It is necessary to build structural elements that are economical and that in turn support the loads to which they are subjected.On the other hand, it is important to control CO2 emissions in construction processes.The excess of this gas is the main cause of global warming by the greenhouse effect.In this context, this work presents a sensitivity analysis to assess the impact of different design parameters on the optimization of cost and CO2 emission of reinforced concrete footings.The design parameters are applied load, soil elastic modulus, Poisson ratio, angle of internal friction, factor of safety and allowable settlement.For this, the metaheuristic called Modified Simulated Annealing Algorithm is used to obtain the optimal designs.