How to check if addition work is permitted

[Alazar Wubet]

I recently purchased a townhome in NW washington DC and i am starting to suspect the addition at the rear of the house has not been permitted. I have checked on SCOUT if there were any permits pulled but there aren't any. The house is almost 80 years old and the addition could have been built back then but it smells like illegal construction. How do i check if it has been built illegally and if so what should i do to avoid paying hefty fines?