As a permaculture design graduate and an intermediately experienced organic farmer, it has always been my understanding that a hoophouse or greenhouseshould be placed east to west to maximize sun exposure. We have just purchased a farm in south western maine, the property is south and slightly east facing. Until doing a little research i was going to place a a 96' x 20' hoophouse east to west in a spot that gets full sun from 8:30 am on but am reading that some people are running them north to south for better ventilation. Any thoughts would be greatly appreciated.
Our polytunnels have a N-S orientation because our prevailing winds and gales come from the West. We reckoned that if they hit the gable end full on the result would be disastrous. With a N-S orientation the strongest winds "slide" over the curved sides. Our first polytunnel was erected in 1997 and we have only had to replace the plastic once so far. We did also plant shelterbelts to the West (in 1996, running N-SSW) and North (in 2000) though.
So I guess the answer depends, as so often, on the individual site.