Montclair residents and developers Bob Silver and Jay Schweppe for $2 million in April 2011, since the church no longer needed such a large space and was having difficulty keeping up with the maintenance.

Silver and Schweppe transformed the 23,000-square-foot structure into a dozen office suites and set aside 3,000 square feet for the congregation, which is also one of their renters.

The developers are inviting the community to next week's grand reopening of the reinvented building, which is being taxed for the first time in its 86-year history.

Silver would not say how much he and Schweppe invested to transform the structure, with the help of local contractor Jack Finn and architect Paul Sionas, into an environmentally "green" office building. But he did recall how much the congregation paid to have the church constructed back in the 1920s: a whopping $236,000.

"I paid a little more than that to renovate it," he joked.

Silver told The Montclair Times he is anticipating that Hillside Square will achieve silver LEED certification from the U.S. Green Building Council within a couple of weeks following its grand opening gala. The building has a highly efficient heating and air-conditioning system, is "super insulated," has well-sealed windows and other energy-saving features that make Hillside Square about 40 percent more energy efficient than it would have been had it been constructed in a traditional manner, Silver said.

The developers also tried to salvage and recycle as many elements of the old church as possible during the renovation process. The 632 pews formerly in the sanctuary were collected and shipped to Haiti, where they are to be used in nascent "tiny, storefront" churches, according to Silver. Workers from the oldest organ-restoring company in the nation, based in Paterson, collected the pipes from the old organ to use them as spare parts, he said.

Silver and Schweppe have also placed about 150 artifacts that had been kept by the church detailing its past — the original mortgage, building and landscaping plans, invoices for the pews and pipe organ, and other antiquated documents — on display on the second floor.

The hallways of the first floor will serve as gallery space for local artists, similar to other buildings that have been turned into offices by the same development team. These structures include BrassWorks on Grove at 105 Grove St., and Plymouth Street's Academy Square, the former home of the Kimberley School, the predecessor to the Montclair Kimberley Academy, and the Katharine Gibbs secretarial school.

Silver said he's proud of the project, since it keeps "this architecturally beautiful, granite building alive" and adds a new property to the tax rolls of Montclair, which, he noted, "is desperate for ratables."

Hillside Square is still valued at $1,803,400 based on last year's tax assessment, predating the renovations, according to the Montclair Tax Assessor's Office. The property owners' current annual tax bill is about $58,665. That amount is expected to increase an unknown amount as of next year, once the improvements are taken into account.

The building has also brought about 60 to 75 jobs to Montclair, as the township becomes "a destination for a creative class of businesses," Silver said.

"Creative space attracts creative tenants," Silver said of his renters, which include Trilogy Films, the biotech firm FluoroPharma Medical and FanBrandz, the firm that came up with a number of pro baseball logos.

"People realize they don't have to be in New York anymore because of technology," and if professionals ever need to get to the city, he noted, Montclair offers plenty of convenient public-transportation options.

Hundreds of people are expected to attend the grand opening, featuring music by Jazz House Kids, artwork by Catherine Kinkade, a ribbon cutting by the Township Council members, and refreshments. The event is scheduled for Friday, Oct. 26, from 6 to 9 p.m., at 8 Hillside Ave. in Montclair.