Getting to .5 ACH @ 50 is pretty hard to do UNLESS you sprayfoam 1" or so over everything. With meticulous air sealing and 12" or more of cellulose in a wall it's still some work to get it under 1 ACH. A friend of mine recently built a house that he's winning all kinds of awards for and he only got it to .9. He only insulated with cellulose though. The only foam was used for air sealing and below grade. It's a 1,200 Sq Ft house and it basically doesn't need heat. It has a 7 BTU/h ASHP but it never really comes on. The owner turned it off when she went on a week vacation this winter (between 0 and 10 degrees F) and the house was 59 degrees when she came home. When there's cooking, lights and human presence nothing is really needed. So you don't really need = < .6 ACH @ 50 to have a passive house. But you need it to have a "passivehaus".
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