In my Indianapolis Business Journal column listing 10 things Indianapolis could do to make our already thriving downtown an even better place to live, the second item was: Have the guts (and the money) to build more than five stories.

Downtown Indianapolis has a few notable existing and planned high-rise places to live, but many of the new residential projects are four stories. If we’re going to get to sustainable urban density, we need to mix in more mid-rise places to live.

Sustainable urban density is what it takes to support a healthy base of restaurants and retail. While our Mass Ave and Fountain Square restaurants are busy from 6 to 8 p.m., similar restaurants in Chicago would still be crowded until 10 p.m. Our sidewalks and retail stores might be bustling on a Saturday afternoon, but many are empty other parts of the day and days of the week. Right now it’s taking longer to fill the first-floor retail and restaurant spaces in new mixed-use buildings than it is to rent or sell the residential units above them. We need to correct that imbalance with more buildings that have more stories of residential above the retail.

Sustainable urban density also keeps downtown walkable, so you can easily walk or bike to work. If there are too many four-story buildings, they sprawl out over more land to meet the demand for downtown living. That’s what spread the city out before, and we should try to avoid that in this new wave of urban living.

Granted, it is more expensive to build structures that are more than four stories. Once a structure is designed to be above a 78-foot height, building code requires a steel structure, and the elevators must be electric powered, not hydraulic.

But taller buildings also give building owners better value for the footprint of the land. To make buildings economically sustainable, the owner needs a certain number of units to sell or rent. Rents can be more reasonable when there are more units per building, and downtown needs more affordable units for young professionals.

Do we want all high-rises downtown? No, our city is more visually interesting and inviting with a mix of building heights.

Good design is important and enhances the economics as we consider what makes downtown living work.