PHILADELPHIA Looking to enhance its presence on a burgeoning stretch of North Broad Street, Congregation Rodeph Shalom plans a major expansion of its historic synagogue with its Romanesque columns and colorful mosaic front.

Michael Hauptman, an architect and member of the congregation's board of directors, said that the current building at Broad and Green Streets, which he described as "Art Deco with Middle Eastern designs," will get a new addition on its south side.

The $15 million expansion, which was approved by the board last month, will also face Broad and be built on what is now a portion of the synagogue's fenced-in parking lot. Construction is to begin later this month and will take about 17 months, Hauptman said.

He said Rodeph Shalom, which was established in 1795, is the oldest Ashkenazi congregation in the Western Hemisphere and its temple the only Reform synagogue near Center City.

Hauptman said the building was constructed in 1928. It replaced the synagogue's previous building, which was designed by Frank Furness.

Congregation president Dena Herrin said the expansion project follows $10 million in renovations to the current building over the last few years. She said the expansion and renovations were needed to make the building more attractive and accessible.

"When you walk around this building, it's not very welcoming," Herrin said. "Its hard to know where to enter. There are no windows.

"This building is very unfriendly to anybody with even the slightest mobility challenge."

The 18,500-square-foot addition, designed by KieranTimberlake architecture firm, will include new classrooms and meeting space, officials said.

"We have been bursting at the seams with new growth," Herrin said. "Our school has doubled in size in the last five years. We have many new members."

She said that the congregation had about 3,000 individual members and that membership had increased 25 percent since 2008.

"We're meeting a need in the Jewish community that isn't being met elsewhere," Herrin said.

She said that the congregation had many interfaith families and that non-Jewish members of those families were full members of the synagogue.

Herrin said there were several synagogues on North Broad Street in the 1950s and '60s before a mass migration to the suburbs.

"Everyone else left. We were the only ones who stayed," Herrin said. "We made a very difficult decision to stay on North Broad Street when everyone else left because we have always been very very committed to this neighborhood."

The current building contains a renovated ornate domed sanctuary with stained-glass windows and a skylight; a religious school for pre-kindergarten through grade 12; and a Jewish art museum.

The synagogue also has an early-learning center, housed next to the synagogue in a former car dealership.

Herrin said Rodeph Shalom has supported progressive causes, adding: "Our board passed a resolution several years ago in support of gay marriage."

She said community groups also used the synagogue.

"We have a lot of interfaith work that we're doing outside, as well as a lot of outreach in the Jewish community," Herrin said.