What do the rules in Madison say about basement bedrooms? I know in my area, you must have an egress window in a basement bedroom. I personally wouldn't host in a basement without one: if there was a fire, it could be a very bad situation, and ethically, I woudn't do it. I do host in my home's lower level, and both bedrooms have large egress windows or a full door to outside. We have actually decided not to open another room in the flat as a bedroom because it doesn't have an egress window.
Airbnb doesn't have any specific rules around things like windows, but your listing shoud comply with the law in your area. Here's a link that may help:
https://www.airbnb.ca/help/article/376/what-legal-and-regulatory-issues-should-i-consider-before-hos...