SIP vs 2x6 with spray foam (energy efficient home building)

Yes, and I think that it's a lot easier to control ventilation than it is to control heating and cooling. The simplest ventilation system is windows that can be easily opened and closed and seal well when they are closed.

Where I live we can get more advantage from the sun than lots of places. In areas with dark dreary winters, it may not be worth designing expensive thermal mass into a house, and putting big windows on the south. It may be better to just keep the window area small and tighten and insulate the house well. Also, our summer nights get down right chilly by morning, unlike more humid places. So it's easy to cool a house down by leaving some windows open during the night, then closing them during the day before it gets hot. Ventilating in the winter is more of a chore, but it's just as important. You need to get rid of humidity so it doesn't cause mold or reduce the R value of your insulation. And you need to get fresh air into the house and get rid of all the pollution from cooking, burning wood, out-gasing plastic, breathing, etc. Just opening and closing windows at the right time of the day can be all that's needed, as long as you're around to do it and want to bother with it, and are gaining heat from the sun. But if you have to go off to work every day and can't be home when using the windows is most effective, then you have to come up with an automatic way of doing it. But that's just a matter of running a fan, opening a few vents, and being able to control all of it. A hvac system for a new house should be able to control ventilation as well as heating and cooling equipment.

I like the automatic ventilation because it can be constantly bringing in fresh air all day. And with a HRV you recapture much of the heat that would otherwise be lost. That was a great invention...and quite simple, really.

Mikes554, I was thinking of using this siding. Do you think this would work? I am just pipe dreaming, but this looks like a natural fit. I could save some $ by doing this myself.

Also, how do the rafters work on a sips house?