My walls are 8 inches thick which makes the rooms small. Assessor is only interested in exterior size of house.
An assessment should not be confused with a RE listing. My house is not liveable presently. Plumbing and electricity has been removed and still needs to be replaced. The assessor said that they don't care about that. They just need to know how many rooms are in a 30x40 foot house. A RE agent would need to know the size of rooms, not an assessor. You may have those measurements on hand but don't depend on them helping you lower the assessment.
Another thing when doing the comparables, look at siding and roof materials. Brick is valued differently from wood siding.
Oh, and try to find comparables for your property that are different from the ones they used. If your house is unique, find another house that's unique in its own category.
Thanks for the reply on the thick walls.