Kentucky REScheck Requirements (2026)

Key facts:

• 2009 IECC with KY Amendments — Current

• Statewide Zone 4A

• Mini-Maxi Code — Uniform Statewide

• Blower Door: 7 ACH50 or Visual Inspection

 

Kentucky commonly requires REScheck for: new residential construction, residential additions and alterations, conditioned detached structures, barndominiums and ADUs. REScheck is explicitly recognized as approved compliance software. The code is uniform statewide — no local jurisdiction may weaken it. Kentucky's energy code is among the least restrictive in the nation: lenient insulation values, a 7 ACH50 blower door threshold (or visual inspection), and no SHGC requirement statewide.

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Kentucky jurisdictions require REScheck and energy compliance documentation under the Kentucky Residential Code (815 KAR 7:125), administered by the Kentucky Department of Housing, Buildings and Construction (DHBC). The current residential energy code is the 2009 International Energy Conservation Code with Kentucky amendments — effective September 1, 2019, and still the enforced standard in 2026.

 

⚠ Kentucky's Residential Energy Code Is the 2009 IECC — Still in Effect in 2026: Despite adopting the 2018 Kentucky Residential Code (based on the 2015 IRC, most recently updated to the 3rd Edition effective August 1, 2024) for structural provisions, the energy chapter still explicitly references Table 402.1.1/402.1.3 of the 2009 IECC for all thermal envelope requirements. As of 2026, Kentucky's residential energy code is more than 15 years old. The Midwest Energy Efficiency Alliance urged DHBC in January 2025 to adopt the 2021 or 2024 IECC, but no update has been enacted.

 

Statewide Code Structure

Kentucky's residential energy code is embedded in Chapter 11 of the Kentucky Residential Code (815 KAR 7:125). The KRC is a “mini-maxi” code — mandatory, uniform, and statewide for all one- and two-family dwellings and townhouses. No local government may adopt or enforce a conflicting building code.

• 2009 IECC with Kentucky amendments — effective September 1, 2019

• Applies statewide to all one- and two-family dwellings and townhouses

• No local jurisdiction may adopt a weaker energy code — mini-maxi code structure

• Update to 2021 or 2024 IECC recommended but not yet enacted as of 2026

• Commercial buildings: 2012 IECC with amendments (effective September 1, 2019)

 

Common Permit Requirements

• Energy compliance documentation — prescriptive checklist, REScheck (UA trade-off), or performance simulation

• Window and door schedule (U-factor and SHGC per NFRC)

• Insulation R-value specifications and installer certification

• Air leakage compliance — blower door test (7 ACH50 max) OR visual inspection per Table 402.4.2

• Duct leakage test results — required for all systems in unconditioned spaces (effective July 1, 2015)

• HVAC equipment sized per ACCA Manual J (Section 403)

• High-efficacy lighting — min. 50% of permanently installed lamps

• Energy certificate posted at electrical panel at completion

 

Kentucky's Three Compliance Pathways

Pathway  ·  How It Works

• Prescriptive (§402.1.1):  Ceiling R-38, walls R-13+5ci or R-20, floor R-13, basement R-10/13, window U-0.35, SHGC 0.40. No REScheck needed — checklist submitted with permit.

• UA Trade-Off — REScheck:  Total UA ≤ reference design UA (§402.1.4). REScheck explicitly recognized. SHGC still must be met, can't be traded off.

• Simulated Performance / ERI:  Whole-building simulation (§405); proposed annual energy cost ≤ standard reference design. ERI path available under Ch. 11 of 2018 KRC.

 

Kentucky Climate Zone

Kentucky is entirely in IECC Climate Zone 4A (Mixed-Humid) — no Zone 5 counties. The entire state, from Paducah to Pikeville and Covington to Middlesboro, is Zone 4A. The same insulation values apply statewide.

Zone  ·  Coverage  ·  Classification  ·  Key Requirements

• 4A:  Entire state — Louisville, Lexington, Bowling Green, Owensboro, Paducah, Covington, Frankfort, Florence, Elizabethtown, Ashland, Pikeville, Hazard, Somerset, Richmond, Hopkinsville   —   Mixed-Humid   —   Ceiling R-38, walls R-13+5ci or R-20, floor R-13, basement R-10/13, window U-0.35, SHGC 0.40, blower door 7 ACH50

 

Zone 4A Prescriptive Requirements (2009 IECC Table 402.1.1)

• Ceilings: R-38 min (R-30 satisfies at eave condition)

• Wood Frame Walls: R-13+5ci OR R-20 cavity-only

• Floor: R-13 min

• Basement Walls: R-10/13 — Kentucky amended to require only top-of-wall-to-frost-depth (24–33 in.), not full wall height

• Crawlspace Walls: R-10/13

• Slab Edge: R-10 at 2 ft depth

• Window U-factor: max 0.35 (NFRC-labeled)

• SHGC: max 0.40

• Skylight U-factor: max 0.60

• Opaque Door U-factor: max 0.35 (one side-hinged door up to 24 sq ft exempt)

• 15 sq ft glazing exemption from U-factor/SHGC on the prescriptive path

 

Kentucky Basement Amendment: insulation is only required from the top of the basement wall to the design frost depth (24–33 inches) — not the full wall height. This is a Kentucky-specific reduction from the base 2009 IECC.

Kentucky's requirements are among the least demanding in the country for a Zone 4A state. Neighboring states are stricter: Indiana (2018 IRC, R-49 ceiling in Zone 5A), Illinois (2024 IECC, 3 ACH50 mandatory), Tennessee (2018 IECC with amendments). Builders crossing state lines need to significantly upgrade specs.

 

Air Leakage and Duct Requirements

Air Leakage Compliance (§402.4)

• Option A — Blower Door Test: less than 7 ACH50 at 50 pascals, tested after rough-in with envelope penetrations installed

• Option B — Visual Inspection: envelope tightness accepted per Table 402.4.2 field verification

• 7 ACH50 matches South Carolina and Wisconsin as the most lenient threshold among states that permit testing

• Both paths fully valid; no preference stated in the code

 

Duct Leakage Requirements (§403.2.2)

• Effective July 1, 2015: all residential duct systems in unconditioned spaces must be pressure tested

• Post-construction: max 8 CFM25 per 100 sq ft

• Rough-in (with air handler): max 6 CFM25/100 sq ft; (without): max 4 CFM25/100 sq ft

• Testing required only when ducts are outside the thermal envelope — conditioned-space ducts exempt

• Duct insulation: R-8 supply ducts in attics; R-6 all other ducts outside thermal envelope

 

Is REScheck Required in Kentucky?

• New single-family homes

• Duplexes and townhomes

• Conditioned residential additions and alterations

• Finished basement conversions

• Garage conversions to conditioned space

• Conditioned sunrooms and bonus rooms

• Conditioned barndominiums

• Accessory dwelling units (ADUs)

 

Mini-maxi code: the KRC is both a minimum AND maximum standard — no local jurisdiction can require stricter or weaker provisions. Louisville, Lexington, and all 120 counties enforce identical requirements.

 

Common REScheck Failure Reasons in Kentucky

Most Common Errors

• Using newer IECC values — builders familiar with Indiana or Illinois sometimes apply those states' higher values, which aren't the enforceable Kentucky standard

• Basement wall insulation depth error — Kentucky only requires insulation to design frost depth (24–33 in.), not full height; using full-height R-10/13 adds unnecessary cost

• Missing or exceeded SHGC 0.40 — large window packages on south/west walls frequently propose higher values

• Window U-factor above 0.35 maximum

• R-13+5ci wall assembly incorrectly entered — if structural sheathing covers more than 25% of exterior, supplemental insulated sheathing of at least R-2 is required

 

Mechanical & Field Issues

• Missing duct leakage documentation — required since July 1, 2015 for unconditioned-space duct systems

• Duct leakage failures — unsealed boots, improper mastic, deteriorated duct tape in hot humid summers

• Missing insulation installer certification for blown/sprayed insulation

• HVAC not sized per Manual J (§403) — oversized equipment common without documentation

• Framing cavity used as duct — prohibited under §403.2.3

• Missing energy certificate at final inspection

 

Major Cities and Jurisdictions

Louisville (Jefferson County) — Zone 4A

Kentucky's largest city and most active market. Louisville Metro Building Inspections enforces the KRC including 2009 IECC provisions. Ohio River location and urban heat island make SHGC control particularly important.

 

Lexington (Fayette County) — Zone 4A

Second-largest city, home to the University of Kentucky. Same 2009 IECC requirements as everywhere else in the state.

 

Bowling Green & Warren County — Zone 4A

One of Kentucky's fastest-growing markets, driven by the Corvette plant, WKU, and migration from Tennessee. Kentucky's code is more lenient than Tennessee's 2018 IECC.

 

Owensboro (Daviess County) — Zone 4A

Western Kentucky, Ohio River corridor. Builders crossing into Indiana (Evansville) should note Indiana's stricter 5 ACH50 requirement vs. Kentucky's 7 ACH50.

 

Covington & Northern Kentucky (Boone, Kenton, Campbell) — Zone 4A

Cincinnati-adjacent counties. Ohio's residential code (2021 IECC, mandatory 3 ACH50) is far stricter than Kentucky's 7 ACH50 or visual inspection.

 

Eastern Kentucky (Pikeville, Hazard, London) — Zone 4A

Appalachian counties, still Zone 4A despite higher elevation. Enforcement capacity varies; visual inspection commonly used.

 

Frequently Asked Questions

What energy code does Kentucky currently use?

The 2009 IECC with Kentucky amendments, effective statewide September 1, 2019, incorporated into Chapter 11 of the Kentucky Residential Code (815 KAR 7:125). As of 2026, this code is more than 15 years old; no update to the 2021 or 2024 IECC has been enacted.

 

Is blower door testing required in Kentucky?

No, not mandatory. §402.4.2 offers two equally valid paths: a blower door test under 7 ACH50, or visual inspection per Table 402.4.2. The 7 ACH50 threshold is among the most lenient of any state permitting testing.

 

What climate zone is Kentucky in?

Entirely IECC Zone 4A (Mixed-Humid) — the whole state uses the same insulation values. Prescriptive requirements: ceiling R-38, walls R-13+5ci or R-20, floor R-13, window U-0.35, SHGC 0.40.

 

Is duct leakage testing required in Kentucky?

Yes, but only when ducts are in unconditioned spaces (DHBC notification effective July 1, 2015). Post-construction max is 8 CFM25/100 sq ft. Ducts entirely within conditioned space don't require testing.

 

What is the Kentucky basement wall insulation requirement?

Insulation is required only from the top of the basement wall to the design frost depth (typically 24–33 inches below grade), not full wall height, at R-10/13 — a Kentucky-specific reduction from the base 2009 IECC.

 

Can local jurisdictions in Kentucky adopt stricter energy codes?

No — the KRC is a mini-maxi code, both minimum and maximum. Louisville, Lexington, and all 120 counties enforce exactly the same requirements, unlike states such as Maryland or New Jersey where locals can go stricter.