NORTHVILLE, MI (February 23, 2021) – Newly adopted residential building codes set by the International Energy Conservation Code (IECC) are about to become the standard for homes built in the Tennessee counties of Davidson, Williamson, Maury, Rutherford, and Sumner. Starting March 1, 2021, these counties will move from the IECC’s 2012 standards to the code’s 2018 benchmarks, which means all residential construction must meet a minimum insulation value of R-20.