U-values (thermal transmittance) of external walls, floor slabs and roof areas of Passive
Houses range from 0.10 to 0.15 W/(m²K) (for Central European climate; these values may be slightly higher or lower
depending on the climate). These values are not only benchmarks for all construction methods but also the most
cost-effective values at today's energy prices.
The heat losses during cold periods are thus negligibly small, and the temperature of the interior surfaces is
nearly the same as the air temperature, irrespective of the type of heating used. This leads to a very high level
of comfort and reliable prevention of building damage due to moisture build up.
In warmer climates or during summer months, good insulation also provides
protection against heat. Effective sunshades for the windows and sufficient ventilation are also
essential to ensure a maximum level of comfort during hot periods.
Good insulation and airtight construction have proved to be extremely effective in Passive Houses. Another
essential principle is ”thermal bridge free design”: the insulation is applied without any “weak
spots” around the whole building so as to eliminate cold corners as well as excessive heat losses. This
method is another essential principle assuring a high level of quality and comfort in Passive Houses while
preventing damages due to moisture build up.