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Thermal EngineeringP0

Thermal Resistance Calculator - R-Value

Calculate thermal resistance (R-value and U-value) for composite walls with multiple layers.

Inputs
Enter your values below

Brick 100mm

Brick ≈ 0.8 W/mK

Insulation 50mm

Mineral wool ≈ 0.04 W/mK

Plasterboard 10mm

Plasterboard ≈ 0.16 W/mK

8 W/m²K for indoor still air

25 W/m²K for outdoor

Result
Overall U-Value
—
Enter values and click Calculate
Formula
1 ÷ (1 ÷ h_in + l1 ÷ k1 + l2 ÷ k2 + l3 ÷ k3 + 1 ÷ h_out)
Result unit: W/(m²·K)

U = 1/R_total. R_total = R_inside + Σ(L_i/k_i) + R_outside. Three material layers provided: L in m, k in W/mK. h in W/m²K.

Introduction

Calculate the overall heat transfer coefficient (U-value) for a composite wall assembly with up to 3 material layers plus convection resistances on both sides. U-value is the reciprocal of total R-value.

Calculation Example

100mm brick + 50mm insulation + 10mm plasterboard: U ≈ 0.62 W/m²K (well-insulated wall).

Inputs: l1=100, k1=0.8, l2=50, k2=0.04, l3=10, k3=0.16, h_in=8, h_out=25
Result: 0.624 W/(m²·K)

Engineering Applications

  • •Building insulation design
  • •HVAC load calculation
  • •Energy code compliance
  • •Wall/roof assembly rating

Frequently Asked Questions

What are typical building U-values?

Modern insulated walls: 0.2-0.4 W/m²K; roofs: 0.15-0.25; windows: 1.5-3.0; uninsulated solid brick: 2.0-3.0.

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Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.