How do I calculate the U-value of a wall?

U-value is the reciprocal of Total Thermal Resistance (RT). RT is the sum of internal and external surface resistances plus the resistance of each material layer (R = thickness/conductivity). See Appendix A for the detailed method.

Where can I find the thermal conductivity (k-value) of brick or insulation?

Table 2 provides k-values for common building materials like brick and concrete, while Table 3 lists k-values for various insulating materials like glass wool and polystyrene.

What is surface resistance?

It's the thermal resistance of the thin layer of air on the inner and outer surfaces of a building element. Values are given in Table 5 and depend on the surface orientation and exposure.

IS 6670

: 1989

Code of practice for thermal insulation of buildings

CurrentSpecializedCode of PracticeBIMArchitectural · Insulation Materials

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This code of practice provides guidelines for the thermal insulation of buildings to enhance indoor thermal comfort and reduce energy consumption. It details climatic data for India, properties of various insulating materials, and outlines the calculation methodology for thermal transmittance (U-value) for building elements like roofs and walls.

Provides a code of practice for the thermal insulation of buildings.

Quick Reference Values

Thermal conductivity of common brick (k-value)0.72 W/m·K

Thermal conductivity of dense concrete (k-value)1.44 W/m·K

Thermal conductivity of glass wool (k-value)0.034 - 0.040 W/m·K

Internal surface resistance for walls (horizontal heat flow)0.12 m²·K/W

External surface resistance for walls (sheltered)0.08 m²·K/W

Internal surface resistance for roofs (upward heat flow)0.10 m²·K/W

Key Formulas

U = 1 / R_T — Overall heat transfer coefficient

R_T = R_si + R_1 + R_2 + ... + R_n + R_so — Total thermal resistance

R = t / k — Thermal resistance of a material layer

Practical Notes

While this code provides foundational principles, its requirements and recommendations are now largely superseded and expanded upon by the Energy Conservation Building Code (ECBC) and the National Building Code of India (NBC) 2016.

The core of this code is the calculation of U-value (Overall Thermal Transmittance) for a composite building element (roof/wall). U-value is the inverse of the sum of all thermal resistances in the assembly.

Moisture control is crucial. Ensure a proper vapour barrier is designed, especially for cold storage or in humid/cold climates, to prevent condensation and degradation of insulation performance.