Israel Idonije is hoping to turn a few floors in a Loop office building into home base for Chicago's nonprofit sector.

Expanding on an idea he is pursuing on the Near South Side, the former Chicago Bears defensive end has leased 45,000 square feet at 200 W. Madison St. for a venue meant to bring together charities, foundations and other philanthropic ventures around the city.

Framing it as a "philanthropy innovation center" set to open in March, Idonije has subleased all of the available private offices to a series of charitable funds and foundations in what he has dubbed the FBRK (pronounced "fabric") Impact House.

The goal: Create a place to unite what Idonije deems a fragmented local philanthropic landscape to help connect big donors to organizations with big social impact goals. Think Chicago tech incubator 1871, but targeting nonprofits.

The space "will stand as the place in our city where anyone can come to find out what's going on in a sector of impact that's important to them," Idonije said. "We want to know who's giving to great work, who's actually doing the work. . . .We want to do an impact audit across the entire city."

The idea spun out of a project Idonije and former Bears teammate Julius Peppers have been developing on Motor Row, where a venture of theirs paid $10 million last year for the former Hudson Motor Building at 2222 S. Michigan Ave. They plan to turn that five-story building into FBRK, a co-working and member club space designed to foster collaboration in specific industry sectors including tech, nonprofits, sports and art. They've since added plans for a 109-room boutique hotel to that project, which Idonije aims to open in 2021.

Idonije, who has been involved in the nonprofit sector through his own foundation, pivoted to open the Impact House to meet what he sees as an imminent need to bring philanthropic groups together in the city.

"There are some incredible people and organizations in the city that are doing meaningful work," he said. "How can we, in a meaningful way, connect (them) and make sure stuff being done out there is efficient?"

In addition to private offices, which are leased to grant-maker groups including the Field Foundation of Illinois and Woods Fund Chicago and nonprofit association Forefront, the Impact House will include 15 conference rooms and four "work lounges" available for use by members that would pay $3,000 per year to use the space.

Idonije stressed that the space is not akin to co-working, which has proliferated in the office market as companies gravitate to such low-risk workspace they can lease by the month. Prospective members will apply for a slot in the Impact House that will be evaluated by a committee.

Idonije might find some takers. Finding offices downtown is getting harder for nonprofit organizations, which often lease offices in more budget-friendly, lower-quality buildings. Those types of functionally obsolete buildings are disappearing in the city as real estate investors have converted many to other uses or turned them into trendy creative offices that command higher rents today than in the past. The amount of such "Class C" space across the East, Central and West Loop dropped by 26 percent between 2009 and 2019 to 14.3 million square feet, according to real estate brokerage CBRE.

"We can bring in the family foundation that has two people and doesn't have space. . . .That group can come in and have amazing, innovative space for a fraction of what they pay if they take down the whole space by themselves," Idonije said.

Idonije, who spent most of his 11-year NFL career with the Bears, said his venture has leased space for the venue for a term "beyond five years" and that foundations are subleasing office space on three- to five-year terms.

The Impact House will span three floors in the 45-story building and will include an Italian-themed restaurant operated by the Chicago-based Fifty/50 Restaurant Group that will be open to the public.

The lease boosts the tenant roster at 200 W. Madison St., which is owned by a venture of Bethesda, Md.-based investment fund Multi-Employer Property Trust and Toronto-based real estate firm Bentall GreenOak. The tower is around 93 percent leased, according to real estate information company CoStar Group. Its largest tenant is law firm Barack Ferrazzano Kirschbaum & Nagelberg.

Brokers Larry Serota, Cece Conway and Holly Bailey of real estate services firm Transwestern represented the Idonije venture in leasing the FBRK Impact House space.