R

Data sources & methodology

Every number on InsulationRValues.com is compiled from a primary document and links to it. Where credible sources disagree, the page shows the range and names both. R-values are label values at a 75°F mean temperature unless stated (FTC 16 CFR 460.5)[1].

How the data is sourced

  • Source hierarchy. Building codes and government documents first, then standards and national-lab reports, then manufacturer data sheets.
  • Every figure linked. Each number links to the primary document it comes from; the per-figure citation list is shown on each page.
  • Ranges. Where credible sources disagree, the page shows the range and both sources rather than picking one silently.
  • Costs. Cost figures are estimates, not sourced prices. The cost model is being rebuilt on RSMeans-based data published by PNNL/DOE and the NREL residential measures database; cost figures are labelled as estimates until then.
  • Corrections. Material changes are logged on the corrections page. See the editorial policy for the full process.

How assembly R-values are computed

Clear-wall R-values are never hand-typed; they come from one parallel-path method using ASHRAE 90.1 framing fractions[2] (25% of the wall is framing at 16 in. o.c., 22% at 24 in. o.c.). The reference wall is the interior air film, ½" gypsum, the cavity or stud, 7/16" OSB, vinyl siding, and the exterior air film; continuous insulation is added to both paths. Results are labelled “clear-wall (studs included)”; whole-wall performance is lower.

2x6 cavity R-21, 16 in. o.c. (framing 25%):
  common layers (interior+exterior films, 1/2" gypsum, 7/16" OSB, vinyl siding) = 2.53
  stud path:   2.53 + stud 6.76 = 9.29  (U 0.1076)
  cavity path: 2.53 + 21 = 23.53  (U 0.0425)
  U = 0.25 x U_stud + 0.75 x U_cavity = 0.0588
  clear-wall R = 1/U = 17 (studs included)

Code editions

Code minimums always name the edition. The site uses the 2021 IECC Table R402.1.3 values[3]; the 2024 IECC is the latest edition and adoption varies by state.

Cost figures

Cost figures are being rebuilt on NREL's Residential Efficiency Measures Database (REMDB 2024, in 2023 dollars)[4]; until then the site's cost figures are under review and are labelled as estimates.

Update cadence

Pages change when their sources or a correction require it; each page shows its own Updated date. Material changes are logged on the corrections page.

Sources used, by publisher

49 verified data sources across 45 publishers, retrieved Oct 2026.

Advanced Energy (Davis & Dastur); co-funded by U.S. DOE NETL (DE-FC26-00NT40995)

ASTM International

Atlas Molded Products (division of Atlas Roofing Corp.)

Bonded Logic, Inc. (Chandler, AZ)

City of Saskatoon Building Standards (reproducing NRC National Building Code of Canada 2015)

City of Seattle SDCI (adopts WA State Energy Code App. A)

City of Seattle SDCI (reproduction of ICC 2021 IBC)

City of Seattle SDCI (reproduction of ICC 2021 IRC)

Federal Trade Commission (eCFR)

Greenfiber

Home Innovation Research Labs (NAHB subsidiary), prepared for NAHB

ICC Evaluation Service (holder: SOPREMA Corporation)

ICC Evaluation Service (ICC-ES)

Internal Revenue Service (IRS)

International Code Council (ICC)

International Code Council (ICC) - reproduced by Virginia DHCD

International Code Council (ICC) / State of Colorado model code

Johns Manville

NAHB (National Association of Home Builders)

National Renewable Energy Laboratory (NREL)

Natural Resources Canada (Government of Canada)

NOAA National Centers for Environmental Information

O*NET OnLine (U.S. DOL/ETA) citing Bureau of Labor Statistics 2025 wage data

Oak Ridge National Laboratory

Oak Ridge National Laboratory (Wilkes & Childs)

Owens Corning

Owens Corning (Thermafiber)

Owens Corning Foam Insulation, LLC

Pacific Northwest National Laboratory (PNNL) for US DOE Building America

Pacific Northwest National Laboratory / US DOE Building America Solution Center

PNNL for US DOE

R-Shield / Premier Building Systems (reproducing NRCA data)

RESNET / ICC (ANSI standard)

Rmax

ROCKWOOL

Sika Corporation

State of Florida (Florida Building Commission), published by ICC

U.S. Department of Energy (Energy Saver)

U.S. DOE Building America Solution Center (PNNL)

U.S. Energy Information Administration

US Census Bureau

US DOE (CMEI / SCEP)

US DOE Building America Solution Center (PNNL)

US EPA ENERGY STAR

US Federal Trade Commission (16 CFR 460)

Known gaps

Sources not yet verified, or facts no verified source covers yet. They are tracked so pages are not filled with unsourced numbers.

door-u-factors — gap: none yet
fenestration-u-factors — gap: none yet
garage-door-insulation-kits — gap: none yet
garage-door-thermal — gap: none yet
icf-products — gap: none yet
log-walls — gap: none yet
metal-building-insulation — gap: none yet
retail-material-prices — gap: none yet
canada-code-tables — candidate: RSI/mm for insulation types (secondary)
cost-context — candidate: context only
doe-energy-saver-status — candidate: page status only
foam-thermal-ignition-barriers — candidate: thermal barrier and ignition barrier materials
installed-cost-retrofit — candidate: order-of-magnitude per-project bands only
irc-attic-ventilation — candidate: 1/150, 1/300; unvented attic R-values by zone

Sources

  1. US Federal Trade Commission (16 CFR 460) — 16 CFR Part 460 Labeling and Advertising of Home Insulation (FTC R-value Rule), via Cornell LII e-CFR mirror - § 460.2 (retrieved Oct 2026)
  2. ASHRAE / ANSI / IES — ANSI/ASHRAE/IES Addendum ay to Standard 90.1-2022 (approved 2024-10-31), Normative Appendix A sec. A3.4.1 (retrieved Oct 2026)
  3. International Code Council (ICC) — 2021 IECC Errata (complete) - Table R402.1.3 entry, Printings: All, posted 2021-08-10 updated 2026-09-18 (retrieved Oct 2026)
  4. National Renewable Energy Laboratory (NREL) — National Residential Efficiency Measures Database (REMDB) 2024 — machine-readable file REMDB_2024.12.23.xlsx (CC BY 4.0) (retrieved Oct 2026)

InsulationRValues.com is owned and operated by Moving Data Systems d.o.o., Smolnik 62, 2342 Ruse, Slovenia. Editor: Marko Visic. Last updated: 2026-10-22.