Our Passive House (Passivhaus) Design Targets

Before we began actual construction of the home, we worked on the architectural design, taking as best we could at the time, the requirements we would need in order to achieve or exceed the Passive House (Passivhaus) standards.  We worked with a PH consultant who plugged in a host of information from our basic floor plan and elevation take-offs.  Without having every conceivable design element taken into account, we started with a "broad-stroke" approach, and this is what we determined were our baseline targets assuming the following physical dimensions of the home:
  • The TFA (treated floor area) was to be approximately 6600-6700sf.  This space is considered the total amount of conditioned floor-space.
  • The cubic volume of the home would be approximately 60,000cf.
  • Walkout basement, partially below grade
  • Front of home, facing due south.
  • Use of more than recommended maximum amount of rear (north) facing windows and a fair amount of window glazing on both the east and west-side of the home.
What the PHPP program indicated that we started with this baseline:

Windows = U-value 0.19, SHGC=0.45
  •     North facing = 236SF
  •     South facing = 329SF
  •     East  facing  = 90.5SF
  •     West facing  = 110SF
Exterior Walls Above Grade = R47
Exterior Walls Below Grade = R44.6
Concrete Slab =  R42.7
Treated Floor Area = 5743
ERV CFM Average = 207 CFM Continously (.26 ACH in volume) @ 83% recovery efficiency
ACH 50 (Air changes per hour at 50 pascals as verified by blower door test)  = 0.6 ACH50

Roughly calculated:

Specific Space Heat Demand (SSHD) in imperial units of 5.65 Kbtu/sq ft/year (maximum acceptable PH value is 4.75 Kbtu/sq ft/year)

While we were close to attaining these extremely rigorous energy performance standards, using these rough figures, we knew we needed to improve where ever we could, to be certain that we would achieve or exceed PH.

However, even if we hadn't attempted to improve our design and hit the PH targets, Lisa and I still would have and extremely energy efficient home!  But, of course, not only did I want to hit Passivhaus (Passive House) targets, I wanted to exceed them.  That's just my nature...always trying to push the outside of the envelope.

I can not stress enough, how important it is to pre-certify, if you will, what your design targets are.  This will help point the direction for material selection and building approach as early as possible as well as identify potential weak spots.

Without a doubt, the earlier in the project design elements are properly identified and techniques defined, the less expensive the overall project development costs will be.

Looking at these rough numbers, I knew we had some work to do, particularly on the window front.  But, at the very least, we had a sufficient starting point, baseline.

Our next step was to determine which building methods and materials were we going to use...