The IECC 2018 states that the residential provisions apply to "Residential Buildings", which are defined as "detached one- and two-family dwellings and multiple single family dwellings (townhouses) as well as Group R-2, R-3 and R-4 buildings three stories or less in height above grade plane". This definition excludes buildings with transient occupants, such as hotels and boarding houses, but it includes most other low-rise housing.
NJ DCA Bulletin 19-2 clarifies that "Low-rise residential buildings are defined as one- and two-family dwellings or multiple family buildings three stories or less in height."
Like the 2015 IECC, the 2018 IECC includes a section (Chapter 5, Existing Buildings) clarifying that it is intended to apply to additions and major renovations in addition to newly constructed dwellings.
The NJ DCA Bulletin 19-2 states that builders must "show compliance with the Energy Subcode as part of the permit application process for a newly-constructed building or an addition."
However, "Buildings undergoing a repair, renovation, alteration, reconstruction or change of use must only meet the requirements provided for at N.J.A.C. 5:23-6, the Rehabilitation Subcode." In general, this subcode requires insulation levels matching the IECC 2018 when cavities are opened, but it does include specific requirements for air sealing, duct sealing, or mechanical ventilation.
Editorial Comment:
The 2015 & 2018 IECC require testing to verify that whole envelope air leakage and duct leakage rates fall below specified thresholds. This testing will is chllenging to complete accurately when testing additions, where the leakage of the existing structure can affect the test results of the new components. Successful implementation of the new existing building requirements requires a degree of cooperation and improvisation by builders, testing contractors, and code officials.
