NC Building Code Insulation Requirements

On January 1, 2019, the 2018 North Carolina Building Code (based on the 2015 IECC with amendments) went into effect. This new code should stay for at least 3 years, since NC typically runs a 3-year code cycle, and the 2012 NC building code was in effect for 6 years.

Insulation Requirements for NC Building Code

The building code requires structures to have certain R-values* for the state based on different locations and climates. Wake County is a 4A zone, so walls, floors, ceilings, and slab insulation values are unchanged from the 2012 code.

Insulation R-Values for NC Building Code

  • R-19 on floor system/garage ceiling
  • R-15 on exterior walls
  • R-38 for the ceiling/attic

So what does this mean for MPI Foam?

We run a performance calculation of the insulation envelope for our inspectors during the insulation inspection, since the spray foam that is installed typically doesn’t meet the prescriptive R-values in the walls and roof decks.

However, spray foam insulation normally performs much better than its prescriptive R-value because of the air sealing properties, as well as its ability to create a complete fill on the walls and in roof cavities. 

To prove our spray foam insulation distributed within walls, floors, and roofs exceeds the current 2018 NC Building Code R-values, we have a third party energy rater run a performance or energy calculation. 


*R-Value: The capacity of an insulating material to resist heat flow. The higher the R-value, the greater the insulating power.


This article was updated in December 2021.

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