Long-term experience with Passive House buildings is illustrated with two early large-scale projects, a school and an office building located in Germany. Those were monitored in lump energy performance (school, commissioned 2004) and great detail (office, commissioned 2002), respectively. Moreover, they give an indication of the characteristics of such buildings subject to changes in usage intensity. Both buildings generally performed as expected with the school facing occasional overheating in the summer due to inflexible shading controls. Following an extension in schooling hours, the addition of a canteen was required and the ventilation system was adapted to the changed usage. Nevertheless, the building’s user comfort and energy performance remain high, despite exceeding the Passive House primary energy target slightly due to increased electricity consumption. The office likewise meets the calculated efficiency in operation. The ground-coupled cooling worked well despite greatly increased internal heat gains due to unexpected usage. This extra heat input did not, however, exhaust the geothermal (passive) cooling capacity for the future. Thermal comfort proved near optimal at all times, despite a very simple control regime of the one-circuit concrete core activation system for heating and cooling. In the last section, airtightness design and measurement experience in the UK and, particularly, the question of long-term stability of the airtight building envelope are assessed. It was found that measurement results are not only repeatable in relatively short intervals such as a few months. The data available suggests stability of the airtight envelope over many years. Attention is required as regards the leakage of party walls of terraced buildings which need to be integrated in the overall airtightness concept. A high permeability of party walls in terraced buildings with a common airtight envelope presents a challenge for measuring airtightness. Long-term series of airtightness measurements exist for the Kranichstein House in Darmstadt, Germany, and prove the stability of the chosen airtightness concept. Moreover, results for 17 early Passive House buildings in Germany in eight locations and various construction types revisited in 2001 (1.4 to 10 years after the initial airtightness test) suggest stability of airtightness values over time. Great advances have since been made in materials and methods available and the general understanding in the industry. This is supported by a large sample of 2934 Passive House projects of varied construction materials, locations, sizes, and usages that yielded an average airtightness test result as low as n = 0.41 h.