You might need a permit. Not everyone does and even sometimes those who do need a permit do not apply for one. Each municipality sets their guidelines for what types/size of buildings need a permit in their area – sometimes this is based on square footage or whether they consider it a “permanant structure” – but this is all decided by your local permit office. If you are applying for a permit, you should always go through this process BEFORE you order your greenhouse – depending on local wind/snow load requirements you may need additional reinforcements or supports to reach your local requirements. You may also find other restrictions for placement that may mean you have to limit the size or location. If you are going to get a permit, it is always best to know the restrictions ahead of time.