Air leakage causes significant energy losses in buildings and depends on local pressure gradients caused by temperature differences and wind. Airtightness requirements of the 2012 International Energy Conservation Code change by location. However, airtightness codes do not consider resistance caused by air leakage from wind-driven pressure gradients, only temperature-difference-driven pressure gradients. Codes for thermal resistance also don’t reflect reductions in thermal performance caused by air leakage, excluding air leakage completely in thermal resistance calculations. Air leakage needs to be included in thermal resistance codes and wind factors need to be included in airtightness standards to better understand how air leakage affects overall thermal performance.We simulated a 40 × 25 ft (12 × 7.6 m), two-story home with three different levels of airtightness to study effective thermal resistance. We also modeled the home with codecompliant airtightness to study energy loss through the building envelope as a function of localized weather. With the results, we generated contour maps to visualize trends of increased energy loss and decreased thermal resistance of code-insulated homes across the United States. These results indicate that present code requirements do not effectively account for the impact of air leakage on thermal performance or reveal where in the United States airtightness of buildings most affects energy performance.