An environmentally friendly 2 comma 400-square-foot green home (99% air tight) costs about 6% more to construct than a same-sized conventional home. most green homes can save 17% per year on energy expenses to heat and cool the living space. for a $249 comma 000 conventional home with a heating and cooling bill of $3 comma 500 per year, how much would have to be saved in energy expenses per year to justify this home (i. e., b-c ratio greater than or equal to one)? the discount rate is 12% per year, and the expected life of the home is 24 years.