Hopefully the last question for a while.
Following a comment from Mark Siddall, I'm now wondering if I should be attempting to model the soil pipes in my planned PassivHaus. My current plan is to use HepVO self sealing waste traps for the upstairs bathrooms, which I believe means that I do not need an externally vented soil stack. On this premise, there will be no regular air flow through the soil stack unless there is a negative pressure event which will suck air out of the house.
However, there will still be soil pipes containing air at an uncontrolled temperature in several locations. Should I be modelling this also, or is it safe to ignore? I'm somewhat scared by the impact of the chimney, and hope that I won't have similar losses here.
Even if I don't need to model the losses, should I be looking at insulating the soil pipes?
Thanks to everyone for their advice and help so far.