How do I know if I need a permit for my greenhouse?

Not every greenhouse will need one.

Securing a permit depends on many factors including the municipality’s building codes. As you can guess, these codes vary from county to county. Other factors include foundation, proximity to property lines or setbacks, glazing and size of the greenhouse. We find that structures less than 120 square feet (10x12 and smaller) do not usually require any permitting for a non-permanent structure. 

But what makes a greenhouse permanent or not?

A pressure-treated wood foundation is considered temporary and easily moved.