tRwaarde

tRwaarde is a term used in Dutch building physics to denote the total thermal resistance of a building element, taking into account both conductive heat transfer through materials and radiative heat transfer between surfaces. The prefix t can be read as an indicator of a “total” or “combined” resistance, distinguishing it from a purely conductive R-waarde.

In practice, tRwaarde combines the classical conduction resistance of layers in a wall, roof, or window with a radiative component that arises from heat exchange between internal and external surfaces. The radiative part depends on surface properties such as emissivity and the geometry of the element, and is typically estimated with simplified models that treat the radiative exchange as an additional resistance in series with conduction.

tRwaarde is used mainly in Dutch energy performance discussions and product specifications where radiative effects are relevant, for example in certain window and cavity-wall assessments. It is not a universally standardized quantity in international building codes, and in formal energy labeling the more common measures are U-values (overall heat transfer coefficients) and R-values for pure conduction.

Because definitions and calculation methods can vary, it is important to consult the specific regional or product-specific guidance when encountering tRwaarde. In many contexts, tRwaarde complements, rather than replaces, the standard R-waarde and U-value figures used for design, compliance, and certification.

See also: U-value, R-value, thermal conductivity, emissivity.