Calvert Investments, a company that evaluates potential investment opportunities based on environmental and social factors, released a report this week that analyzed the green building practices of the ten largest publicly traded homebuilding companies in the US.

The study, which was made public on Tuesday, shows that the builders have made some ground in reducing the impact on the environment from their businesses.  Those strides vary widely from builder to builder, however, and the building industry, overall, still has a long way to go, the study said.

Homebuilding accounts for about 21 percent of the US' energy-related emissions of carbon dioxide , according to the report.  The study evaluated builders' land, building materials , ernergy, water, and climate change practices , relying on public data and some information obtained from the builders themselves.

Los Angeles-based KB Homes was ranked at the top by the study, surpassing its own record-high ranking from two years ago.  PulteGroup Inc. followed KB, with Meritage Homes Corp . coming in third.  The bottom three companies in the study were NVR Inc ., Ryland Group Corp ., and MDC Holdings Inc .

KB builds many homes with environmentally friendly features like low-flow water fixtures, insulation, and carpets and paint made with low volatile organic compounds .  The company constructed a home in Southern California earlier this year that uses batteries to store energy obtained from solar panels.  The builder has also been building a number of communities to meet guidelines concerning efficient energy and water use as set by the US Environmental Protection Agency .