Dämmwert

Dämmwert is a German term that denotes the insulating value or thermal insulation performance of a building element, such as a wall, roof, or window. It is used to express how well an element resists heat transfer between indoors and outdoors and is closely related to the concept of thermal transmittance.

In practice, Dämmwert is often represented by the U-value (W/m²K), which measures the amount of heat that passes through a square meter of the element per degree of temperature difference. Equivalently, it is related to the thermal resistance, R (m²K/W), where a higher R or a lower U indicates better insulation. For multi-layer constructions, the overall U-value is calculated from the sum of the layer resistances, plus interior and exterior surface resistances: U = 1 / (Rsi + ΣRi + Rse). Each layer’s resistance Ri depends on thickness d and the material’s thermal conductivity λ (Ri = d/λ).

Dämmwert is used in energy performance assessments, building codes, and construction planning to compare materials and verify compliance with regulations. Lower Dämmwert means less heat loss and higher energy efficiency. Values vary by element and construction: walls, roofs, and floors with modern insulation typically achieve lower U-values than older builds; windows and doors generally have higher U-values unless they use advanced glazing.

While Dämmwert describes thermal performance, it is not a single physical constant. It is an index that encompasses material properties, thickness, installation quality, and boundary resistances. The U-value remains the standard unit in many codes, with Dämmwert serving as a general term in German language contexts.