Why the "Same" Home Can Have Different Scores

An E-Star Energy Rating a home receives as a result of a From-Plans can vary from the same home’s Final rating. Further, many builders notice that two homes of the same model will sometimes have varying Final ratings. These differences are due to modeling factors in From-Plans ratings and actual construction conditions in homes once they are built and not any random error or glitch in the E-Star rating system.

The scoring difference between a From-Plans and Final rating can be due to the method of calculation for the From-Plans rating and differences in the physical properties of the actual homes once they are constructed. For instance, From-Plans ratings are calculated based on a worst-case scenario in regards to home orientation. The greatest area of window exposure is oriented to the north or west for calculation purposes in the From-Plans rating. However, the actual home may have windows facing almost entirely to the south or east; therefore, the Final rating will have a much higher score than that of the From-Plans rating.

In the case of two homes built from a single set of plans, one home’s orientation may be more advantageous, or enjoy shading from neighboring buildings or trees, thereby scoring higher than a neighboring unit. Homes built from the same plans may also have different ratings due to variations in construction, such as tightness of the building envelope, the quality of materials used, and how contractors install those materials.