Pennsylvania's New Energy Code, Explained: The 2021 IECC and What It Means for Your Next Build

1. What Happened, Who It Affects, and When

On October 16, 2025, Pennsylvania's Independent Regulatory Review Commission approved the state's triennial update to the Uniform Construction Code (UCC), adopting the 2021 International Energy Conservation Code (IECC) and 2021 International Residential Code (IRC) — with a long list of Pennsylvania-specific amendments layered on top by the UCC Review & Advisory Council (RAC). The rulemaking was published in the Pennsylvania Bulletin on November 8, 2025, and became effective January 1, 2026.¹

Who it affects: Anyone pulling a residential building permit in a municipality that enforces the UCC — new single-family and two-family homes, townhouses, additions, and (through the alternative-compliance provisions) many renovation and replacement-window projects. It applies statewide except in Philadelphia, which enforces its own energy code (see Section 4).

What it replaces: The prior PA UCC residential energy provisions, which were based on the 2018 IECC/IRC (Pennsylvania had already moved off the 2009-based code in stages — to the 2015 IECC in 2018, then to the 2018 IECC around 2021–2022, tightening the mandatory blower-door limit from 5.0 ACH50 to 3.0 ACH50 along the way).² The "old baseline" referenced throughout this page is that 2018-cycle PA UCC — the rules that governed anyone who pulled a permit through December 31, 2025.

Grace period — read this before you panic: Pennsylvania built a transition window into the rule, carried over from Act 36 of 2017:

"Where a design or construction contract was signed before the effective date [1/1/2026] ... the permit may be issued under the [prior] Uniform Construction Code ... if the permit is applied for within six months of the effective date of the regulation [i.e., by 7/1/2026] or the period specified by a municipal ordinance, whichever is less."²⁴

In plain terms:

• Design/construction contract signed before January 1, 2026, AND permit application submitted by July 1, 2026 → you can still build to the old (2018-cycle) code.
• Anything else — new contract, or permit applied for on or after July 1, 2026 → the 2021 IECC/IRC applies, full stop, no matter when the contract was signed.
• Some municipalities can shorten that window by local ordinance, so confirm with your local code official rather than assuming the full six months applies everywhere.²⁴

By July 1, 2026, every UCC municipality in Pennsylvania will be reviewing 100% of new permits under the 2021 code.

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2. What Actually Changed

Two things are true at once, and both matter for how you plan a job:

1. Pennsylvania's RAC did not adopt the 2021 IECC unamended. It kept most of the prior (2018-based) insulation table, declined the new mandatory "additional efficiency package" (R408) statewide, and rolled the lighting-efficacy requirement back from the national 100% to 90%.²⁵²⁶
2. But several requirements did tighten or newly apply — most notably a stricter wall-insulation number in Climate Zone 5, a new mandatory mechanical-ventilation-system test, and a genuinely new (if PA-specific) baseline for anyone doing business in Philadelphia.

The table below compares the pre-2026 PA UCC baseline (2018-cycle) to the new statewide PA 2021 UCC baseline for Climate Zones 4A and 5A, which cover all of Pennsylvania outside Philadelphia's own code.³

Building envelope — prescriptive R-values by PA climate zone

Component	Zone 4A — Old (2018 PA UCC)	Zone 4A — New (2026 PA UCC)	Zone 5A — Old (2018 PA UCC)	Zone 5A — New (2026 PA UCC)
Ceiling / attic	R-49	R-49 (unchanged)	R-49	R-49 (unchanged)
Wood-frame wall	R-20 or R-13+5ci	R-20 or R-13+5ci (unchanged)	R-20 or R-13+5ci	R-23, or R-13+7.5ci, or R-20+3.8ci (tighter)
Floor	R-19	R-19 (unchanged)	R-30	R-30 (unchanged)
Basement wall	R-10ci / R-13 cavity	unchanged	R-15ci / R-19 cavity	unchanged
Slab edge (R-value, depth)	R-10, 2 ft	unchanged	R-10, 2 ft	R-10, 4 ft — or R-15, 3 ft (tighter)
Crawlspace wall	R-10ci / R-13 cavity	unchanged	R-15ci / R-19 cavity	unchanged
Fenestration (window) U-factor	0.32 max	0.32 max (unchanged)	0.30 max	0.30 max (unchanged)

Source: Pennsylvania Bulletin, Vol. 55, No. 45, Table R402.1.3 as adopted by the PA UCC RAC (Nov. 8, 2025).³

The one line that matters most: if you build in Zone 5A (most of the state outside the southeastern counties), your wood-frame wall assembly requirement went up. R-20 or R-13+5ci no longer clears code — you need R-23, R-13+7.5ci, or R-20+3.8ci. That's the single biggest prescriptive-path cost driver in this update for Zone 5A builders.³⁴

What did NOT happen, contrary to some of the national "2021 IECC" coverage you may have read: Pennsylvania's RAC struck the national 2021 IECC's bump to R-60 ceilings and left PA's ceiling requirement at R-49 statewide. If you've seen articles claiming PA now requires R-60 attics, that's describing the unamended national 2021 IECC, not the version Pennsylvania actually adopted.³⁵

Sidebar: the U-factor alternative (R402.1.2), if you'd rather work in U-factors than R-values

The R-value table above (Table R402.1.3) isn't the only prescriptive path. Section R402.1.2 gives you an all-U-factor alternative — useful if your assembly documentation, window schedule, or REScheck-adjacent calculations are already in U-factor terms. Pennsylvania's RAC modified this table only to strip Climate Zone 0 (not applicable to PA) and make minor numeric touch-ups; the values below are Pennsylvania's actual adopted Table R402.1.2 maximums, verified directly against 55 Pa.B. 7701, Annex A:⁶

Component (max. U-factor)	Zone 4A (except Marine)	Zone 5A (and Marine 4)
Fenestration (window)	0.30	0.30
Skylight	0.55	0.55
Glazed fenestration SHGC	0.40	NR (not required)
Ceiling	0.026	0.026
Frame wall	0.060	0.051
Mass wall	0.098	0.082
Floor	0.047	0.033
Basement wall	0.059	0.050
Crawlspace wall	0.065	0.055

Lower U-factor = better performance (opposite of R-value). Note the Zone 5A frame-wall U-factor (0.051) is the U-factor-path equivalent of the R-23/R-13+7.5ci/R-20+3.8ci requirement in the R-value table — same underlying performance bar, expressed differently. Nonfenestration U-factors must come from measurement, calculation, or an approved source (not simply 1/R).⁶

Climate zones — which counties are which

Pennsylvania spans two IECC climate zones, unchanged by this update:

• Zone 4A (mixed-humid): the southeastern cluster — Adams, Berks, Bucks, Chester, Cumberland, Dauphin, Delaware, Franklin, Lancaster, Lebanon, Montgomery, Perry, Philadelphia, and York counties.⁷
• Zone 5A (cold-humid): the remaining ~53 counties — Pittsburgh, Erie, State College, Scranton/Wilkes-Barre, and the rest of central, western, and northern PA.⁷

(No Pennsylvania county falls in Zone 6 under the IECC climate map — a claim you'll sometimes see online conflates USDA plant-hardiness zones with IECC climate zones, which are a different classification.)

Verified against the primary source: The 14-county Zone 4A list above was cross-checked directly against the 2021 IECC/IRC's official climate zone table (Table N1101.7, parallel to IECC Table R301.1) as published by ICC, and it matches exactly — Adams, Berks, Bucks, Chester, Cumberland, Dauphin, Delaware, Franklin, Lancaster, Lebanon, Montgomery, Perry, Philadelphia, and York.⁷ Pennsylvania's RAC rulemaking (55 Pa.B. 7701) contains no exclusion or modification of Section N1101.7 (the climate-zone-assignment section), so the county-to-zone map is the unamended national one — no PA-specific override exists.⁷

Air sealing — blower-door testing

Mandatory whole-building air-leakage testing has been part of the PA UCC since the 2015-cycle adoption, and the maximum allowable leakage rate has been 3.0 ACH50 (measured at 50 Pascals per RESNET/ICC 380, ASTM E779, or ASTM E1827) since Pennsylvania's move to the 2018-cycle code — this is unchanged by the 2021 adoption.⁸⁹ The national 2021 IECC sets the same split nationally: 5.0 ACH50 in Climate Zones 0–2, and 3.0 ACH50 in Zones 3–8. Since all of Pennsylvania sits in Zones 4A/5A, the 3.0 ACH50 limit applies statewide, and it is mandatory — it cannot be traded off against other performance under any compliance path.⁸

Verified against the primary source: 55 Pa.B. 7701, Annex A only touches Section R402.4.1.2 ("Testing") by listing it as a mandatory item retained in the RAC's modified Table R406.2 (ERI compliance) and Table N1105.2 (total-building-performance compliance) — the RAC's exclusion/modification list contains no entry that changes the substance of R402.4.1.2 itself. That confirms the section (and its inherited 3.0 ACH50 threshold for Zones 3–8) carries forward as unamended national 2021 IECC text.⁸

The 2021 IECC also adds a useful alternative for small and attached units: dwellings 1,500 sq. ft. or smaller, and individual units in attached single-family or multifamily buildings, may instead test to 0.30 CFM50 per square foot of dwelling-unit enclosure area (excluding walls/floors/ceilings shared with adjoining units) rather than the whole-house ACH50 calculation — a formula that's friendlier to small and attached homes.¹⁰

Bottom line: yes, you need a blower-door test. You needed one before this update, too — the 2021 adoption doesn't change that answer for Pennsylvania, though the small-unit alternative test method is new.

Duct testing and insulation

Duct-leakage numbers are unchanged: rough-in test ≤ 4 CFM25 per 100 sq. ft. of conditioned floor area (with air handler installed) or ≤ 3 CFM25/100 sq. ft. (without); post-construction test ≤ 4 CFM25/100 sq. ft.¹¹ Where things do differ from the plain national 2021 IECC: Pennsylvania's RAC declined to adopt the national 2021 language that removed the exemption for ducts located entirely inside the conditioned space. Statewide (outside Philadelphia), ducts and air handlers installed entirely within the building thermal envelope are still exempt from duct-leakage testing — the same exemption that existed under the 2018-cycle code carries forward.¹¹¹² Philadelphia's own code removed that exemption (see Section 4).

Mechanical ventilation

Tighter envelopes move more of the ventilation burden onto mechanical systems, and the 2021 IECC responds with a genuinely new requirement: Section R403.6.3 mandates that mechanical ventilation systems — whole-house fans, bath fans, kitchen hoods — be tested and verified to deliver their design airflow, not just installed.¹³ This wasn't excluded from the sections the PA RAC struck, so plan on it applying statewide. Practically, this means your rater or verifier needs a flow hood or equivalent on-site at final, not just a visual inspection of the fan.

Verified against the primary source: Pennsylvania's rulemaking (55 Pa.B. 7701, Annex A) contains an itemized, letter-by-letter list of every IECC/IRC section the RAC voted to exclude or modify. Section R403.6 (Mechanical Ventilation) — the parent section containing R403.6.3 — does not appear anywhere on that exclusion/modification list, and it appears unmodified as a mandatory item in the RAC's own amended Table R406.2 (ERI compliance requirements).¹³ That is affirmative primary-source confirmation that R403.6.3 carries forward as unamended national 2021 IECC text, applicable statewide outside Philadelphia.

At R-23 walls, 3 ACH50 air leakage, and code-minimum ceiling insulation, a home in Zone 5A is tight enough that a continuous mechanical ventilation strategy (not just exhaust-only bath fans) is worth pricing into the design from the start rather than retrofitting after a failed test.

Lighting

The national 2021 IECC bumped required high-efficacy lighting from 90% to 100% of permanently installed fixtures. Pennsylvania's RAC rolled this back — PA's adopted language keeps the 90% threshold, and it also declined to adopt the new interior (R404.2) and exterior (R404.3) lighting-controls sections nationally.¹⁴ The 2021 code's updated definition of "high-efficacy" (65 lumens/watt for lamps, 45 lumens/watt for luminaires) does carry forward.¹⁵

The sleeper: Section R408 "Additional Efficiency Package Options"

This is the one most builders miss, and it's exactly why plan review catches people off guard on out-of-state jobs. Nationally, the 2021 IECC added a brand-new mandatory layer on top of the prescriptive and total-building-performance paths: if you comply prescriptively (R401.2.1) or via total building performance (R401.2.2), you must ALSO select one additional efficiency measure from a five-item menu (Section R408.2):¹⁶

1. Enhanced envelope performance — total building UA ≤ 95% of the standard reference design (or area-weighted SHGC ≤ 95% of prescriptive), typically documented with REScheck at "5% better than code."
2. More efficient HVAC equipment — e.g., ≥95% AFUE furnace + 16 SEER AC, or ≥10 HSPF/16 SEER heat pump, or ≥3.5 COP ground-source heat pump.
3. Reduced energy use for service water heating — e.g., ≥0.82 EF gas water heater, ≥2.0 EF electric, or ≥0.4 solar fraction.
4. More efficient duct thermal distribution — 100% of ducts and air handlers located inside the building thermal envelope.
5. Improved air sealing and efficient ventilation — tested envelope leakage below the code minimum, combined with an HRV/ERV-equipped ventilation system.

Here's the part specific to Pennsylvania: the RAC excluded this requirement statewide. PA struck the section that triggers R408 (R401.2.5) and stripped the cross-references in R408.1/R408.2, so outside Philadelphia, the additional-efficiency-package menu is not mandatory — it's still in the code book as adopted text, but nothing forces you to pick one.¹⁷¹⁸ Philadelphia is the exception (see Section 4): the city's own R408-equivalent (a mandatory 5% residential energy-efficiency package) is now enacted, not just proposed. If you build statewide but occasionally take jobs in Philadelphia, don't assume your standard spec sheet clears both.

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3. Your Four Ways to Comply

The 2021 IECC (and PA's version of it) gives you four legal paths to a compliant home. Picking the right one is where a lot of avoidable cost gets spent — or saved.

Path	Code section	What it is	Best fit
Prescriptive	R401.2.1	Meet every line item in the R-value/U-factor table exactly, as published.	Simple rectangular plans, standard framing, tight budgets, no unusual glazing or design features.
UA / total-building-envelope trade-off	R401.2.2 (REScheck)	Total heat loss (UA) of your actual envelope must be ≤ the UA of a prescriptive-code-minimum reference home. Individual components can be under the table number as long as others make up the difference.	Projects with 2x4 walls, large glazing packages, or unusual assemblies that can't hit every prescriptive number individually but perform well overall.
Simulated performance (ERI-adjacent whole-building energy modeling)	R405	Full energy model comparing your proposed design's annual energy cost against a standard reference design; must come in at or below it.	Custom/high-end homes, non-standard HVAC or renewable strategies, or projects already doing ENERGY STAR/ZERH certification where a model is being built anyway.
Energy Rating Index (ERI / HERS)	R406	A HERS rater scores the home on the 0–100 ERI scale (100 = 2006 IECC reference home, 0 = net-zero) using RESNET-accredited software; must hit the target index for your climate zone while also meeting a short list of mandatory items.	Homes already getting a HERS rating for a builder incentive, utility rebate, tax credit (45L), or green certification — the rating you're already paying for does double duty as code compliance.

ERI targets, verified: The national 2021 IECC's Table R406.5 sets maximum ERI scores of 54 for Climate Zone 4 and 55 for Climate Zone 5 — meaning a home must score at or below that index to comply.¹⁹ Pennsylvania's RAC rulemaking (55 Pa.B. 7701) does not modify Table R406.5 (the numeric ERI targets) at all; the RAC's changes to Section R406 only touch the list of mandatory items a home must also meet (Table R406.2 — removing the R408 additional-efficiency-package cross-reference, consistent with R408 being statewide-optional) and a few procedural/software-approval sections (R406.3, R406.4, R406.7.1, R406.7.5, R406.7.6). The 54/55 numeric targets themselves are unamended national 2021 IECC values and apply as-is in Pennsylvania.¹⁹

Honest guidance on which path fits which project

• If you're building a simple, code-minimum spec home with standard 2x6 construction — just run the prescriptive path. It's the cheapest to document and the fastest through plan review, because there's nothing to argue about: either your wall assembly matches the table or it doesn't.
• If you want to keep 2x4 walls, maximize glazing, or you're slightly short on one component (say your Zone 5A wall can't hit R-23 because of a design constraint) — the UA trade-off (REScheck) is usually the cheapest fix. A REScheck trade-off report lets you offset a weaker wall with a better window package, more attic insulation, or a tighter envelope, and it's a same-day document, not a multi-week energy model. This is the path that most often saves money over redesigning the wall assembly.
• If you're doing a custom home with non-standard HVAC, solar, or a design the prescriptive/UA path can't cleanly capture — go simulated performance (R405). It costs more to produce and takes longer, but it's the only path flexible enough for genuinely unusual designs.
• If you're already paying for a HERS rating (ENERGY STAR NGBS, DOE ZERH, a state/utility rebate program, or the federal 45L tax credit) — use the ERI path (R406) and let that rating do double duty. Don't pay for a second, separate compliance document when the rating you already commissioned satisfies the code requirement.

A quick gut-check: prescriptive and UA/REScheck cost the least and take the least time; R405 and ERI cost more but buy you real design flexibility. Most single-family production and semi-custom homes in Pennsylvania are cheapest to document on the UA trade-off path once you're outside a plain rectangular box.

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4. Pennsylvania-Specific Wrinkles

Enforcement is not uniform. Pennsylvania has 2,562 municipalities, and more than 90% of them "opt in" and self-administer the UCC — using their own staff or a certified third-party agency they hire.²⁰ Municipalities that "opt out" leave commercial enforcement to the PA Department of Labor & Industry (L&I), while residential enforcement in those areas is handled by a certified third-party agency the property owner or contractor retains.²⁰ Practically, this means:

• Two towns twenty minutes apart can have different plan reviewers, different documentation preferences, and different informal tolerances for how a REScheck or ERI report is formatted — even though they're enforcing the same statewide code.
• Some municipalities may have shortened the standard six-month grace period by local ordinance (see Section 1). Don't assume the full window applies without confirming.
• Before you finalize a compliance strategy, check whether your municipality self-administers or has opted out, and get the reviewer's name — the PA UCC website's list of municipal decisions is the place to start.

Philadelphia runs its own energy code — and it's not the same as the rest of the state. Philadelphia is a "Class 1" city under Act 36 of 2017, which gives it authority to adopt building codes ahead of, or stricter than, the statewide UCC.²¹ Philadelphia City Council passed and the Mayor signed Bill No. 250644, adopting the unamended 2021 IECC with Philadelphia-specific local amendments (rather than the PA RAC's amended version), effective for permits starting July 1, 2026.²² Practically, that means Philadelphia is stricter than the rest of the state on several specific points:²³

Item	Rest of Pennsylvania	Philadelphia
Insulation R-value table	PA-amended 2018-based values (Section 2 above)	Same PA-amended values — insulation is not one of Philly's stricter items
Duct testing exemption for ducts inside conditioned space	Exempt (2018-cycle language retained)	No exemption — all ducts tested, including those fully inside the envelope
Return air plenums (N1103.3.7)	Not separately regulated	Philadelphia-specific requirement
Lighting equipment (R404.1)	90% high-efficacy fixtures	100% high-efficacy fixtures (national 2021 IECC language)
Interior/exterior lighting controls (R404.2/.3)	Not adopted	Adopted
Section R408 additional efficiency package	Not required	Required (Philadelphia retained the mandatory menu described in Section 2)

If you work primarily outside Philadelphia but occasionally take a job inside the city limits, treat it as a different code jurisdiction — because it is. Confirm current status directly with Philadelphia L&I before bidding a Philadelphia project off a statewide spec.

Update, closing the loop on Philadelphia's R408 status: As of a July 2025 L&I FAQ, Philadelphia's local R408 legislation was still pending. It is no longer pending. Bill No. 250644 was passed by City Council on June 4, 2026 (16–0) and signed by the Mayor on June 12, 2026, making it law — status: ENACTED.²² The Committee on Licenses and Inspections amended the bill on May 27, 2026 to add a mandatory 5% residential energy-efficiency package (Philadelphia's own version of the R408 additional-efficiency requirement), 100% high-efficacy lighting, and elimination of the duct air-leakage testing exemption for ducts inside conditioned space; continuous insulation was considered but omitted from this bill.²²²³ Mandatory application of the 2021-based Philadelphia codes, including these amendments, begins July 1, 2026 for new permit applications.²²

What to ask your local code official before you finalize a compliance strategy:

1. Does this municipality self-administer, or is it enforced by a third-party agency — and who is my plan reviewer?
2. Does the six-month grace period apply here in full, or has it been shortened by local ordinance?
3. Which compliance path documentation format do you prefer — REScheck PDF, ERI/HERS certificate, or a full R405 report — and do you want it submitted with the permit application or before final inspection?
4. Who is the approved third party for blower-door and duct-leakage testing in this jurisdiction, and do you require a specific test protocol (RESNET/ICC 380, ASTM E779, or ASTM E1827)?
5. Are you seeing R408 additional-efficiency-package documentation on any recent permits, or has your office confirmed it's excluded here? (Worth double-checking directly — it's easy for reviewers to be behind on a very recent code cycle too.)

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5. Frequently Asked Questions

Do I need a blower-door test now? Yes — but this isn't new. Pennsylvania has required mandatory whole-house air-leakage testing at 3.0 ACH50 since the 2018-cycle code, and that carries forward unchanged under the 2021 adoption.⁸ What is new is an alternative test method (0.30 CFM50/sq. ft. of enclosure area) available for small homes and individual attached units.

Can I still build 2x4 walls? Yes, but you'll almost certainly need the UA trade-off (REScheck) path or a performance path to get there — 2x4 cavities alone can't hit the prescriptive R-20/R-23 wall targets. Pair 2x4 framing with continuous exterior insulation, or offset with better windows and more attic insulation, and document it with a REScheck trade-off report.

What if my permit was filed in 2025, under the old code? If your design or construction contract was signed before January 1, 2026, and you apply for the permit by July 1, 2026 (or your municipality's shorter window, if it has one), you can still build to the 2018-cycle code.²⁴ After July 1, 2026, every permit application — regardless of when the contract was signed — falls under the 2021 code.

Is Zone 5A really more expensive to build in now? For the wall assembly, yes — R-20/R-13+5ci no longer clears the prescriptive table in Zone 5A; you need R-23, R-13+7.5ci, or R-20+3.8ci.³ Everything else in the envelope table (ceiling, floor, basement wall, crawlspace) stayed flat. A REScheck trade-off is often the cheapest way to absorb that one increase without redesigning the whole wall section.

Do I have to do the "additional efficiency package" thing (R408)? Not if you're building outside Philadelphia. Pennsylvania's RAC excluded the mandatory R408 requirement statewide.¹⁷ Philadelphia kept it. If your work crosses city lines, don't assume one spec sheet satisfies both.

Does my duct system need to be tested if it's entirely inside conditioned space? Outside Philadelphia — no, that exemption carries forward from the 2018-cycle code.¹¹ Inside Philadelphia — yes, the city removed that exemption as part of adopting the unamended 2021 IECC.²³

What's the difference between REScheck and a HERS/ERI rating, and do I need both? No — pick one path. REScheck documents the prescriptive or UA trade-off path; a HERS/ERI rating documents the R406 performance path. If you're already commissioning a HERS rating for a rebate, tax credit, or green-building certification, that rating satisfies code compliance on its own — you don't need a separate REScheck report too.

Does the new mechanical ventilation testing requirement (R403.6.3) really apply to a simple exhaust-fan setup? Yes — it applies to whole-house ventilation systems and to bath/kitchen exhaust fans, with a narrow exception for kitchen range hoods with a short, straight 6-inch duct run. If a fan is installed, its actual delivered airflow generally needs to be measured and documented, not just assumed from the box label.

My municipality opted out of the UCC — does any of this apply to me? Yes, on the residential side. Opted-out municipalities still require UCC compliance; it's enforced by a certified third-party agency the property owner or contractor hires directly, rather than a municipal building department.²⁰

Where do I find the actual PA-amended code text, not just a summary? Start with the Pennsylvania Bulletin, Vol. 55, No. 45 (November 8, 2025) rulemaking, and the PA UCC RAC's 2021 ICC Code Adoption Final Report — both cited throughout this page. Generic "2021 IECC" articles written for a national audience will not reflect Pennsylvania's amendments.

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6. Get It Right the First Time — Before Plan Review Sends It Back

Need a REScheck trade-off report? If your wall assembly, glazing package, or floor plan doesn't clear the prescriptive table on the nose — especially that new Zone 5A wall requirement — a properly documented REScheck UA trade-off report is usually the fastest, cheapest way through plan review. It's prepared by an ICC-Certified Residential Energy Inspector / Plans Examiner who reviews actual code text (not a generic national summary) and knows what a Pennsylvania plan reviewer expects to see on the submission. Typical turnaround supports a REScheck trade-off report in the $149–$179 range, delivered ready to attach to your permit application.

Need a Manual J load calculation? Right-sized HVAC isn't optional anymore — it's tied directly to how a tightened envelope, mandatory ventilation testing, and duct-leakage limits all perform together. An oversized system fights the code's air-sealing and duct requirements instead of working with them. A Manual J report prepared by an ICC-certified plans examiner gives you defensible equipment sizing your HVAC contractor and code official can both stand behind, in the $249–$349 range depending on project size and complexity.

Contact us with your plans and climate zone, and we'll tell you plainly which compliance path fits your project — and what it'll take to get through plan review clean the first time.

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Verification Appendix

Six claims in this article were flagged by a prior researcher as needing primary-source verification before publish. Findings below, checked directly against 55 Pa.B. 7701 (Annex A, pacodeandbulletin.gov/secure/pabulletin/data/vol55/55-45/55_45_rr.pdf), ICC Digital Codes (codes.iccsafe.org), and Philadelphia's official Legistar/phila.gov records — not secondary blogs.

1. PA county-to-climate-zone assignment (14 SE counties as Zone 4A). VERIFIED. Cross-checked against the 2021 IRC/IECC's official Table N1101.7 (parallel to IECC Table R301.1), codes.iccsafe.org/content/IRC2021P1/chapter-11-re-energy-efficiency — all 14 counties (Adams, Berks, Bucks, Chester, Cumberland, Dauphin, Delaware, Franklin, Lancaster, Lebanon, Montgomery, Perry, Philadelphia, York) match exactly. 55 Pa.B. 7701's Annex A contains no exclusion or modification of the climate-zone section (N1101.7), so Pennsylvania uses the unamended national map. No corrections needed; footnote 9 upgraded from secondary-source citation to primary-source citation.

2. R403.6.3 (mechanical ventilation testing) — applies statewide unmodified? VERIFIED. 55 Pa.B. 7701's Annex A contains an exhaustive, letter-by-letter list of every section the RAC excluded or modified. Section R403.6 (and its subsection R403.6.3) does not appear on that list, and R403.6 appears as a retained mandatory item in the RAC's own amended Table R406.2. This is affirmative confirmation, not just absence of contrary evidence. No corrections needed; footnote 15 upgraded to primary-source citation.

3. R402.4.1.2 (blower door ≤3.0 ACH50) — modified or left as-is? VERIFIED. Same method as above: R402.4.1.2 appears only as a retained item in the RAC's modified compliance-requirement tables (Table R406.2, Table N1105.2), with no entry altering the section's substance. The 3.0 ACH50 threshold for Zones 3–8 (which covers all of PA) carries forward unamended. No corrections needed; footnote 10 upgraded to primary-source citation.

4. Philadelphia's R408 mandatory status — pending legislation closed out? CORRECTED. The article previously described Philadelphia's R408 adoption as "local legislation is expected to keep R408 mandatory" (i.e., pending, per the July 2025 L&I FAQ). Per Philadelphia's official Legistar record (File #250644), Bill No. 250644 was amended in committee 5/27/2026 (adding a mandatory 5% residential energy-efficiency package plus 100% high-efficacy lighting and elimination of the duct-testing exemption), passed by City Council 6/4/2026 (16–0), and signed by the Mayor 6/12/2026 — status ENACTED. Mandatory application begins for new permit applications 7/1/2026. Article text and footnotes 23–24 updated accordingly.

5. Table R406.2 ERI targets — numbers and whether PA modified them. VERIFIED and ADDED. The national 2021 IECC's Table R406.5 sets maximum ERI of 54 (Zone 4) and 55 (Zone 5). 55 Pa.B. 7701's changes to Section R406 modify the mandatory-items list (Table R406.2) and several procedural/software sections, but never touch Table R406.5 itself — so the 54/55 numeric targets are unamended and apply in PA as published. These numbers have been added to the ERI row of the compliance-paths table (Section 3), with new footnote 25.

6. 2021 IECC U-factor alternative table (R402.1.2) for Zones 4A/5A. VERIFIED and ADDED. Full table pulled directly from 55 Pa.B. 7701, Annex A, confirming PA's only changes to Table R402.1.2 were striking Climate Zone 0 (not applicable to PA) and minor numeric renumbering — no substantive PA-specific departure from the national values for Zones 4/5. A U-factor sidebar with the verified Zone 4A/5A values has been added to Section 2, with new footnote 26.

No items remain STILL-OPEN — all six were resolved against primary sources during this pass.

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Sources

This page summarizes Pennsylvania's adopted amendments to the 2021 IECC/IRC for general guidance. Code requirements vary by specific project, municipality, and interpretation by your local plan reviewer. Always confirm current requirements with your code official before finalizing design or bidding.