This story was originally published in Builder.

In the 20+ years since the U.S. Green Building Council first developed its Leadership in Energy and Environmental Design (LEED) certification, the nation’s LEED-certified construction volume has grown to comprise about 40% of green construction’s contribution to the economy, according to the USGBC’s Leticia McCadden. By 2018, LEED-certified construction is expected to contribute nearly $30 million to the nation’s GDP – a number that may only grow with time, as the USGBC certifies over 2.2 million new square feet of LEED space each day.

LEED is far from the only green building practice or certification out there, either – and according to a 2016 study by Dodge Data & Analytics, green building practices double across the globe every three years.

Out of 5.77 billion completed square feet across 165 countries, over 1.3 billion completed square feet of LEED-certified space exists in the US across 38,353 projects, commercial and residential alike. That’s enough space to cover almost all of Staten Island, or about 23,000 football fields.