Within the rapidly growing fast-casual sector of America’s restaurants, one subcategory is rising far above the competition: build-your-own fast-casual concepts. In 2014, restaurants with a build-your-own format, which moves consumers down the make line and allows them to customize their meals, increased sales twice as fast as made-to-order fast-casual brands. The former reported a collective annual-sales gain of approximately 22 percent, compared with an 11 percent increase for the latter, according to data collected for Technomic’s Top 500 Chain Restaurant Report.

"Consumers certainly like the freshness, food quality and prices at made-to-order fast-casual brands, but there is something about the build-your-own format that they prefer significantly," said Darren Tristano, executive vice president of Technomic. "More customers, especially Millennials, see the personalization and engagement that come in a build-your-own menu offering as the greatest differentiator in dining out. These trends are likely to lead fast casual's growth for years to come."

The fast-casual industry grew its annual sales approximately 13 percent last year to $39 billion. While that is a relatively small share of the total restaurant industry's $466 billion in annual sales in 2014, fast casual's growth rate dwarfed the total industry's annual increase of 3.8 percent. Fast-casual brands also increased their unit count 9 percent in 2014, far faster than the 1.3 percent gain in new locations for the total restaurant industry.

All menu categories in the report showed sales and unit growth, but several clusters showed interesting developments:

Like the bakery-cafe segment, which grew sales 6 percent and locations 5 percent, the Mexican category is one of fast casual's most developed and mature clusters, yet it posted gains of about 18 percent in sales and 6 percent in locations. Chipotle Mexican Grill continued to lead the way with a nearly 28 percent sales increase in 2014. While still expanding and taking market share from quick-service brands, fast-casual Mexican chains and bakery-cafes are likely to grow slower in the coming years than specialty concepts in emerging segments.

The pizza category, led by fast-growing chains like Blaze Pizza, had the largest annual-sales gain of 22 percent in 2014. Store count growth, which increased 27 percent, is driving much of fast-casual pizza's sales performance, helping those brands steal market share at lunch and dinner. As new players enter the segment, expect several more years of rapid growth for fast-casual pizza.

The specialty cluster, which comprises categories like salad, Mediterranean and barbecue, posted an approximate 20 percent increase in sales and a 13 percent gain in units.