As redevelopment sites go, 116 E. Hennepin Av. in Minneapolis was a prize. The nearly half-block parcel housed four old storefront buildings, including the popular Nye’s Polonaise Room, in a bustling neighborhood just a block from the leafy banks of the Mississippi River.

From a construction standpoint, the sloped, irregular-shaped site was a major league headache.

Two of the four buildings had historic protection and couldn’t be significantly altered; the oldest church in the city was right next door, and the buildings sat atop a deep deposit of bedrock that made blasting a hole deep enough to build a standard underground parking garage financially and logistically impractical.

Those site challenges and the complexity of stitching together the old and new buildings quickly made this the most complicated that Katie Anthony, a project manager for Schafer Richardson, had ever tackled.

“The methods for getting rid of that bedrock were not palatable,” said Anthony. “There were multiple challenges.”

Schafer Richardson, a seasoned Minneapolis-based developer, originally wanted to build a nearly 30-story concrete tower atop several levels of above-ground parking.

For a variety of reasons, that plan was scuttled in favor of a stick-built, low-rise apartment building that would replace two of the buildings and wrap around and sit atop the remaining two buildings.

Dramatically shrinking the height of the building solved several problems, but created one that was nearly insurmountable: A multilevel, above-ground parking garage was no longer feasible. Neither was forgoing a heated parking garage with enough spaces for every unit.

With population density on the rise in that part of the city, parking is highly coveted. In some condo buildings in the area, spaces fetch upward of $50,000, so not including sufficient parking would put the 67-unit building at a major competitive disadvantage.

So Schafer Richardson hired Denver-based Harding Steel to build what’s being called the first residential semi-automated, mechanical car stacking system in the Midwest.

The company’s CARMATRIX is essentially a Rubik’s Cube for cars.

The system is a grid of steel frames that supports a series of stacked galvanized steel platforms that move up and down and side to side. A metal gate closes behind the cars after they enter or leave the platform.

For each grouping of platforms, a vacant space at grade level enables the upper and lower platforms to move around to access a vehicle when it’s called by its owner using a portable remote control.

Unlike garage elevators that simply lift vehicles from one level to the next, and typical car storage systems that are operated by professional car parkers, the CARMATRIX enables residents to have an assigned space and park their own cars, eliminating the need for an attendant or a valet parker, Anthony said. The entire process takes just a couple minutes.

Because the M on Hennepin site was heavily sloped, the company was able to build a second traditional at-grade parking garage, giving residents another option. There are 26 spaces in the CARMATRIX and 37 in the traditional garage.

Though there was a steep learning curve for the building manager and the first residents, the CARMATRIX hasn’t been an obstacle to renting units. Since the building opened late least year, it’s been fully occupied.

In addition to the complexities of the site, designing the building around the CARMATRIX wasn’t easy. Anthony credited ESG Architects and Frana Cos. with figuring out how to tie the metal structure to the post-tension concrete structure.

A team from Twin Cities-based Rebel Electric flew to Seattle to inspect another system before installing the one at the M on Hennepin; they’ve become a local expert on the system, Anthony said.

Such systems are well-suited for cities where land prices are soaring and developable space is at a premium.

Ryan Myers, Harding Steel vice president, said that demand for its CARMATRIX and Combilift products, which are both based on the “puzzle” concept, has been on the rise.

The company is working with a developer in Hudson, Wis., but that project is still in the planning stages.

He said the system costs $14,000 to $16,000 per car, depending on options and the number of stalls.

Myers said developers in many second-tier and even some small but fast-growing cities, including Portland, Maine and Portland, Ore., are considering the option.

“It’s a way to optimize parking and development design and not be forced into hiring a valet operator to manage parking,” said Myers.