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Benefits of Thermal Mass


        * The term ‘Thermal Mass’ describes heavyweight materials ability to store thermal energy. Using materials with thermal mass in the floor or walls of a building enables those elements in the structure to:

u Absorb heat from the sun during the winter day, and release that heat back into the living spaces at night or during cooler periods, producing more comfortable even temperatures.

u Absorb heat from the building during hot summer days having been cooled down via natural ventilation during cooler evening i.e. Provide ‘natural air conditioning’ producing more comfortable, even temperatures.

* Extract " Energy Smart" – Development Control Plan by The Sustainable Energy Development Authority N.S.W. Government 1997. 


   In Plain English, Thermal Mass properties, is the ability of a material to absorb heat, and release heat, such as boiling water, hot coals in fire, metals like copper or iron. 

   If in a heated room, that has had a door left open, allowing all the warm air to escape, then the door is closed again. The thermal mass of the walls and floor will begin to release heat  back into the air and hence, reheating the living space.  Or like getting back into bed, after being up for a few moments, compared to getting into bed initially.

  In summer, shaded and enclosed areas in the building will absorb heat from the surrounding warm air, cooling the living space.

   This chart demonstrates how the thermal mass properties of Formblock walls stabilized room temperatures for the month of January. Inside temperatures were kept to a range of 17° to 27°C, while outside temperatures ranged between 10° to 35°. Note, these figures were achieved without the assistance of heating or cooling devices.

Chart of daily temperature readings

(click to enlarge)

It is important to remember that, the benefits of thermal mass are dependent upon, where the structure is located, how it is designed, and how it is operated.

The interior walls of this hallway act as a heat bank, absorbing winter sunlight from roof windows above. The same roof windows from outside, facing winter sun. 

( click to enlarge)

 The above picture of a hallway in a residential dwelling that has roof windows that allow winter sun to fall onto the interior walls of the hallway. When the sun has gone the walls will begin to release the heat that was absorbed into the living space, heating the building. 

 In summer the sun will change position in the sky resulting in no direct sunlight energy entering the windows, and by keeping the home reasonable closed, the unheated walls will absorb any increase in ambient temperatures directly from the air in the living space, thus cooling the building. In the evening, if outside temperature become cooler, the house can be opened to allow the internal walls to re-adjust.


Links to articles about thermal mass on other websites;





Environmental Building News- 'Thermal Mass and R-Values: Making sense of a confusing Issue.' www.buildinggreen.com




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