Ask a residential builder what document their local building department wants alongside a Manual J load calculation, and REScheck usually comes up in the same breath. It's the residential counterpart to COMcheck — a free, DOE-developed tool that's become the de facto standard for demonstrating energy code compliance on single-family homes, townhomes, and low-rise multifamily buildings.
REScheck is software that checks a home's building envelope — insulation levels, window performance, air leakage assumptions, and related construction details — against the minimum requirements of the residential energy code adopted in a given jurisdiction, most often a version of the IECC's residential provisions.
Unlike Manual J (which calculates heating and cooling loads for equipment sizing), REScheck is strictly a code compliance tool. It answers a narrower, different question: does this home's envelope meet the code-required minimum energy performance, yes or no. The two tools are complementary, not interchangeable — a home can pass REScheck while still needing a completely separate Manual J for HVAC sizing.
REScheck primarily supports two compliance approaches:
Prescriptive compliance checks each building component (walls, ceiling, floor, windows, doors) individually against a fixed table of minimum R-values and U-factors for the applicable climate zone. Every component has to meet its individual minimum — there's no averaging.
Trade-off (UA) compliance allows some flexibility: if one assembly underperforms the prescriptive minimum, the home can still comply if other assemblies overperform enough to offset it, based on a total heat loss/gain comparison (UA — the sum of U-factor times area across all envelope components) rather than a component-by-component check. This is useful for designs with larger-than-typical window areas or unconventional wall assemblies that can't hit prescriptive minimums directly.
REScheck runs the comparison and produces a compliance certificate showing which method was used and how the numbers stack up.
Accuracy here matters — a REScheck report built on assumed rather than actual specified materials can pass on paper while the built home doesn't actually match what was submitted, which becomes a problem if a jurisdiction requires as-built verification.
Which IECC edition — and which specific amendments a state or local jurisdiction has layered on top of it — governs a given project varies considerably. Some states have adopted recent IECC cycles largely as-written; others use older editions or have significant local amendments (Florida, California, and Washington, for example, each run their own residential energy code programs layered on or replacing the base IECC framework, discussed separately). Confirming the correct code edition for the specific jurisdiction before running REScheck is a critical first step, since using the wrong edition produces a report reviewers won't accept.
REScheck isn't just for new construction. Additions and certain renovations that affect the building envelope often require compliance documentation too, though many jurisdictions apply somewhat different (often more lenient) standards to additions than to full new builds — worth confirming locally rather than assuming full new-construction requirements apply.
It's worth repeating because it's such a common point of confusion: REScheck confirms the envelope meets minimum code energy performance. Manual J calculates the actual heating and cooling load to size HVAC equipment correctly. A home can pass REScheck comfortably while still ending up with oversized HVAC equipment if Manual J wasn't done properly (or wasn't done at all) — they're separate, both-necessary steps in a complete, code-compliant project package.
Does every residential project need a REScheck report?
Most new construction and many additions/alterations do, though exact requirements depend on the jurisdiction and which residential energy code (and edition) has been adopted locally.
Is REScheck required in states with their own energy code, like California or Florida?
Not always in the standard federal form — states like California (Title 24) and Florida (R405/R402) run their own compliance software and forms specific to their state code, which serve the same function as REScheck but aren't literally REScheck. Washington's WSEC-R has its own compliance forms as well.
Can REScheck be used for additions?
Yes, though requirements for additions are often somewhat different from full new construction — confirm what your specific jurisdiction expects for the scope of work.
What's the difference between prescriptive and trade-off (UA) compliance in REScheck?
Prescriptive requires every individual envelope component to meet its own minimum. Trade-off compliance allows underperformance in one area if offset by overperformance elsewhere, based on total heat loss/gain across the envelope.
Psychro.Pro pairs REScheck-equivalent compliance documentation with Manual J load calculations, so your envelope compliance and HVAC sizing are handled together, not as separate scrambles. Learn more.
