[krapht]

Sure, renovated old stock isn't airtight, but nobody needs that. I've been in some passive houses - net zero by virtue of the fact that they ventilate the bare minimum of air. Soon as you get some nasty furniture outgassing tons of VOC, ugh! Living quality goes waaaay down. Headache central. Same thing if you put a lot of people in one room - the bare minimum ventilation will cause CO2 concentrations to go up and again, headaches, dizziness, etc.

I don't believe in local stick build kits for your business. Every customer is going to consider the total cost of labor for your houses. I don't know if it's possible, but I hope you consider partnering with a modular home builder with an existing sales network. Clayton Homes or whatever. Then you only need to build to one standard (Fed DOT... I could be wrong though, never looked into the regulations too deeply) and you can leverage their sales and financing force.