One thing that may be a factor is MUBEC - <https://www.maine.gov/decd/meocd/bbcs/index.html>. It looks like Porter's population is below the mandatory adoption level. You might want to call the town office and ask for information about this and other zoning concerns. MUBEC is fairly annoying in a common way for codes - there may be some benefits to following the code but there's a lot of red tape and fees involved in doing so.
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