Thermal mass

Oak Lawn Train DepotThermal mass refers to a material’s ability to absorb, store, and later release radiant heat.

Brick, slate, concrete, porcelain, stone all have high thermal mass. Walls and floors with a high level of thermal mass will improve building comfort and lower heating and cooling bills – and reduce greenhouse gas emissions.

These materials can be combined with passive solar design. Floors and walls of these materials are situated so that sun will shine on these surfaces through south-facing windows. During the day, these materials will be warmed by the sunlight. In the evening, they will slowly re-radiate their heat into the room.

In summer, they moderate temperature fluctuations in the room, again because they absorb heat more slowly.

It is possible to have too much solar gain from windows. Using materials with high thermal mass can help to optimize the solar design. At the latitude of southern Manitoba, the amount of south-facing glass should not exceed about 8% of the heated floor area. By adding thermal mass, this percentage can be increased. (1)

Thick wall materials with natural breathable plasters, rather than standard wood-framed walls, can achieve optimal thermal mass. These walls may be constructed from insulated concrete forms, logs, straw clay and straw bales.

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