So far only two states - Maryland and Vermont - have adopted the 2015 International Energy Conservation Code (IECC). But that doesn't mean a lot more might adopt it, or important provisions from it, very soon.
In particular, there are two provisions that stand out. One is a clear reference to a blower door standard. This sounds simple enough; nothing ground breaking here. Only, the previous version of the 2012 energy code radically upped the ante for air sealing - going from 7 ACH50 to 3 in climate zone 3 through 8 - without specifying how that requirement should be verified. The 2015 revision provides an important reference to the allowable ASTM standard blower door tests ... ones that are rigorous enough, it should be noted, that many builders are unlikely to subsume them into their building process without assistance from home-performance pros.
The other big update that may speed adoption of the 2015 energy code is the ERI - or Energy Rating Index. An ERI provides a simple way for homebuyers to compare the energy efficiency of one house to another. The lower the number, the more energy efficient the home, with zero being a net-zero home. Builders will benefit from this because they now have three compliance paths to choose from: the ERI compliance path, the prescriptive path, and the performance path.
The surprising part - which might be viewed as good or bad, depending on your stance on government-mandated home energy performance - is that meeting the basic requirements of the ERI path yields a home that more closely matches a home built to the 2009 IECC than the more energy-efficient home built to comply with the prescriptive or performance paths of the 2015 IECC. Read more.