The PassivHaus standard is extremely rigorous, and may be simply unattainable by houses that were built to conventional construction standards. The EnerPHit retrofit standard was created with older houses in mind, with a set of of requirements that still far exceed modern code. There are currently several hundred EnerPHit houses in the world, but none in the United States.
EnerPHit certification has the following requirements:
- less than 25 kWh/(m²a) (about 7.9 kBtu/sf/yr) for heating and cooling
- Air tightness better than 1 ACH @ 50 Pa
- Total energy useage ≤ 120 kWh/m2/year (38.1 kBtu/sf/yr)
What does that mean? An EnerPHit home will be 4-6 times more energy efficient than a conventionally built new home. Because the standard is for existing housing stock, it’s entirely possible that a remodeled home will perform at 10X its previous efficiency.
Why not just remodel to PassivHaus standards? Part of the problem is that older construction is full of interesting choices that simply cannot be made energy efficient without tremendous cost (we’re facing that right now with our chimney). The other part of the problem is siting. Houses are very rarely built with solar facing in mind, and if you live in the city, your house is often shaded at least part of the year by neighboring buildings and trees. Without that sunshine to act as your primary heating system, the amount of insulation required becomes prohibitive.
But really, the idea is to give an existing structure a new, more efficient life. In our case, it means that despite the fact that we’ll be almost doubling the usable square footage of our home, it will need about 30% of our current energy consumption. Or, put another way, our entire remodeled home will use about the same amount of energy to heat and cool as our living room currently does.