REScheck Requirements (2026): R-Values, Window U-Factors, Climate Zones, and What You Need for a Building Permit
By Brad Buzzell, M.Ed., RESNET-certified HERS Rater · Last reviewed September 28, 2026
REScheck requirements are set by the energy code your jurisdiction has adopted, not by REScheck itself. To pass, your home's walls, ceilings, floors, foundation, windows and doors have to meet that code's insulation R-values and U-factors for your climate zone, either component by component or through REScheck's UA trade-off. You also have to meet the code's mandatory items, like air-sealing and duct testing. Under the unamended 2021 IECC for example, a Climate Zone 4 home needs R-60 in the ceiling and windows at U-0.30 or better.
I've been doing energy code compliance for more than 25 years, and the question I get most often is some version of "what do I need to pass REScheck?" The honest answer is that it depends on where the house is. But "it depends" isn't very useful when you're trying to get a permit, so this guide gives you the actual numbers, the information you need to gather, and the mistakes that cause most failed reports.
What REScheck Is (in One Paragraph)
REScheck is free residential energy code compliance software from the U.S. Department of Energy's Building Energy Codes Program. You enter the areas and insulation levels of the building envelope, pick the code your jurisdiction uses, and REScheck calculates whether the house complies. It's used for new homes, additions, alterations, and low-rise multifamily buildings (three stories or less above grade). Commercial buildings use COMcheck instead. For the longer explanation, see What Is a REScheck?
Step One: Figure Out Which Energy Code Applies
This is where more REScheck problems start than anywhere else. The newest code in the software is not automatically the code you use. States and cities adopt energy codes on their own schedule, often with amendments, so two projects fifty miles apart can be under different editions.
Before anything gets entered into REScheck, pin down:
The project address (including county, since that sets the climate zone)
The adopted code and edition (for example, 2018 IECC, 2021 IECC, or a state code like the Vermont RBES)
Any state or local amendments
The effective date, which usually ties to your permit application date
The project type: new construction, addition, or alteration
To look up your state quickly, use our State IECC Code Checker or browse REScheck requirements by state. DOE also tracks adoption on its residential code adoption status page. If there's any doubt, call the building department. That five-minute call can save you a rejected report.
REScheck Insulation and Window Requirements by Climate Zone (2021 IECC)
The 2021 IECC is the most widely referenced residential code right now, so here are its prescriptive values. If every component meets these, the envelope complies without any trade-offs. If one component falls short, REScheck's UA trade-off may still get you there (more on that below).
How to read this: "13+5ci" means R-13 cavity insulation plus R-5 continuous insulation. "NR" means no requirement. Many states amend these values, so always confirm against the code your jurisdiction adopted. Mass wall values and table footnotes are omitted for space.
The same requirements in plain text (2021 IECC, unamended):
Climate Zones 0–1: R-30 ceiling, R-13 walls, R-13 floors, SHGC 0.25, no prescriptive window U-factor (0.50 max)
Climate Zone 2: R-49 ceiling, R-13 walls, R-13 floors, U-0.40 windows, SHGC 0.25
Climate Zone 3: R-49 ceiling, R-20 walls (or R-13 + R-5ci), R-19 floors, R-5ci or R-13 basement walls, R-10 slab edge 2 ft deep, U-0.30 windows, SHGC 0.25
Climate Zone 4 (except Marine): R-60 ceiling, R-30 walls (or R-20 + R-5ci, or R-13 + R-10ci), R-19 floors, R-10ci or R-13 basement walls, R-10 slab edge 4 ft deep, U-0.30 windows, SHGC 0.40
Climate Zone 5 and Marine 4: R-60 ceiling, R-30 walls (or R-20 + R-5ci), R-30 floors, R-15ci or R-19 basement walls, R-10 slab edge 4 ft deep, U-0.30 windows, SHGC 0.40
Climate Zones 6–8: R-60 ceiling, R-30 walls (or R-20 + R-5ci), R-30 floors (R-38 in Zones 7–8), R-15ci or R-19 basement walls, R-10 slab edge 4 ft deep, U-0.30 windows, no SHGC requirement
Quick example: A new home in Climate Zone 5 (which covers much of Ohio, Indiana and Pennsylvania) under the unamended 2021 IECC would need R-60 in the attic, R-30 cavity walls (or R-20 plus R-5 continuous), R-30 floors over unconditioned space, and U-0.30 windows. Ohio's adopted residential code has its own amendments, though, which is exactly why you verify the code first.
What about the 2024 IECC?
REScheck-Web supports the 2024 IECC, including the Appendix RG stretch code. The 2024 edition changes some fenestration values and adds a requirement in Section R408 that most new homes earn additional energy efficiency credits. DOE's analysis describes this as 10 credits from at least two measures. So on a 2024 project, meeting the insulation table alone isn't the whole job. Our REScheck and the 2024 IECC article breaks down the R408 credits and Appendix RG.
How REScheck Decides Pass or Fail
REScheck-Web gives you a few ways to show compliance, depending on the code:
Prescriptive: every component meets or beats the table value. Simple, but zero flexibility.
UA trade-off: the one most people use. REScheck multiplies each component's U-factor by its area (U × A) and adds them up. If your house's total UA is at or below the UA of the same house built exactly to code, you pass.
Performance alternative: available for some codes, based on annual energy use rather than envelope heat loss.
The UA trade-off is why REScheck works so well for real houses. Say your walls come in a little under the table because of the framing you're using. Better windows or extra attic insulation can make up the difference, as long as the total works out. That's also why "will R-19 walls pass?" doesn't have a yes-or-no answer. It depends on everything else in the house.
For the math behind it, see UA Trade-Off in REScheck: A Simplified Explanation.
Passing the Calculation Isn't Everything: Mandatory Requirements
This part gets skipped a lot. A REScheck report has two pieces: the compliance certificate (the envelope calculation) and the inspection checklist. The checklist lists mandatory code requirements that apply no matter how well the UA calculation turns out. Under the 2021 IECC, those include:
Air leakage testing (blower door): generally 5.0 ACH50 or less in Climate Zones 0–2 and 3.0 ACH50 or less in Zones 3–8
Duct leakage testing when ducts are outside the conditioned space
Air sealing at the specific locations the code lists (rim joists, penetrations, top plates, and so on)
Programmable thermostat and duct and pipe insulation
High-efficacy lighting
Mechanical ventilation
An energy certificate posted at the electrical panel
A house can pass REScheck on paper and still fail final inspection on a blower door test. As a HERS rater, that's the gap I'd want every builder to know about before drywall goes up.
What Information You Need for a REScheck
A REScheck is only as good as what goes into it. The best source is a complete plan set: floor plans, elevations, wall sections, foundation plan, and window and door schedules. Here's the checklist:
Project: full address with county, project type (new, addition, or alteration), and the adopted code if you know it
Building: conditioned floor area, number of stories, ceiling heights, and exterior wall dimensions
Insulation: R-values for the ceiling, walls (cavity and continuous listed separately), floors, basement or crawlspace walls, and slab edge
Windows and doors: area, NFRC U-factor, and SHGC for each type, plus door U-factors
Anything else: building department comments, nonstandard wall systems (SIPs, ICF, double-stud), and for additions, which part is new
"Energy-efficient windows" on a plan note isn't enough. I need the actual U-factor and SHGC from the NFRC label or the manufacturer's spec sheet. Missing window specs are the single most common reason an order gets held up. The full list is in What Information Do You Need to Order a REScheck?
R-Value Details That Trip People Up
Enter insulation R-value only, not the whole wall
REScheck's standard wall assemblies already account for drywall, sheathing, air films and siding. Enter only the insulation R-value. Adding the other layers on top double-counts them.
Cavity vs. continuous insulation
Cavity insulation sits between the studs (batts, blown-in, spray foam). Continuous insulation (ci) runs unbroken over the framing, usually rigid foam or insulated sheathing, and it cuts thermal bridging through the studs. REScheck has separate fields for each, and mixing them up is one of the most common input errors I see.
Compression isn't calculated
REScheck uses nominal R-values. If you enter R-19 cavity insulation, it's treated as R-19 even if the batt gets compressed into a 2x4 wall. The software won't flag that, so it's on the designer to specify it correctly.
Nonstandard walls need an assembly U-factor
SIPs, ICF, double-stud walls, and other custom assemblies go in REScheck's "Other" wall category, which asks for a whole-assembly U-factor rather than an R-value. You get that number from the manufacturer or a calculation. You can't just add up the R-values.
Window U-factor and SHGC
U-factor is how fast heat moves through the window, and lower is better. SHGC (solar heat gain coefficient) is how much solar heat gets through, and it matters most in the south. Under the 2021 IECC, Zones 0–3 require SHGC of 0.25 or less and Zones 4–5 require 0.40 or less. Always use the NFRC-rated whole-window values, not center-of-glass numbers.
REScheck for Additions, Remodels, and Special Cases
Additions
Additions are entered like new construction, but per DOE, only the new portion needs to be modeled. You don't have to bring the whole existing house up to code. REScheck can trade off between the addition's components.
Alterations and remodels
For alterations, each component you're changing is identified individually. Some qualify for exemptions (for example, existing wall cavities that aren't being opened up), and the rest get their new insulation and window values entered. The exact scope of work matters a lot here, so describe it clearly when you order.
Garage conversions
Turning a garage into living space moves the thermal boundary. The questions that decide how it's modeled: Which walls are now exterior to conditioned space? Is the slab being insulated? Is the ceiling insulated? Are you adding windows? Depending on the jurisdiction, it may be treated as an addition or as an alteration.
Basements and crawlspaces
For basements, REScheck needs the wall height, depth below grade, and how far down the insulation goes. For crawlspaces, the key question is whether you're insulating the crawlspace walls (a conditioned crawl) or the floor above it (a vented crawl). Those are different assemblies with different requirements.
Top Reasons a REScheck Fails, and How to Fix It
Wrong code or edition selected. Fix: verify the adopted code before you start.
Wrong climate zone from a bad address or county. Fix: use the full project address.
Window specs missing or wrong. Fix: use NFRC-labeled U-factor and SHGC.
Cavity and continuous insulation mixed up. Fix: enter them in their own fields.
Wall areas wrong, with window and door openings not deducted properly. Fix: take dimensions from the plans.
Foundation entered as the wrong type (slab vs. basement vs. crawl). Fix: match the foundation plan.
Custom walls entered as standard assemblies. Fix: use the "Other" category with an assembly U-factor.
If the inputs are right and the house still fails, the usual fixes, roughly in order of cost-effectiveness, are: more attic insulation, better windows (often the biggest lever if there's a lot of glass), adding continuous wall insulation, and improving floor or foundation insulation. REScheck will show you which component is dragging the total down. Failing doesn't mean the design can't be built. It means the envelope needs adjusting. For help reading the results, see how to interpret a REScheck report.
REScheck vs. Manual J vs. Manual S vs. COMcheck
In short: REScheck shows the envelope meets the energy code. A Manual J calculates heating and cooling loads. A Manual S confirms the equipment fits those loads. COMcheck is the commercial version of REScheck, used for commercial buildings and residential buildings four or more stories tall.
REScheck doesn't size HVAC, and a Manual J doesn't show code compliance. Many jurisdictions want both. See the full comparison in REScheck vs. Manual J vs. COMcheck.
When You Don't Use REScheck
Not every jurisdiction accepts REScheck. California uses its own Title 24 compliance software, and some states and cities require their own forms or a performance path like a HERS/ERI report instead. If your building department hands you a state-specific form, that's what they want. Our state-by-state pages note where that applies, including Florida, Michigan, and Alabama.
REScheck-Web vs. REScheck Desktop
Use REScheck-Web. DOE states that REScheck Desktop only supports compliance through the 2015 IECC. The 2018, 2021, and 2024 IECC, plus newer state codes, are only in REScheck-Web. As of version 4.2.0 (October 2025), REScheck-Web supports the 2009 through 2024 IECC, 2024 IECC Appendix RG, the 2021 Louisiana code, and the 2024 Vermont RBES. New to the software? Start with our REScheck-Web Beginner's Guide.
How Much a REScheck Costs and How Long It Takes
REScheck is free software, but most builders and homeowners pay a professional to prepare the report so it's right the first time and holds up at plan review. At Rescheck Review, pricing is based on conditioned square footage:
Pricing in plain text: A REScheck alone is $72.50 for homes up to 5,000 sq ft, $129 for 5,001–6,000 sq ft, $179 for 6,001–8,000 sq ft, $229 for 8,001–10,000 sq ft, and $299 for 10,001–13,000 sq ft. REScheck + Manual J packages run $189–$415, and REScheck + Manual J + Manual S packages run $279–$499.
Turnaround: most reports are completed within hours of receiving complete plans (here's how ordering a REScheck online works). The biggest thing that slows a report down is missing information, usually window specs or wall insulation details. Send the full plan set up front and it goes fast.
Is REScheck Required for a Building Permit?
In most U.S. jurisdictions that have adopted an IECC-based residential code, you have to show energy code compliance at permit, and REScheck is the most common way to do it for new homes and additions. Some building departments call it an "energy report," "energy compliance certificate," or "REScheck certificate." It's all the same document. See how to obtain a REScheck compliance certificate for what gets submitted.
REScheck Frequently Asked Questions
What R-value do I need to pass REScheck?
It depends on your climate zone and adopted code. Under the unamended 2021 IECC, ceilings need R-30 (Zones 0–1), R-49 (Zones 2–3), or R-60 (Zones 4–8). Wood-frame walls range from R-13 in Zones 0–2 up to R-30, or R-20 plus R-5 continuous, in Zones 4–8. With the UA trade-off, one component can fall short if others make up for it.
What window U-factor does REScheck require?
Under the 2021 IECC, U-0.30 or better in Climate Zones 3–8 and U-0.40 in Zone 2. Zones 0–1 have no prescriptive U-factor requirement but a 0.50 maximum. Your adopted code may differ.
Can better windows make up for less insulation?
Yes, when you use the UA trade-off method. REScheck compares the total heat loss of the whole envelope, so better windows can offset walls or floors that fall a bit short. The more glass the house has, the bigger the effect.
Does a REScheck for an addition include the existing house?
No. Per DOE guidance, only the new portion of the building needs to be entered.
Does REScheck support the 2024 IECC?
Yes. REScheck-Web supports the 2024 IECC and Appendix RG. REScheck Desktop only goes through the 2015 IECC. Use the 2024 IECC only if your jurisdiction has adopted it.
Does passing REScheck mean my house passes inspection?
Not by itself. The report also includes an inspection checklist of mandatory items, like blower door testing, duct testing, and air sealing, which are verified in the field.
Who can prepare a REScheck?
Anyone with the plan information can run REScheck-Web. Most jurisdictions don't require a licensed professional. That said, errors in code selection, climate zone, or insulation inputs are the most common reasons reports get rejected, which is why many builders use a professional. More on that in who can complete a REScheck.
How much does a REScheck cost?
The software is free. Professionally prepared reports at Rescheck Review start at $72.50 for homes up to 5,000 sq ft, and most are completed within hours.
Is REScheck the same as a Manual J?
No. REScheck shows energy code compliance for the building envelope. Manual J calculates heating and cooling loads for HVAC sizing. Many permits require both.
Can REScheck be used for multifamily buildings?
Yes, for low-rise residential buildings of three stories or less above grade. Taller residential buildings use COMcheck.
About the Author
Brad Buzzell, M.Ed. is the founder and director of Rescheck Review, a division of Certified Energy Raters, LLC, a RESNET-accredited HERS Provider. He's a RESNET-certified HERS Rater with more than 25 years of experience in residential and commercial energy code compliance, and he prepares REScheck, COMcheck, Manual J, and Manual S reports for builders, architects, contractors, and homeowners nationwide. Reach him at (800) 671-1895 x702.
Sources
U.S. DOE Building Energy Codes Program: REScheck (supported codes, version 4.2.0 release notes, Desktop vs. Web)
DOE: How does REScheck show compliance for additions or alterations?
DOE: Energy Savings Analysis, 2024 IECC for Residential Buildings
International Code Council, 2021 International Energy Conservation Code, Tables R402.1.2 and R402.1.3, and Section R402.4
