The software will take any number you type. A recurring question on contractor forums is whether anyone downstream will notice. Here is who checks, when, and why the honest version of the same report is usually only one real change away.
Short answer: a REScheck with a window U-factor the window does not have will print "Passes." It will also put that number on a plan set a reviewer compares against your window schedule, on a house an inspector can read the NFRC label in, and on the permanent certificate the code requires you to post next to the furnace. The number does not stay in the software. And a report that fails by a few percent is almost always fixable with one legitimate input change, which is what the UA trade-off exists for.
REScheck is free, it runs in a browser, and it does not verify anything. Type 0.27 for the windows instead of the 0.32 on the label and the UA line goes green. The discussion thread that prompted this page put it plainly: you could get a bot to fill it in and "fiddle the window and door U-values and SHGC" until it passes.1 That is true. What the thread also worked through is that the software is the only place the number is not checked.
The plans examiner does not re-run your calculation. They compare the report to the drawings: the code edition and climate zone against the jurisdiction, the assemblies and R-values against the wall and roof sections, and the fenestration U-factor and SHGC against the window schedule. When a REScheck passes by a hair and the window schedule says "Low-E double pane" with no rating, the examiner asks for the manufacturer's certified value. If the schedule shows a 0.32 and the report says 0.27, that is a correction, not a conversation.
A report that shows where each number came from - "window U-factor 0.30 per manufacturer NFRC rating, window schedule sheet A-6" - gets through this step without a phone call. That is the only reason to annotate inputs, and it is why we do it.
The IECC requires fenestration U-factors to be determined by NFRC 100 testing and labeled and certified by the manufacturer (R303.1.3 in the 2015 through 2021 editions), and it requires insulation R-values to be marked on the product or identified by a certification (R303.1.1).2 Those labels exist so an inspector can read them. At the insulation inspection, the installed batt says R-13 or R-21 on its face. At framing or final, the NFRC sticker is on the glass. Many jurisdictions tell contractors to leave the window labels on until the inspector has seen them, for exactly this reason.
If the installed product does not match the approved report, the inspection fails and the envelope has to be brought up to what was approved - or a revised REScheck has to be submitted that passes with what was actually built. After drywall, the first option means opening walls; the second usually means better windows. Neither is cheaper than getting it right on paper.
The IECC requires a permanent certificate posted on or near the electrical panel or in the utility room, listing the predominant R-values of the insulation installed in the ceiling, walls, foundation, and ducts, the U-factor and SHGC of the fenestration, and the results of any duct and blower-door tests (R401.3 in the 2015 through 2021 editions).2 The numbers on a REScheck become the numbers on a sticker in the house. A future buyer's inspector, an energy auditor, or an appraiser doing an energy-efficient mortgage can read that certificate and read the window label six feet away.
A permit application is a signed statement to a government agency, and the model codes give the building official authority to suspend or revoke a permit "issued in error or on the basis of incorrect, inaccurate or incomplete information" (IRC R105.6 and the equivalent administrative provisions adopted in most states).3 A revoked permit stops work and can reach a certificate of occupancy already issued. Whether a knowingly false compliance document rises to a state-law misrepresentation or fraud claim depends on the state and the facts; it is not a question anyone wants to be the test case for over a window rating.
Where federal programs are involved the stakes are documented. In 2023 a Florida energy-rating firm agreed to pay $2.35 million to resolve federal allegations that it made false statements about its inspections and certifications of homes under EPA's ENERGY STAR program between 2014 and 2021.4 That was a certification program rather than a permit, and a rater rather than a contractor - but the mechanism was the same: energy performance numbers on paper that the houses did not have.
The reason people reach for the fudge is that the report fails by a little, and a little feels like it should not matter. The UA trade-off (the "UA alternative," IECC R402.1.5) was written for exactly that situation. It compares the total heat loss of your envelope against a code-minimum reference house, so any one component can miss its prescriptive value if another beats it.5 In practice a small failure comes back from one of these:
Every one of those is a change the drawings will show and the built house will back up. That is the difference between a trade-off and a fabrication: one survives inspection, the other depends on nobody looking.
Ask for a copy of the approved report. Compare the fenestration U-factor and SHGC to the NFRC labels on the windows that were actually delivered, and the ceiling and wall R-values to the insulation that went in. If they do not match, raise it before drywall closes - the permit is issued to your project and the certificate posted in your utility room carries those numbers. A second look from someone who reads these for a living costs less than a failed final.
Plan review compares them to the drawings. Inspection compares them to the labels on the installed product. The posted certificate carries them for the life of the house.
Correction and a failed inspection at minimum; the building official can revoke a permit issued on inaccurate information; state misrepresentation law can apply to a signed application.
Model the foundation you forgot, step the attic up one R-value, upgrade the worst windows, or replace default fenestration values with the real label. One of those almost always does it.
No. It is a compliance path written into the code. The inputs still have to be real; the trade-off is between real components.
This page describes how the model codes and the DOE tool work. It is not legal advice; whether a particular false statement is actionable depends on state law and the facts. Final authority rests with your building official.
Travis Smith, ICC-Certified Residential Energy Inspector / Plans Examiner. The same certification your building department's plan reviewer holds - working for you.