Nominal Hoop
spacing is 4 feet O.C. on typical greenhouse/hoop-house construction , however
you can space them closer if you like. On some applications such as summer
shade or bird net structure applications 6 ft is acceptable provided the
covering is removed before the winter season.
Typically greenhouse lengths are based on being divisible by 4 (feet spacing) For instance if you planned to build a 42 long greenhouse, consider going to 44 or even 48 feet. The longest greenhouse are normally 96 feet long this is because the poly typically comes in 100 ft. rolls and your poly must be longer than the house.