Boston-based William Rawn Associates (WRA), with the highest revenue-per-employee figure of any ranked firm this year, and a 9 percent increase in billings in 2015, has a financial position that would turn most architects green with envy. You might assume this is because the firm has a full-time rainmaker on staff or a managing director with an MBA—in fact, it’s just the opposite. WRA prospers by letting architects be architects and seeing that they don’t get overextended.

The firm abides by a hard rule, says founding principal William Rawn, FAIA. “We limit ourselves to six projects in design at any given time. If we’re good at selecting six projects that are about getting buildings built, and not trying to be all things to all people, [it] gives us a real focus and a rigor.”

Winsor School Lubin O'Donnell Center in Boston
Robert Benson Photography Winsor School Lubin O'Donnell Center in Boston

A deep expertise in higher-education, performing-arts, and civic buildings has become the firm’s calling card. Projects have grown in scope and budget, but not number, which means that staffing levels don’t follow the wild peaks and troughs of boom-and-bust cycles. “We’ve been able to grow and have our practice reach a sweet spot somewhere in the mid-30s to mid-40s [in size] and be able to have an impact,” says Cliff Gayley, FAIA, a principal who has been at the firm for 27 years.

In the last couple of years, WRA has innovated on one of its signature building types, the campus performing-arts facility. At the Winsor School in Boston and at Duke University, the architects designed day-lit, multipurpose buildings that give an unusual prominence to the back-of-house spaces—where most of the learning happens. Pushing the envelope on a familiar typology in this way helps keep the work fresh. It’s also opened up new avenues for the firm. WRA is now tackling a healthcare project for the Cleveland Clinic and a net-zero-energy public middle school in Cambridge, Mass.

Does branching out mean the end of the six-project rule? No, Gayley says. “I think that’s so central to how we’re able to manage quality and projects from a design point of view, and delivery of service with our clients.”

“People talk about growth as being an essential component of business,” notes principal Douglas Johnston, FAIA. “In our model, growth is in changing the scale and complexity and consequence of the projects, and the project types, rather than changing the number of projects we take on or the number of employees we would have.”

It’s a starkly different conception of growth from the world-conquering model of a Walmart or Starbucks (or a global design firm, for that matter). But it works. “We don’t have to spend huge amounts of our time out there, rainmaking,” Rawn says. “We want to be architects.”

Check out the list to find out which firms rose to the top,and discover who made the cut in each of the three categories: business, sustainability, and design.

Read more about top firms ZGF (overall and sustainability) and Marlon Blackwell Architects (design).

Also check out some key data submitted by firms and our methodology.