Figuring out how the act of home building affects the planet has always been a somewhat vague science, until now. Today, builders, developers, and architects can gauge the eco-friendliness of projects that are on the boards or underway using an online "construction carbon calculator" that quantifies the role of construction processes in the global warming equation.

Whereas other metrics tend to focus on greenhouse emissions produced during the lifespan of a completed building, www.buildcarbonneutral.org calculates the amount of CO2 produced specifically during the construction phase. Created by Mithun, a Seattle-based architecture and planning firm specializing in sustainable design, in partnership with the Lady Bird Johnson Wildflower Center at University of Texas, the tool synthesizes factors such as habitat disturbance or protection, landscape installation or restoration, building size, materials, and processes. It is applicable to a range of project types and settings, from urban contexts without vegetation to large-scale greenfield developments.

Using square footage measurements, the calculator prompts users to input variables such as a building's size, number of floors, and structural frame material, as well as the project's eco-region and the amount and type of indigenous landscape removed or added.

Sean Cryan, a LEED-accredited designer at Mithun, says the web application is intended as a process tool to help builders calculate the carbon footprint of a given set of project specs, and then figure out ways to reduce waste, renew energy, and offset carbon output by making adjustments to the pro forma. "We've introduced BuildCarbonNeutral as a starting place. Once you have a number, you can begin to take action," he says. "We hope that more complex forms will develop to include carbon offset recommendations in addition to carbon release measurements."

Buildings account for approximately 48 percent of greenhouse gas emissions in the U.S., according to the Environmental and Energy Institute.

Learn more about markets featured in this article: Seattle, WA.