12 October, 2010

Really, Really Thick Walls

By Christina Winter, Allied Member ASID
To really get an understanding of how a passive house cuts energy by 90%  you have to start with the bones of the house.  If you can wrap your head around 20" walls and layers upon layers that avoid thermal bridging and have a low thermal heat loss coefficient that is also airtight then you can start to understand the basics of how the walls are constructed in a passive house.  To better explain:

  • A thermal bridge is created when materials that are poor insulators come in contact, allowing heat to flow through the path created.  Insulation is of little help in preventing heat loss or gain due to the thermal bridging.
  • R-value means the measure of resistance of an insulating or building material to heat flow, which is expressed as R-11 or R-20 and so on, the higher the number, the greater the resistance to heat flow.  Europe reaches a level of anywhere from 38-52.  This level of insulation reduces the heat lost during the winter and the heat gained during the summer to extremely low levels. Once this is established then it becomes easier to keep the home at a comfortable temperature with very little energy.  Surfaces in the home will also remain at a constant temperature and help the home to stay within levels that are safe for all occupant of the home.
  • Airtight  Construction helps not only in energy savings  but also helps in humidity control.  In the long run this will also help the building structure and help keep humidity levels safe for all.

Below are some photos that best illustrate these elements:
All photos from www.passivhaustagung.de

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