LEED certification is not reserved for new or improved buildings; the U.S. Green Building Council's Leadership in Energy & Environmental Design also has a commercial interiors category. LEED-CI certification looks at environmentally friendly office spaces.
"LEED for Commercial Interiors is the green benchmark for the tenant improvement market. It is the recognized system for certifying high-performance green interiors that are healthy, productive places to work; are less costly to operate and maintain; and have a reduced environmental footprint." Source: US Green Building Council
There are six different categories used when determining if a project will meet LEED-CI certification criteria: Sustainable Sites, Water Efficiency, Energy & Atmosphere, Materials & Resources, Indoor Environmental Quality and Innovation & Design Process.
While most of the categories have strict requirements, the Innovation & Design Process allows buildings to receive recognition for items not included in the other sections. The use of a LEED Accredited Professional on a project qualifies for one of five total points.
Points in the Innovation & Design Process category are awarded to projects that "substantially exceed a LEED performance credit such as energy performance or water efficiency." Additionally, interior spaces that "apply strategies or measures that are not covered by LEED such as acoustic performance, education of occupants, community development or lifecycle analysis of material choices" may receive points in this section. Source: LEED for Commercial Interiors
There is no better match for a LEED certified building than a LEED certified office interior. Office interiors that received LEED-CI certification can truly be called a green office.