The Alabama energy code is a state-amended version of the 2015 International Energy Conservation Code (IECC), and it sets minimum standards for insulation, windows, HVAC equipment, air sealing, and duct tightness on every new building and major renovation that requires a permit. Because Alabama’s amendments relax several national IECC values, you have to build to the state’s numbers, not the base code’s. Two performance tests, a blower door test and a duct leakage test, are mandatory before you can get a Certificate of Occupancy.
Which Code Edition Applies
For residential construction, Alabama enforces its amended 2015 IECC, effective October 1, 2016.1Building Energy Codes Program. Alabama Building Energy Codes Program The amendments matter. The unamended national code calls for R-38 ceiling and R-20 wall insulation in Climate Zone 3 and caps air leakage at 3 air changes per hour; Alabama’s version requires only R-30 ceilings, R-13 walls, and allows up to 5 ACH50. A builder who follows the wrong table over-insulates and overspends, or under-builds and fails inspection.
Commercial buildings comply with either the commercial portion of the 2015 IECC or ANSI/ASHRAE/IES Standard 90.1-2013, both effective January 1, 2016.2Cornell Law Institute. Alabama Admin Code Rule 305-2-4-.08 – Commercial Energy Code ASHRAE 90.1 excludes low-rise residential (single-family homes and multifamily buildings of three stories or fewer). You pick one standard and follow it in full.3U.S. Department of Energy – Building Energy Codes Program. Commercial and Residential Building Energy Codes
As of 2026, Alabama has not adopted any newer edition of either standard.1Building Energy Codes Program. Alabama Building Energy Codes Program
Climate Zones
Alabama splits into two IECC climate zones. Baldwin and Mobile counties, on the Gulf Coast, are Zone 2A. Every other county is Zone 3A. Your zone determines a few of the prescriptive values, especially for floors.
Prescriptive Minimums for Residential
Insulation R-Values
Under Alabama’s amended prescriptive tables, minimum R-values for residential work are:4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code
- Ceiling: R-30, both zones
- Wood-frame walls: R-13, both zones
- Floors: R-13 in Zone 2, R-19 in Zone 3
- Basement walls: not required in Zone 2; R-5 continuous or R-13 cavity in Zone 3, though this is waived in warm-humid locations, which covers most of the state
Window and Skylight Limits
Fenestration in both climate zones must meet:5Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-A – Residential Energy Code Tables
- Window U-factor: 0.35 maximum
- Solar heat gain coefficient (SHGC): 0.27 maximum
- Skylight U-factor: 0.55 maximum; skylights in Zones 1 through 3 may exceed the SHGC limit if they stay at or below 0.30
Every window sold in the U.S. carries a National Fenestration Rating Council label with the U-factor and SHGC printed on it, so verification at the product level is straightforward.
Projects That Must Comply
The energy code applies to all new residential and commercial construction requiring a building permit. It also covers additions that increase conditioned floor area and alterations that replace or modify the building envelope or mechanical systems.4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code When you replace windows, add insulation, or install new HVAC in a conditioned space, the new components must meet current code even if the rest of the building was built to an older standard.
A repair that restores materials or equipment to their original condition, such as replacing a broken pane with the same glass, does not trigger compliance. Swapping the entire window unit does, and the replacement has to meet the U-factor and SHGC limits.
Two categories fall outside the code. Buildings designated as historically significant by the local authority, listed on the National Register of Historic Places, or determined eligible for listing by the U.S. Secretary of the Interior are exempt. So are unconditioned structures with no heating or cooling systems.
Four Ways to Show Compliance on a Residential Project
Prescriptive Method
Follow the R-value, U-factor, and SHGC tables component by component. If every wall, ceiling, floor, and window meets or exceeds the values for your climate zone, you pass. No modeling, no trade-offs. Most production builders in Alabama use this path because it requires the least documentation.4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code
Trade-Off (UA Alternative) Method
Compensate for a weaker component by strengthening another. Want larger windows than the prescriptive U-factor allows? Offset the heat loss with higher ceiling insulation or a better wall assembly. The calculation compares the total heat transfer (the UA value) of your proposed building to a reference building that meets every prescriptive value. Equal or lower total UA passes.
Performance (Simulated) Method
A computer energy simulation models your proposed building’s annual energy use against a code-baseline building of the same size and shape. The proposed design must consume no more energy than the baseline. This path rewards design choices the tables can’t account for, like passive solar orientation, but it typically requires a professional energy modeler.
Energy Rating Index (ERI)
Alabama accepts compliance through an ERI score of 70 or lower.4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code The ERI scale runs from 100 (a 2006 IECC home) down to zero (net-zero energy), so 70 represents roughly a 30 percent improvement over a 2006-code home. A certified HERS rater performs a design-stage calculation plus on-site inspections and testing. Even under this path, the building still has to meet the mandatory air sealing and duct testing requirements and a minimum envelope standard equivalent to the 2009 IECC.
Commercial projects have parallel options under both the IECC commercial provisions and ASHRAE 90.1, including prescriptive, trade-off, and energy cost budget approaches.3U.S. Department of Energy – Building Energy Codes Program. Commercial and Residential Building Energy Codes
Mandatory Testing
Whichever compliance path you pick, two performance tests are required on residential projects. These aren’t optional; the building has to pass.
Blower Door Test
Every home is tested for air leakage with a blower door that depressurizes the building to 50 Pascals and measures how much outside air infiltrates. Alabama’s limit is 5 air changes per hour at 50 Pascals (5 ACH50) in both climate zones.4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code Fail, and the builder has to find and seal the gaps before retesting.
Duct Leakage Test
Ductwork is tested separately to confirm it isn’t losing conditioned air into attics or crawlspaces. Two thresholds apply:4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code
- Rough-in test: total duct leakage no more than 4 CFM per 100 square feet of conditioned floor area with the air handler installed, or 3 CFM per 100 square feet without.
- Post-construction test: total leakage to the outside no more than 4 CFM per 100 square feet of conditioned floor area.
On a 2,000-square-foot home, that’s 80 CFM at rough-in with the handler installed and 80 CFM to the outside after finish. Leaky ducts are where many projects fail their first test. The usual culprits are unsealed register boots and duct connections at the air handler.
Local Enforcement
Alabama writes the code, but county and municipal building departments handle permits and inspections.1Building Energy Codes Program. Alabama Building Energy Codes Program Enforcement varies. Urban jurisdictions with full-time code staff generally catch problems during plan review and scheduled inspections; some rural counties have minimal inspection capacity.
The typical sequence: the local building department reviews plans for energy code compliance before issuing a permit. During construction, inspectors verify insulation before drywall covers it and check HVAC and ductwork at mechanical rough-in. Blower door and duct leakage tests happen near the end. A Certificate of Occupancy is issued only after all required inspections and tests pass.4Alabama Administrative Code. Alabama Administrative Code Rule 305-2-4-.10 – Residential Energy Code
Without a Certificate of Occupancy, you can’t legally occupy the building, and lenders typically won’t close a mortgage on it. That’s the main enforcement lever in practice.
Section 45L Tax Credit for Builders
Builders of qualifying energy-efficient new homes in Alabama can claim a federal tax credit under Section 45L for homes acquired before July 1, 2026.6Department of Energy. Section 45L Tax Credits for DOE Efficient New Homes The credit was repealed for homes acquired after that date by the One Big Beautiful Bill Act, signed July 4, 2025.7Department of Energy. DOE Efficient New Homes Program
Credit amounts depend on certification level:
- $5,000 per home certified under the DOE Efficient New Homes program (formerly the DOE Zero Energy Ready Home program) when prevailing wage requirements are met, or $1,000 when they are not.
- $2,500 per home for ENERGY STAR-certified single-family, manufactured, or multifamily units, or $500 for ENERGY STAR-certified multifamily units when prevailing wages are not met.
The dwelling must be eligible for the ENERGY STAR Residential New Construction program and must be sold or leased to someone who will use it as a residence. The builder, not the buyer, claims the credit for the tax year the home was acquired.6Department of Energy. Section 45L Tax Credits for DOE Efficient New Homes A home doesn’t need separate ENERGY STAR certification to qualify for the higher-tier DOE credit; a builder can go straight for the $5,000 if the home meets the DOE program requirements.