By Andria Cheng 

Fair Trade coffee and chocolate have become commonplace. Get ready for Fair Trade fashion and décor.

Two years after a garment-factory collapse in Bangladesh killed more than 1,100 people and put a harsh spotlight on fashion-industry working conditions, Fair Trade apparel is gaining ground.

The volume of apparel and home goods sold as Fair Trade Certified has grown rapidly in the past two years, according to the nonprofit certification group Fair Trade USA, which in 2012 introduced more than 334 compliance criteria for textile factories.

Fair Trade USA's apparel certification now appears on 20 brands, up from just a handful before the Rana Plaza factory collapse in Bangladesh. Patagonia, Williams-Sonoma Inc.'s West Elm unit and Bed Bath & Beyond Inc. are among retailers that began selling Fair Trade Certified apparel or home furnishings in the past two years, according to Fair Trade USA.

The number of factories certified by Fair Trade USA is expected to increase to at least 25, in countries from India to Colombia, by the end of 2015, up from fewer than five in 2012.

A range of factors are measured by the group before a factory is labeled Fair Trade Certified--which is a trademarked designation. Those include a factory's environmental impact, its overall working conditions and the rights afforded workers. As a baseline, workers must be guaranteed local minimum wages. Brands also are required to make additional payments, based on how much they buy from factories, directly to workers in what's called a Fair Trade Premium.

The total cost to the brands, including third-party factory auditing, worker training and the Fair Trade Premium, is, on average, about 1% to 5% of what brands pay to factories, said Maya Spaull, director of Fair Trade USA's apparel and home goods category.

Fair Trade USA, according to a West Elm representative, is the only group certifying production facilities for home and apparel manufacturers involved in large-scale production. "Traditionally, certification has been limited to raw materials or outputs," said West Elm spokeswoman Abigail Jacobs.

Fair Trade USA--founded in 1998 to certify coffee production--now certifies in 30 categories, ranging from furnishings to flowers to spices to lip balms, as well as clothing.

Certified ethical apparel and home goods "need to be available to a wider mass-market audience" to "effect true positive change," just as organic food choices have gone mainstream, said Marci Zaroff, founder and CEO of Under the Canopy, a fashion brand that works with Fair Trade USA.

Under the Canopy's Fair Trade Certified line of bedding, introduced for back-to-school season at Bed Bath & Beyond last year, sold out immediately, according to Ms. Zaroff. "Millennials are seeking authenticity and transparency," she said. They are the ones "driving the rapidly growing movement for sustainable and ethical fashion."

Under the Canopy has added more Fair Trade collections at Bed Bath & Beyond, including lines of organic cotton kimono robes and throws, which it also sells through Amazon.com and Wayfair.com.

West Elm is expanding the six Fair Trade Certified rug offerings introduced during the 2014 holiday season to 30 rug lines and 13 textile collections this fall, said Ms. Jacobs, adding that the broadening of its certified offerings "speaks to the customer's interest" and "commitment to consciousness."

Whole Foods Market Inc. began carrying Fair Trade Certified T-shirts made by Pact Apparel in the spring of 2014. The shirts, which cost $15, are one of Whole Foods' best-selling basic apparel lines, the company said.

At yoga and outdoor-apparel brand Prana, which was acquired by Columbia Sportswear last year, the single Fair Trade Certified T-shirt introduced in 2010 led the way to nearly 100 items, including dresses, skirts and men's shirts, said Nicole Bassett, the brand's director of sustainability. In fact, Fair Trade products now represent about 15% of the overall assortment at Prana, which has approached some existing suppliers to help them get certified, Ms. Bassett said.