Significant changes to the 2018 International Residential Code

The 2018 Significant Changes guides are available for the International Building, Residential, Fire, Plumbing, Mechanical and Fuel Gas Codes. This valuable series can help any code user save time by zeroing in on the most critical changes in the 2018 International Codes (I-Codes). The Code Council’s technical experts provide summaries, analysis and graphics for these changes making them clear and easy to understand.

2018 International Residential Code

A modification to Section N1102.2.2 (Reduction of Ceiling Insulation) states that when applying the exception for insulation in ceilings without attics, the insulation must extend to the outside of the top plate.

The International Residential Code (IRC) offers two exceptions to the prescriptive ceiling insulation requirements. The first, in Section N1102.2.1, Ceilings with Attic Spaces, recognizes the effectiveness of energy (raised heel) trusses. The increased height at the exterior wall plate allows for the full thickness of ceiling insulation throughout and the code accordingly allows a reduction in the required R-value. The second exception, in Section N1102.2.2, Ceilings without Attic Spaces, recognizes the difficulty of achieving the full required thickness of insulation in vaulted or cathedral ceilings framed with solid-sawn dimension lumber rather than trusses. In this case, the code allows a reduction in R-value to R-30 for a maximum area of 500 square feet. Depending on the Climate Zone, this is a reduction from R-38 (Zones 2 and 3) or R-49 (Zones 4 through 8).

The changes to this section for the 2018 IRC are primarily editorial. For clarification, “greater than” replaces “above” in reference to the R-30 baseline value. The concern was that the phrase “above R-30” could be read as physically above (higher) or providing a higher level of insulation. The term “greater than R-30” reflects the intent and is consistent with other provisions in the IRC. A new sentence emphasizes that in order to take advantage of this exception, the insulation needs to maintain that minimum R-value of R-30 over the entire area of the ceiling, including extending to the outer edge of the top plate at the exterior wall. Compression of the insulation at any point reduces the R-value and is less effective at conserving energy. While many code users have inferred that the intent was to maintain the R-value to the outside of the exterior wall, the code previously did not explicitly require it.

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