eristeosuus

Eristeosuus is a Finnish term used in architecture, construction engineering and energy efficiency assessments. It describes the share or portion of a construction element that consists of insulation material, or the relative contribution of the insulation layer to the element’s thermal performance. The concept is used to quantify how much insulation is included in a wall, roof, floor or other envelope component and is commonly expressed as a dimensionless fraction, such as an area or volume ratio (A_ins / A_total or V_ins / V_total).

In practice, eristeosuus influences the overall thermal resistance (R-value) and the envelope’s heat transfer (U-value). A higher eristeosuus generally indicates greater insulating material content and lower heat loss, assuming material properties are constant. In energy calculations and building design, eristeosuus may be used to compare alternative constructions, perform sensitivity analyses, or meet regulatory or certification requirements. The exact definition and method of calculation can vary by standard, contract, or code; some contexts define it by the physical extent of insulation, others by the portion of the thermal resistance attributable to insulation relative to other layers such as mass or air layers.

Examples include a wall assembly where mineral wool insulation fills 40% of the cross-sectional area, resulting in an eristeosuus of 0.4, or a roof section where insulation contributes a specific share to the total R-value. See also insulation, building physics, U-value, R-value.