Rwaarde

R-waarde is a building science term used to quantify the thermal resistance of a material or construction element. It measures how effectively an element resists heat flow between indoors and outdoors. In general, a higher R-waarde indicates better insulation and lower heat loss.

For a single material, R equals thickness divided by thermal conductivity: R = d / k, with units in metric m2 K/W. For a multi-layer construction, the total resistance is the sum of the individual resistances: R_total = Σ(d_i / k_i) plus appropriate surface resistances. The thermal transmittance U is the reciprocal of R_total: U = 1 / R_total, and is commonly used in energy calculations and regulation.

R-waarde is used in Dutch and other European building regulations, energy labeling, and product specifications. It applies to walls, roofs, floors, and other enclosures. Windows and glazed elements are often described by their U-waarde, with lower numbers indicating better performance. Climate, installation quality, and moisture can influence effective R-values.

Conceptually, R-waarde corresponds to the international thermal resistance concept; in English-language sources R-value is typically expressed in m2 K/W in metric contexts or in ft2·°F·h/BTU in imperial contexts. The reciprocal relationship with U-waarde is common in energy performance discussions.