Understanding U-values |
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The U-value measures how well a building component, e.g. a wall, roof or a window, keeps heat inside a building. For those living in a warm climate the U-value is also relevant as it is an indicator of how long the inside of the building can be kept cold.
Comfortable indoor climate with good U-values
In both cold and warm climates good U-values are important measures for understanding the amount of energy that is needed to keep a comfortable inside temperature. Learn more about why u-values matter.
What is the U-value?
The U-value is a measure of the heat flow through a building element as illustrated in the figures to the right. The higher the U-value the more heat flows through so a good U-value is a low one as you want to keep heat inside the building or outside depending on the climate you live in. See u-values in action.
The technical explanation of the U-value
Getting a little technical the U-value physically describes how much thermal energy in Watts [W] is transported through a building component with the size of 1 square meter [m²] at a temperature difference of 1 Kelvin [K] (=1ºC). Thus the unit for U-values is W/(m²K).
So what is a good U-value? For external walls, roofs, etc. a U-value of less than 0.2 W/(m²K) can be called good. This value can be reached by using thermal insulation with a thickness of about 20 cm or more. For windows the U-value should be less than 1.0 W/(m²K).
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