Thermal Mass

Thermal mass can be used with nocturnal convective cooling or ‘night cooling’ for cooling buildings passively. Diurnal swing, i.e., the difference between daytime and nighttime outdoor temperatures, must be high for thermal mass to be an effective passive cooling and heating strategy.

Thermal mass helps to store heat within the building structure and moderate fluctuations in the indoor temperature. This heat storing capacity of building material helps in achieving thermal comfort for occupants by providing time delay. Hence, choosing appropriate building materials can largely effect the level of comfort within buildings. To meet NZEB design parameters, selection of building materials hold utmost importance in modulating indoor temperatures and hence reducing conventional energy loads.

Mass and density of a building material affects this heat storing capacity in buildings. High density materials such as concrete, bricks and stone have high thermal mass, while materials such as wood or plastics have low thermal mass. The efficacy depends on the placements of these elements with respect to direct irradiation of the sun.

  • Denser thermal mass materials are more effective passive solar materials. Thus denser the material the better it stores and releases heat.
  • Use thermal mass in climates with large diurnal temperature range.
  • Integrate thermal mass with an efficient passive solar design, by considering the placement of added mass. Effectively locate and distribute thermal mass.
  • Select appropriate mass colour with low reflectivity. Dark, matt or textured surfaces absorb and re-radiate more energy than light, smooth, reflective surfaces.
  • Do not substitute thermal mass for insulation. It should be used in conjunction with insulation.
  • For heating and cooling requirements, the ground floor is the most ideal place for thermal efficiency in winter and summer.

Online Resources



  1. TERI – Guidelines for Solar passive design for new buildings.
  2. Geetha , N., & Velraj, R. (2012). Passive cooling methods for energy efficient buildings with and without thermal energy storage – A review. Energy Education Science and Technology Part A: Energy Science and Research, Vol 29- 913 – 946.
  3. Bansal NK, Hauser G, and Minke G. 1994.
  4. Passive Building Design : A handbook of Natural Climatic Control, Amsterdam: Elsevier Science B.V. Gupta C.L 1994.
  5. Energy Contents of building materials for India. Paper presented at the Green Architecture Festival.
  6. Sustainable building design manual Volume 2.


  1. Dynamic Thermal Properties Calculator by The Concrete Centre
  2. Climate Consultant
  3. OPAQUE by University of California, Los Angeles

Thermal mass regulates the temperature of the space by controlling the amount of thermal energy stored in the building. Heavy thermal mass buildings can keep the spaces comfortable for several hours even after the HVAC system is switched off.

Heavy thermal mass also delays the ingress of heat, and when combined with natural ventilation and night-purge strategies, can ensure that the building is pre-cooled naturally in the morning and stays cool even after the outside temperature soars.

In warm and humid climates, low thermal mass buildings eliminate heat build-up and dissipate heat quickly to the ambient.