Fordham Preparatory School's 3 story main builidng was completed in 1971 when energy was cheap. It contained no operable windows and had a terminal reheat air conditioning system (where air was cooled to a constant temperature and rewarmed as required at local mixing boxes). The system proved very expensive to operate as the 1970's energy crisis hit and was modified on an ad-hoc basis. Windows were single glazed and roof insulation was minimal.
A 4th floor was added in 2009. The addition featured operable windows and a significant upgrade to insulation. A greenhouse was part of hte addition and plant material is grown there and a layer of vegetation is gradually being added to create a green roof.
The result of the addition is that the building's volume was increased by almost 25% but the overall energy use was reduced. The building uses less energy today than it did before the addition.
This "carbon neutral" result is the goal of all our renovation work.