Thermal Envelope & Energy Code Calculator

U-factor is the reciprocal of total thermal resistance: U = 1 / R_total. For an assembly with R-total = 19, U = 1 / 19 = 0.0526 Btu/h·ft²·°F.

Under IECC 2021 Table R402.1.2, the maximum allowable wood-frame wall assembly U-factor in Climate Zone 4 is 0.045 (requiring R-20+5ci or R-13+10ci).

An R-19 cavity wall yields an assembly U-factor of 0.0526, which exceeds the strict 0.045 maximum limit in Zone 4 unless continuous rigid insulation is added.

Prescriptive wood-frame wall U-factor limits: Zone 1 = 0.500, Zone 2 = 0.084, Zone 3 = 0.060, Zone 4 = 0.045, Zone 5 = 0.045, Zone 6 = 0.045, Zone 7-8 = 0.036.

SBC 601 sets thermal transmittance (U-factor) limits for building envelopes across Saudi Arabia's three primary climate zones (Riyadh Zone 1 U≤0.055, Jeddah Zone 2 U≤0.065, Tabuk Zone 3 U≤0.048).

Continuous insulation is uncompressed exterior rigid foam board that spans structural studs, eliminating thermal bridging through wood or steel framing.

R-value measures thermal resistance (higher is better insulation); U-factor measures overall thermal transmittance rate (lower is better thermal performance).

Air films (interior/exterior surface air layers) and exterior sheathing contribute ~R-1.5 to total assembly resistance before calculating U = 1 / R_total.

R-value measures thermal resistance to heat flow (higher is better), whereas U-factor measures thermal transmittance (lower is better): U = 1 / R_total.

The International Energy Conservation Code divides the US into 8 Climate Zones (Zone 1 tropical to Zone 8 subarctic) determining mandatory insulation minimums.

Continuous insulation is installed across all structural members without thermal bridges (e.g. rigid foam over exterior studs), dramatically reducing heat loss.

Due to thermal bridging through wooden studs (R-1.25 per inch), a 2x4 wall with R-13 batt insulation has an effective total cavity assembly R-value of approx. R-11.

2021 IECC / IRC Section N1102 specifies a minimum ceiling insulation rating of R-60 (or R-49 if full depth extends over wall top plates).

Concrete, CMU, and log walls store solar heat energy, allowing lower nominal R-value requirements in moderate climates due to thermal lag.

SHGC measures solar radiation admitted through glass (0 to 1 scale). Warm climates (Zones 1-3) mandate low SHGC (≤ 0.25) to reduce cooling loads.

2021 IECC requires mandatory blower door air tightness testing, limiting residential air leakage to 3.0 ACH50 (air changes per hour at 50 Pa).

In Climate Zones 3 through 8, IRC requires R-10 to R-15 vertical or horizontal perimeter rigid foam insulation extending 2 to 4 feet deep.

REScheck is a US DOE software tool that permits trade-off energy compliance (e.g., higher efficiency windows compensating for lower wall R-values).