Legal Question in Real Estate Law in Washington

I don't know without researching the question, but I would begin by calling a real estate agent. I would then call the building department. (Dial *67 first to ensure caller ID is blocked, especially when you call the building department.) In neither case should you give your name nor should you give any more specifics than that you remodeled extensively without a permit.

They will probably get you pointed in the right direction. Regardless of the answers, if some legal requirement is necessary, accept the fact you'll have to hit it head on, and in that case see a lawyer.

Next time, the best course is always to follow the law, like it or not. And as a practical matter in your case, I would expect that, unless you can have the work approved by the inspector, or you can hide it from your buyer, the decrease in value will be greater than the building permit would have been. If you are able to hide it from your buyer and there are problems later, you could be liable for misrepresentation. In that case the cost of legal defense would be well beyond the cost of the building permit.