Thermal bridges in passive houses and nearly zero-energy buildings

An important strategy for climate mitigation is reduction of energy use in buildings. One approach is to build or renovate buildings applying passive house design or a zero-energy building approach. The first step towards passive house design is reduction of heat losses, and therefore improving the thermal resistance of the building envelope. This is reached by adding more insulation and/or insulation with low thermal conductivity. A recent study shows that professionals unfortunately are not always aware of the concept of thermal bridges combined with different definitions of measuring of building elements. Furthermore, the effect of thermal bridges is usually taken into account using simplified methods which may not be correct. This paper explains the differences in different measuring methods which may be applied today according to European standards, and the possible impact on the specific values of linear thermal bridges. The results show that the relative effect of thermal bridges may increase when the thermal resistance of the building envelope is improved. It also shows that the difference between simplified calculations and more accurate calculations increases when the thermal resistance of the building envelope is improved. The case study shows that the effect of misunderstandings or carelessly handling of thermal bridges in the design phase may lead to an underestimation of peak power for space heating and energy demand for heating by 29 % and 37% respectively. To minimize the risk for undersized heating systems and increased space heating demand, subscripts indicating the applied measuring method (used in calculations to determine specific values of thermal bridges) should always be used when thermal bridges are presented.