Paul and John Salib founded Castellan Real Estate Partners after finding individual substantial success with Red Stone Partners and Salomon Smith Barney, respectively. Under their direction, Castellan focuses on properties with long-term value. After buying properties, the company will often make significant energy-efficiency improvements such as installing dual-pane windows.

Also known as double-pane windows, dual-pane windows feature two sheets of glass fitted inside each frame, forming a double layer of protection from the outside elements. While air fills the space between these sheets in some basic types of dual-pane windows, higher-end dual-pane models are filled with argon gas for greater thermal efficiency.

Either way, dual-pane windows can make a big difference in terms of energy usage. For example, installing even basic dual-pane windows can reduce energy usage by nearly a quarter during the winter and up to 18 percent in the summer. Dual-pane windows also offer the benefit of reducing noise pollution--helpful in an urban environment--and eliminate the need for storm windows, which can be inefficient and a hassle to put on and take off each season.