Due to its cell structure and composition, wood is a natural thermal insulation material with a thermal conductivity value lambda = 1,12 w / mK. Therefore, the thermal capacity of wood is especially important and makes it a poor conductor of heat. In addition, a wooden house contains no thermal bridges, which is the main reason of heat loss for a building. Wood is 190 times more thermal insulating than concrete, 564 times than iron and 1818 times than aluminum. As a consequence, a wooden house achieves approximately 50% savings in annual energy required for cooling and heating.
Terminology of a few key values in regards with thermal insulation of a building.
Coefficient of Thermal Conductivity (lambda value): It is the amount of heat (in Watt) which is transferred through a material of 1m thickness, when the temperature difference between the inner and outer surfaces is equal to one degree Kelvin 1⁰K. (The difference in temperature of one degree Kelvin equals the temperature difference of one degree Celsius)
The coefficient of Thermal Conductivity lambda of a material is measured in Watt per meter and degree Kelvin (W/mK) and is dependent on the nature of the material itself, its structure, temperature, humidity and pressure.
The lower the lambda value of a material, the better its thermal insulation properties.
Coefficient of Heat Transmission (U value): It is the amount of heat (in Watt) that is transferred through a square meter surface of a structural element, of a certain thickness d in a certain period of one hour, when the temperature difference between the inner and outer surfaces is one degree Kelvin 1⁰K. In other words, it measures how easily penetrates the heat through a material or materials’ layers (system).
The coefficient of Heat Transmission U value is measured in Watt per square meter and degree Kelvin (W/m²K) and mathematically is expressed by the formula U = λ / d where λ is the thermal conductivity coefficient and d is the thickness of the material.
The lower the U value of a structural component, material or system, the better its thermal insulation properties.
The coefficient of Heat transmission U value of a wall system is affected by the thickness in combination with the lambda value of the individual materials of the system.
Comparative table of values of different construction materials:
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