(i'm just starting on a greenhouse based on your old mother earth article and we're pretty excited about it)
I would be interested in your thoughts on adapting your underground house designs to cold climates. (colder than Idaho!) The frost can go pretty deep here (water pipes buried to eight feet). The dirt is warmer than the air, but it still could be a pretty massive heat sink.
I would have a lot less glazing but still try to optimize for some passive solar gain.
What type of insulation works best? Is there a cheaper or greener underground option than polystyrene?
How much mass would you incorporate inside the insulation envelope, and where would it be? ( I am leery of the passive annual heat storage concept as it seems like it would be really really easy to screw up the calculations and cook yourself all summer or never warm up in the winter, or have to wait years for it to equilibrate...
thank you so much! (just watching a big storm swirling overhead and wishing i had an underground house..)