Passivhaus (Passive House) Minimum Performance and Typical Physical Characteristics

So, what are the efficiency performance characteristics needed to reach Passivhaus (Passive House)?

The minimum performance characteristics of a Passivhaus (Passive House) are:
  • Airtight building shell ≤ 0.6 ACH @ 50 pascal pressure, measured by blower-door test.
  • Annual heat requirement ≤ 15 kWh/m2/year  (4.75 kBtu/sf/yr)
  • Primary Energy ≤ 120 kWh/m2/year (38.1 kBtu/sf/yr)
In addition, the following are recommendations, depending upon the climate of building site:
  • Window u-values ≤ 0.8 W/m2/K  
  • Mechanical ventilation system with heat recovery of ≥ 75% efficiency using low electric consumption @  0.45 Wh/m3 
  • Thermal bridge-free construction of ≤ 0.01 W/mK
Typical physical characteristics of a Passivhaus (Passive House) in a heat-load climate within the northern hemisphere:
Less typical physical characteristics of a Passivhaus (Passive House) in a heat-load climate within the northern hemisphere:

As part of the design and certification process PHI utilizes a sophisticated PHPP (Passive House Planning Package)--a very intense MS Excel spreadsheet/program--which takes data, in great detail, of the physical characteristics and components of the building.  PHPP, to high accuracy, predicts the performance characteristics of the building through extensive calculation and its determinations have been empirically verified as being highly accurate.  I believe no other energy modeling tool is as thorough as PHPP.

The one performance characteristic that is not calculated, but actually measured, is the air-tightness of the building.  This number is absolute.  If you don't empirically meet the target, while your building may be very energy efficient, it can not be classified or certified as a Passivhaus.

With respect to the calculated performance characteristics, since the performance numbers are a result of an aggregate of individual physical performance characteristics, we had a fair amount of flexibility over the design of the building structure.

For example, if you choose, as we did, to deviate from some of the recommended or typical approaches that could hurt the overall performance values, you can make up the performance deficits in other areas.  To use just one example: in our own project, we decided that we wanted an especially "bright" naturally lit home.

One of the ways of accomplishing this was to increase the amount of window glazings on the north ("dark") side (a big no no with PH in the Northern Hemisphere).  To make up the performance "penalty" for that decision, we could increase the insulation of certain walls or ceilings, improve air-tightness performance beyond the PH requirement, and/or employ a higher efficiency HRV or ERV ventilation system

Since the Passive House standard doesn't specifically mandate any one building approach, Lisa and I were free to pick our "battles," so to speak, allowing us to choose aesthetic appeal over optimal energy efficiency in certain aspects of our home providing we made up for those "losses" in efficiency, elsewhere.

As we wanted a luxury home, first and foremost, one where the energy efficient designs would be "invisible" or hidden from plain view, we prioritized what we wanted and where.  The PHPP program easily allowed for alternative modeling, simply by plugging in different physical performance values.  This way, we were able to determine, before actual construction where we would land at the project's completion.

We will explore each of these above listed items in greater detail, in future articles.