, are moveable, and link together to form both rows and circles.

"This allows us to have all sorts of different worship services: small circles for our alternative Shabbat minyan, and lines when we are having a bar or bat mitzvah celebration," Aron said.

In addition, the former sanctuary was renovated to double the number of classrooms to 18. It also houses offices for the rabbi, cantor, education director and support staff.

The new building isn't just a space expansion but is also "qualitatively much nicer. This used to be a bus depot and a [school district] administration building," Aron said of the Shannon Road location where Shir Hadash has resided since 1986.

Although the congregation is growing quickly, nearly doubling its size in seven years, Aron insists that Shir Hadash remains warm and inviting. She points to the simplicity of the sanctuary as "traditional of Europe: a lot of wood and space."

"This is not the Taj Mahal. We didn't want it to be."

Lichte agreed, adding, "Even without the building, this felt like a real community. The people made the synagogue before the building.

"But this beautiful building enhances what we have."