U-value: A guide to the energy efficiency and thermal insulation of structures

When it comes to building energy efficiency and insulation, one term stands out: U-value. It’s a technical measure of how much heat can escape through a structure, such as a wall, window, or roof. The rule of thumb is simple: the lower the U-value, the better the insulation of the structure and the less energy it takes to heat your home.

In practice, a low U-value means better living comfort and lower costs. A well-insulated house does not feel drafty, the floors are warm and the indoor temperature remains constant. Building regulations set minimum requirements for the U-values of different building components, but an energy-conscious builder often strives for values that are better than the regulations. By investing in high-quality insulation and choosing, for example, low-energy windows, you ensure that your home is not only energy efficient, but also very comfortable to live in.

• The U-value (thermal transmittance coefficient) measures the thermal insulation capacity of a structure – the lower the value, the better the insulation.
• A low U-value saves on heating costs, improves living comfort and reduces environmental impact.
• The calculation is based on the thermal resistance (R-value) of the material layers of the structure, which depends on the material thickness and thermal conductivity (lambda value).
• Finnish building regulations set strict maximum limits for the U-values of building components (e.g. wall ≤ 0.17, roof ≤ 0.09 W/m²K).
• The U-value of modern windows and doors is typically less than 1.0 W/m²K.
• From an energy efficiency perspective, it is essential to examine the U-values of the entire building envelope as a whole.