Passive House Extensions - Is there such a thing?

In theory a house extension can be built to passive house standards but remembering that the building is attached to an existing dwelling structure that is likely to be very energy inefficient, one wonders if there is any benefit from having the additional construction costs and often quirky exterior design that passive house standards often demand.

The following is a selection of articles on passive house design that could be accommodated within normal house extensions if you really want to approach something near a passive house for your home extension project.

• What is a Passive House
  
  What is a Passive House? - A building standard that is truly energy efficient, comfortable, affordable and ecological at the same time. Passive House is not a brand name, but a construction concept that can be applied by anyone and that has stood the test of practice.
• The Passive House has got it all
  
  The Passive House has got it all - The Passive House Standard offers a new level of quality pairing a maximum level of comfort both during cold and warm months with reasonable construction costs – something that is repeatedly confirmed by Passive House residents.
• The Pasive House How it Works
  
  The Pasive House - How it Works - Efficiency improves comfort - The Passive House is the world leading standard in energy-efficient construction: A Passive House requires as little as 10 percent of the energy used by typical central European buildings – meaning an energy savings of up to 90 percent. Owners of Passive Houses are barely concerned with increasing energy prices.
• The Passive House Secret
  
  The Passive House Secret - The Passive House concept doesn’t only work on paper – Built Passive House examples around the world prove that it also works in real buildings. See also: Passive House Data Base.
• Passive House Definition
  
  Passive House Definition - A Passive House is a building, for which thermal comfort (ISO 7730) can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”
• Passive House Insulation
  
  Passive House Insulation - The principle - In low-energy buildings the entire building envelope is highly insulated. The building envelope consists of all the building elements which separate the inside from the outside. Its main purpose is to provide for a comfortable indoor climate – irrespective of the outdoor climate which is determined by the weather.
• The level of insulation in Passive Houses
  
  The level of insulation in Passive Houses - 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.
• Airtight Construction in a Passive House
  
  Airtight Construction in a Passive House - Indoor air has a higher water vapour content (absolute humidity) than outside air - if not dehumidified. In a cold climate, indoor air is cooled during exfiltration flow inside out. The colder air can not keep the high amount of water vapour - condensing will occur at a certain place within the construction. This may lead to serious damage. The process described here is the main reason why external building structure has to be built airtight.
• exhaust air systems with heat recovery
  
  exhaust air systems with heat recovery - Ventilation will only work properly if used air is continuously being removed from the kitchen, bathroom, toilet and other rooms with high pollution and humidity. In return, fresh, unused external air is supplied to the living room bedrooms and functional rooms.