attached greenhouse floor a few feet below ground: good/bad idea?
After seeing how well below-ground greenhouses work in cold areas, I was wondering if it would make any sense to have the floor of a heated sunroom/attached greenhouse/whatever you'd call it be a few feet below ground to take advantage of ground heat, if the roof was still six or seven feet above ground level. Like, would all that extra space counteract any heat gains? Any ideas? (no, we're not trying to heat with sun alone through the winter; I was just wondering if it might make sense to go below ground. also there aren't foundation problems; this is planning for a new house)