Accurate Review


2018 Residential Code

An Accurate Review White Paper, Summer 2017


By:  Don Olivieri, Architect



Significant Changes to the 2018 International Residential Code



This white paper is prepared to aid our Residential Building Clients and Governmental Code Enforcement friends and clients in understanding the changes that will be in the new addition of the IRC (International Residential Code). We also hope it prepares the architects and contractors become more familiar with the changes.  We want to help give insight to Governmental Code Enforcement Officials into what is coming and enable them to make an informed decision on its adoption.


Every three years, the International Code Council updates the family of Codes which include the International Residential Code (IRC). The IRC is the widely adopted throughout the country in whole or with various amendments. Many of the revisions are housekeeping in nature to clarify or move wording to make the code easier to use. However, there are always several significant changes to the code. With this paper we will give you a brief overview of the major revisions to the code.




There are now 5 options to conform to the High Wind requirements of R301.2.1.1. for our clients in these areas. The ASCE7-16 has been updated to increase roof components and cladding loads.




These changes are based on new United States Geological Survey (USGS) Seismic Design Categories which changed but only in southeastern New Hampshire, eastern Tennessee and Charleston South Carolina, the rest of the country map remains the same. Also a new map can be used when the owner obtains a Soils Report acceptable to the building official.




Section 302 brings back the option of using two separate 1 hour fire resistant rated walls assemblies to separate individual townhomes. Going this route also allows the building to utilize the cavity in each wall for plumbing and or mechanical systems.




The main change in Flood Resistance construction occurs in respect to exterior slabs adjacent to Zone V, and in respect to if the slab could be washed away. In this case the slab is allowed to be reinforced if designed per ASCE 24 and resistant to erosion and scour, or can be “frangible” 4 inch unreinforced with thickened edges (and providing joints at a maximum of 48” on center each direction).


Additionally Stairs and ramps (Zone V) must have “break-away” enclosures under stairs or no enclosure at all. Also stairs and or ramps cannot be “Break away” if they are a means of egress. Stairway or ramps that can be raised are the other method of complying with this section.




They’ve added to the table single ply beams, but very limited use is allowed. They also added 8 x 8 posts to allow higher decks. Also, there is a new table of minimum footing sizes and typical concrete pier and footing details.




For engineering based studs the table exception has been revised making it easier to enforce for 20 feet high studs. There are new sections on 11 and 12 foot high load bearing studs with 12 foot or 24 foot floor or roof framing.




The main changes concerns the minimum number of king studs provided and the separation of low-wind urban and suburban conditions from high-wind and open exposures. The king stud provision in low-wind, urban or suburban areas is the one area that the code is less demanding, but more defined.




In low wind area nothing changes except the requirement that manufacturer soffits need to be attached according to the manufacturer’s instructions, and all wood soffits must have the same thickness of the siding (minimum). The main changes were intended to address the soffit failures in high wind areas.




The 2018 IRC now has new provisions for brick tie attachments over foam that is over 2” thick and it also requires minimum 7/16” plywood or OSB sheathing behind the foam sheathing. We, however, recommend this section be upgraded to require ½” sheathing. Additionally they have finally addressed the tie attachment; over the years we have seen many issues due to poor attachment and have often recommended an additional attachment requirement. The IRC will now have a ring shank nails or screw requirement. And finally the spacing of this attachment has been reduced to 12” both vertically and horizontally.




The changes here occurred mainly for our friends in climates zones 1, 2 and 3.  No changes for those of us in climate zones 4 and 5.




The 2018 IRC will now allow log homes that can meet the thermal envelope requirements of the ICC 400 Standard. This is in conflict with the State of Illinois Energy Code, therefore an AHJ adopting this will need an amendment for this section to match State Law.




The code continues to lower U-Values on windows which correspond to lower heat loss and better energy efficiency. This time U-factors will reduced from 0.35 to 0.32 for Climate Zones 3 and 4 and from 0.32 to 0.30 from climate zones 5 thru 8.




Ductwork is now allowed to be incorporated within the attic insulation, however the building envelop insulation still has to be a minimum of R-19 either above, below or both above and below the ductwork. You cannot count any of the ductwork insulation in this R-value. New is all ducts must be inside a vapor retarder exterior jacket and have an R-value of 8 or better (R-13 or better for Climate Zones 1A, 2A, & 3A).


If you want your attic ductwork to be considered inside a conditioned space (N1103.3.7) all four of these requirements must be met. 1.) The duct is buried per section N1103.3.6 2.) The required attic insulation per the building envelope requirements must be above the duct. 3.) The air handing unit must be in a conditioned space and 4.) The maximum duct leakage is limited to 1.5 cubic feet per minute per 100 square feet of conditioned space; note there are neither adjustments for ceiling heights, vaulted nor cathedral ceilings.


Referring to section M1601.4.1 regarding duct sealing there is now an exception that allows transverse and longitudinal joints, seams, and connections not to be sealed when located within conditioned spaces.




The 2018 IRC now adds ANSI/RESNET/ICC 301 “Standard for Calculation and Labeling of the Energy Performance of Low-Rise Residential Buildings using and Energy Rating Index” as a new added Reference Standard. The actual ERI minimum rate number to be meet has actual been reduced making it easier to obtain the required number (or lower, because a lower ERI is better). However this Index is still more stringent than the Prescriptive path.


We hope this gives you and quick summary of the newest IRC which you may consider adopting in the near future.


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