The objective of this project was to compare energy consumption and incremental building costs when single-family residential homes are built and operated according to different codes, namely the 2000 International Energy Conservation Code and the 1992 Model Energy Code or lesser. The lack of quantitative information such as energy savings and incremental building costs has made it difficult to mandate that Iowa builders follow these codes. This project has attempted to answer questions of how much energy savings can be achieved by implementing energy savings steps described in 2000 IECC. A total of 30 homes were selected for this study with 10 homes located in each of the three weather regions of Iowa (i.e., northern, central and southern regions). The study restricted the energy used by each home to natural gas for heating and electricity for cooling. The three basic home styles included in the study were ranch-style, 2-story and split-level/1-1/2 story homes. Raw data was collected for each home through an in-home energy audit and utility data for natural gas and electricity for a two-year period. The raw data was normalized by using the heating degree day data for each weather region. The additional cost of building homes to 2000 IECC standards compared to more conventional building practices (i.e., either current practices or low efficiency practices) was determined for a range of floor areas and for the three main home styles, namely, ranch, 2-story and split-level. The additional costs were for materials, labor and equipment to install extra insulation in walls, ceilings and ducting. Costs were also considered for sealing ducts by using tape and for installing windows with higher U-values as specified in 2000 IECC. The reduced energy consumption for heating and cooling for 2000 IECC homes compared to homes built to lesser standards was determined for a range of home styles and sizes. The annual energy consumption along with annual heating and cooling loads were determined by using Energy 10. The models of the 2000 IECC, current practice and low efficiency homes were distinguished in each Energy 10 analysis by using different wall R-values, ceiling R-values and window U-values. The cost savings of operating 2000 IECC homes was found by taking the various differences in annual operating costs. A simple payback period analysis was performed by dividing the additional material costs to build homes to 2000 IECC standards by the operating cost savings. These payback periods varied from a low of 4.1 years to a high of 6.4 years.