This is the best software I have found to analyze both new construction and retrofit improvements for optimizing energy efficiency improvements decisions for residences. It is free software developed with our tax dollars by National Renewable Energy Laboratories.

Which retrofit will give you the most bang for your buck? This is the software package to answer that question and take the design process from energy-intensive construction to an elegant whole-house net zero design solution and any point in between. for example you might wonder how much energy can you save by designing a house with ducts in the conditioned space versus in an unconditioned attic. This allows you to compare alternatives such as this, as well as among different glazing assemblies, types and amounts of insulation, appliance types, etc.

From their website:
“The BEopt™ (Building Energy Optimization) software provides capabilities to evaluate residential building designs and identify cost-optimal efficiency packages at various levels of whole-house energy savings along the path to zero net energy. BEopt can be used to analyze both new construction and existing home retrofits, through evaluation of single building designs, parametric sweeps, and cost-based optimizations. BEopt provides detailed simulation-based analysis based on specific house characteristics, such as size, architecture, occupancy, vintage, location, and utility rates. Discrete envelope and equipment options, reflecting realistic construction materials and practices, are evaluated.”