The energy design of a Passive House requires adequate information on the building envelope characteristics. A typical problem in building design is over-dimensioning of heating systems due to poor reliability of thermal characteristics of envelope structures, anticipated air leakages, anticipated thermal bridging, and poor knowledge of window and door properties. Over-sized heating systems cost more, their control is more difficult, and thus they consume more energy.

Therefore the U-values should include the effects of at least major thermal bridges. To accomplish this requirement, the U-value calculation should be carried out using 2- or 3-dimensional numerical methods, as hand calculations are not sufficient for, e.g., frame structures of wood or perforated steel members.

The goal in structural design should be in simple solutions that can be repeated in various projects. Thermal properties of structures can then be assessed adequately by using ISO EN 6946 or ISO EN 10112 standards.

The Passive House Planning Package (PHPP) allows for comparison of different building systems and insulation levels with regard to heat losses. Some structures, such as perforated steel members require 3-dimensional tools for even for simple U-value calculations.