2021 I-Codes Adoption Kit

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Contact: Craig Drumheller
cdrumheller@nahb.org
(202) 266-8565

Jurisdictions at the state or local level periodically update the building code requirements. During the code adoption process, there are typically questions related to the new changes and cost impacts of the code edition being considered for adoption.. This kit addresses these concerns for adoption of the 2021 I-Codes and provides NAHB-suggested amendments that take into account concerns from builders, including cost-effectiveness and payback for home buyers

The 2021 I-Codes Adoption Kit consists of three parts:

  • Significant changes that were made in the 2021 I-Codes from the 2018 editions: One section for single-family construction and another for multifamily.
  • Cost impact of adopting the 2021 IRC relative to the 2018 edition.
  • NAHB-suggested amendments to improve the codes’ practicality and cost effectiveness.

Note: For Chapter 11 - Energy Efficiency of the IRC, see the code adoption information on the 2021 International Energy Conservation Code page.

Significant Changes to the 2021 IRC

This summary includes changes to the International Residential Code (IRC). This is not all of the changes that were approved. Download the 2021 Significant Code Changes for the IRC for a list of the significant changes, which are also provided here:

  • IRC Section R301.2.1.2 Protection of openings: Wind-borne debris protection in hurricane-prone regions is now required for any site within one mile of the mean high- water line of an Exposure D condition instead of just one mile from a coastal mean high- water line. This will include buildings adjacent to wide rivers or large inland lakes but not directly fronting on the Atlantic Ocean or Gulf of Mexico.
  • IRC Section 301.2.2.6 Cripple Wall Clear Height: Hillside light-frame construction is added as an irregular building type to be addressed by an engineered design for the transfer of lateral forces from the house to the foundation. The irregularity applies where the slope exceeds 1-unit vertical in 5-units horizontal, the tallest cripple wall clear height exceeds 7-feet and the area under the lowest floor is less than 50% finished space.
  • IRC Section 301.3 Story Height: The ability is restored to construct a story of a dwelling using 12-foot high bearing walls if the wall studs are engineered for gravity loads, wall bracing amounts are increased, and a roof or celling diaphragm provides support to the studs.
  • IRC Section Table 301.5 Minimum Uniformly Distributed Live Loads: The live load requirement for guards and handrails are separated, and guards are only required to resist a 200-pound load in the outward and downward directions. The change would reduce the amount of connection hardware needed to construct a guard along a deck or other elevated walking surface.
  • IRC Section 326 Habitable Attics: Habitable attics are required to be considered a story above grade plane unless it meets the same restrictions as mezzanines. A dwelling may need to be sprinklered in order to permit a habitable attic to be constructed.
  • IRC Tables 403.1(1), 403.1(2), 403.1(3) Minimum Thickness for Concrete Footings for Light-Frame Construction: The minimum footing width tables are revised to remove overly conservative assumptions or correct underlying calculations to match common engineering practice for light-frame construction. In most cases footing sizes will be modestly reduced from the 2015 and 2018 IRC requirements.
  • IRC Sections 403.1.6 Foundation Anchorage: Requirements are added for wet-setting of anchor bolts in foundations, including the need for proper consolidation of concrete around wet-set bolts.
  • IRC Section 703.4 Flashing at Window and Door Openings: An insulation stop is required be installed around window and door openings to allow for drainage of water to the surface of the exterior wall finish. The insulation stop is to be located 1 to 2 inches from the face of exterior sheathing.
  • IRC Sections 703.7 Lath and Furring: The lath and attachment requirements for exterior lath and plaster (stucco) are revised to correlate with ASTM C926 and C1063 and attachment and placement requirements for furring. Fasteners for lath are required to be spaced 7 inches vertically along studs or furring and horizontally at the spacing of the studs or furring.
  • IRC Sections 703.7.3 Water Resistive Barriers: The water-resistive barrier requirements behind stucco where applied to wood-based sheathing are divided into separate sections for dry and moist climate zones. A 3/16-inch air space or material with high drainage efficiency is required in moist climate zones.
  • IRC Tables N1102.1.2 and N1102.1.4 Insulation and Fenestration Requirements: Prescriptive wall, ceiling and slab edge insulation levels are increased as follows:
    • Wall insulation in Climate Zones 4 and 5 increased from R-20 in the cavity to R- 20 in the cavity +R-5 continuous.
    • Slab edges in Climate Zone 3 are required to be insulated with a minimum R-10 at 2-foot depth.
    • The depth of the required R-10 slab edge insulation for Climate Zone 4 and 5 is increased from 2 feet to 4 feet minimum.
    • Attic insulation levels are increased in Climate Zones 2 and 3 from R-38 to R-49, and in Climate Zones 4-8 from R-49 to R-60.
  • IRC Sections N1104.1-N1104.2 Lighting Controls: 100% of permanently installed lighting fixtures must have high efficacy lamps with efficiency of as 70 lumens per watt. All permanently installed lighting fixtures must have dimmers or occupant sensor controls.
  • IRC Section N1105.2 Performance-Based Compliance: A backstop is added in the performance path requiring the building thermal envelope to achieve equal or greater levels of energy efficiency to the 2009 IECC.
  • IRC Tables N1105.4.2(1) and N1103.6.2 Mechanical Ventilation Reference Design: The mechanical ventilation system used in the standard reference design used in a performance path analysis is required to be the same system used in the proposed design. The table of whole house mechanical ventilation fan efficacy is modified to specify fan efficacy by system type rather than fan location.
  • IRC Section N1106.3 Energy Rating Index: The maximum Energy Rating Index (ERI) thresholds are lowered by 5-8 points (9-13% increase in stringency) depending on the climate zone. In addition, the amount of total energy use reduction from on-site renewable is limited to 5%.
  • IRC Section 1101.6 and 1106.6 Renewable Energy Certificate and Verification: A renewable energy certification is required to be given to the code official when on-site renewables are used in the ERI path. The certificate must demonstrate the homeowner owns the solar energy system or that a certain quantity of the energy generated belongs to the homeowner.
  • IRC Section N1101.13.5 Additional Efficiency Package Options: An additional efficiency package is required beyond base requirements. It is intended to increase stringency by about 5% of building energy use. For prescriptive or performance path, five individual packaged options are added: (1) insulation and glazing, (2) HVAC, (3) water heating, (4) ducts entirely within conditioned space, and (5) air sealing and ventilation. Performance path may choose a 5% modeled improvement in lieu the package requirement. ERI requires a 5% improvement over its baseline.
  • IRC Section P2905.3 Hot Water Supply to Fixtures: A new section is added limiting the maximum length of hot water piping to 100-feet.
Significant Changes to the 2021 IBC and Related Codes for Multifamily

This summary includes changes to the International Building Code (IBC), International Energy Conservation Code (IECC), International Fire Code (IFC), and International Mechanical Code (IMC). No significant changes were identified for the International Existing Building Code (IEBC) or International Plumbing Code (IPC). This is not all of the changes that were approved. Download the 2021 Significant Changes for Multifamily, for a list of the significant changes, which are also provided here:

2021 IBC

  • Section 504.3 Height in Feet. Table 504.3 is revised to add allowable heights for three new types of mass timber construction: Type IV-A, IV-B and IV-C. Group R sprinklered buildings can be 270, 180 or 85 feet in height for the three new types, respectively.
  • Section 504.4 Number of Stories. Table 504.4 is revised to add allowable stories for three new types of mass timber construction: Type IV-A, IV-B and IV-C. Group R sprinklered buildings can be 18, 12 or 8 stories for the three new types, respectively.
  • Section 506.2 Allowable Area Determination. Table 506.2 is revised to add allowable area factors for three new types of mass timber construction: Type IV-A, IV-B and IV-C. For Group R sprinklered buildings the factor is up to 246,000 square feet for the first floor and 184,500 square feet for upper floors.
  • Section 1206 Sound Transmission. The requirements for protecting against airborne or structure-borne sound transmission are expanded to apply to separations between dwelling or sleeping units and all public spaces, not just corridors and stairs.
  • Section 1604.5 Risk Category. The list of buildings assigned to Risk Category III is revised to include buildings with one or more public assembly spaces with an occupant load exceeding 300 people and a cumulative public assembly occupant load of more than 2,500 people. The change allows more flexibility in what tenants could occupy commercial spaces in a mixed-use residential building.
  • Section 1609.2 Protection of Openings. Wind-borne debris protection is now required for any site within one mile of the mean high-water line of an Exposure D condition instead of just one mile from a coastal mean high-water line. This will include buildings adjacent to wide rivers or large inland lakes but not directly fronting on the Atlantic Ocean or Gulf of Mexico.

2021 IECC

  • Table R402.1.2 Maximum Assembly U-Factors and Fenestration Requirements. Prescriptive wall, ceiling and slab edge insulation levels are increased as follows:
    • Wall insulation in Climate Zones 4 and 5 increased from R-20 in the cavity to R-20 in the cavity +R-5 continuous.
    • Slab edges in Climate Zone 3 are required to be insulated with a minimum R-10 at 2-foot depth.
    • The depth of the required R-10 slab edge insulation for Climate Zone 4 and 5 is increased from 2 feet to 4 feet minimum.
    • Attic insulation levels are increased in Climate Zones 2 and 3 from R-38 to R-49, and in Climate Zones 4-8 from R-49 to R-60.
  • R403.3.5 Duct Testing. Ducts located inside conditioned space are now required to be tested for air leakage. The maximum leakage threshold is set at 8.0 cfm per 100 square feet of conditioned floor area.
  • R404.1 Lighting Equipment. 100% of permanent lighting fixtures must have high efficacy lamps with efficiency of 70 lumens per watt (most LED, some CFL, most florescent tubes will comply).
  • R404.2 Interior Lighting Controls. With some exceptions such as in bathrooms and hallways, all permanent lighting fixtures must include dimmers or occupant sensor controls.
  • R405.2 Performance-Based Compliance. A backstop is added in the performance path requiring the building thermal envelope to achieve equal or greater levels of energy efficiency to the 2009 IECC.
  • Table R406.5 Maximum Energy Rating Index. The maximum Energy Rating Index (ERI) thresholds are lowered by 5-8 points (9-13% increase in stringency) depending on the climate zone. In addition, the amount of credits available for onsite renewable energy is limited.
  • R406.7.3 Renewable Energy Certificate (REC) Documentation. A renewable energy certification must be given to the code official when on-site renewables are used in the ERI path. The certificate must demonstrate the homeowner owns the solar or that a certain quantity belongs to the home owner.
  • R408.2 Additional Efficiency Package Options. An additional efficiency package is required beyond base requirements. It is intended to increase stringency by about 5% of building energy use. For prescriptive or performance path, five individual packaged options are added: (1) insulation and glazing, (2) HVAC, (3) water heating, (4) ducts entirely within conditioned space, and (5) air sealing and ventilation. Performance path may choose a 5% modeled improvement in lieu the package requirement. ERI requires a 5% improvement over its baseline.
  • C402.5.1.2 Air Barrier Compliance. Air-barrier testing for Group R and I occupancies are separated from the testing requirements for all other occupancies. New requirements are added for testing of non-residential buildings.
  • C402.5.2 Dwelling and Sleeping Unit Enclosure Testing. Air-barrier testing of dwelling units and sleeping units in all buildings 4 or more stories in height is now required.
  • C403.7.4 Energy Recovery Systems. Non-transient dwelling units are required to have outdoor energy recovery ventilation based on an enthalpy recovery ratio of not less than 50%.

2021 IFC

  • Section 903.3.1.2 [IBC [F] 903.3.1.2.3] NFPA 13R sprinkler systems. The maximum floor level of the highest story where NFPA 13R systems in Group R occupancies can be used is reduced from 60 feet above grade to 30 feet above the lowest level of fire department access.

2021 IMC

  • Section 401.2 Ventilation Required. Mechanical ventilation is now required for all multi-family dwelling units.
Cost Impact for Adoption of the 2021 I-Codes

A report on the Estimated Costs of the 2021 IRC Code Changes by Home Innovation Research Labs is in progress and will describe the cost impact for typical homes in terms of both increases and savings over the 2018 International Residential Code. These typical values will vary based on the climate zone and house configuration.

Suggested Amendments

NAHB has prepared recommendations for amending the 2021 International Residential Code, and other 2021 ICC model codes. Each recommended amendment is provided in a draft form that includes the code section and text to be amended in legislative format (underline), a reason statement, and an NAHB staff contact.

Each suggested amendment should be considered individually to ensure that it is an improvement for the jurisdiction. Priorities can differ from region to region, and HBAs should not hesitate to consider alternative code text that may be more appropriate. If there are any questions on the change or an HBA is looking for assistance on modifying the amendment, please contact NAHB staff for assistance.

Suggested Amendments to the 2021 I-Codes

Related Resources

Fire sprinkler requirements for one- and two-family homes continue to be part of the International Residential Code, despite significant consumer resistance and debunked claims to their necessity. NAHB’s Fire Sprinkler resource page remains an excellent resource for removing these requirements.

In addition, resources on energy and arc fault interrupters can be found on the Energy Codes page and the Arc-Fault Circuit Interrupters information page.

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