NEW YORK — Key players in real estate and construction misjudge the costs and benefits of “green” buildings by as much as 300%, creating a major barrier to more energy efficiency in the building sector, a new study by the World Business Council for Sustainable Development reports.

Respondents to a 1,400 person global survey estimated the additional cost of building green at 17% above conventional construction, more than triple the true cost difference of about 5%. At the same time, survey respondents put greenhouse gas emissions by buildings at 19% of world total, while the actual number of 40% is double this.

A study of actual projects in the U.S. showed that the cost premium did not exceed 10% for buildings rated by the U.S. Green Building Council’s Leadership in Energy and Environmental Design at the “platinum” level.

The findings are disclosed in a new report entitled, “Energy Efficiency in Buildings: Business Realities and Opportunities,” which summarizes the first phase of the WBCSD’s project. The project is co-chaired by French building materials manufacturer Lafarge and United Technologies Corp. The report is available at www.wbcsd.org.

“The global construction boom in the developing world has created a tremendous opportunity to build differently and dramatically decrease otherwise energy demands,” said United Technologies Corp. Chairman and Chief Executive George David. “Existing technologies combined with common sense design can increase energy efficiency by 35% and reduce heating costs by 80% for the average building in industrialized markets,” he said.

“The world is undergoing rapid transformation, with strong demographic and economic growth driving a move towards urbanization on an unprecedented scale,” said Bruno Lafont, chairman and chief executive officer of Lafarge.

Building professionals in the U.S. guesstimated that buildings contributed 12% of greenhouse gases, rather than the actual 40%. The average guess by building professionals in eight nations was 19%. “Building professionals” were defined as architects, specifiers, contractors, developers, commercial landlords and corporate tenants. The same group in the U.S. guessed that the cost premium for green buildings was 16%.

“Life cycle analysis shows that 80% to 85% of the total energy consumption and CO2 emissions of a building comes from occupancy through heating, cooling, ventilation and hot water use,” Lafont said.

The study also found that fewer than one in seven industry respondents has participated directly in a green building project. Involvement ranges from a high of 45% in Germany to 5% in India. About 20% of architects, engineers and developers have been involved in green building projects, compared to just 9% of owners and tenants.

In the U.S., 83% of building professionals said they were aware of green building, 43% had considered it, and 16% had been involved in a sustainable building project.

Buildings already represent approximately 40% of primary energy use globally and energy consumption in buildings is projected to rise substantially in the world’s most populous and fast growing countries such as China and India.

The study highlights opportunities to promote green building know how and technologies as the WBCSD pushes for zero net energy construction worldwide. Net zero energy use means buildings overall — although not every building — will generate as much energy as they consume.