SERVICES

R-Value (Thermal Resistance)

Resistance of a material layer or assembly to heat flow, in m²·K/W. Higher R = better insulator. Reciprocal of U-value.

Also calledr valuer-valuethermal resistanceinsulation r valueresistance to heat flow
Related on InfraLens
CODES
IS 11239IS 3346
Definition

R-value (thermal resistance) measures how well a material or assembly resists heat flow. Units: m²·K/W. Computed per layer as R = thickness / k. Total R for an assembly = R_si + Σ(R_layers) + R_se. Reciprocal of U-value: U = 1/R_total. Higher R-value = better insulation.

Typical values
Interior surface R_si0.13 m²K/W
Exterior surface R_se0.04 m²K/W
100 mm rockwool2.63 m²K/W
50 mm EPS1.43 m²K/W
230 mm brick wall0.28 m²K/W
150 mm RCC slab0.09 m²K/W
200 mm AAC block1.11 m²K/W
Where used
  • Insulation specification — required R for target U-value
  • ECBC compliance checks
  • Comparison of alternate insulation materials
  • HVAC sizing
Acceptance / threshold
Per IS 11239 / ECBC 2017: R-values from material k (per IS 3346) and layer thickness; total assembly R must hit climate-zone target.
Site example
To achieve ECBC roof U-value 0.33 W/m²K → R_total = 1/0.33 = 3.03 m²K/W. Subtracting surface resistances (0.13 + 0.04) and RCC slab (0.09), insulation must provide R = 2.77 m²K/W. With rockwool k=0.038: thickness = 2.77 × 0.038 = 105 mm. Specify 110 mm rockwool.
Frequently asked
What is R-value of insulation?
R-value is thermal resistance per unit area, in m²·K/W. Higher R = better insulation. Computed as thickness ÷ thermal conductivity (k). 100 mm rockwool with k = 0.038 has R = 2.63 m²K/W.
How is R-value different from U-value?
R is resistance (m²K/W), U is transmittance (W/m²K). U = 1/R_total. Higher R = lower U = better insulation. R adds linearly across layers; U does not.
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