Bedroom Window Opens to Large Shaft, Still a Legal Bedroom?

[Will Johnston]

I'm looking at a long, skinny rowhouse that's currently configured as a 2 unit, but could probably be reconfigured for three units for either rental or condo conversion.

Several of the existing bedrooms have their only window into a shaft that I'm pretty sure was put there explicitly for the purpose of allowing light into the house.  It's fairly sizable, probably 2.5' wide x 15'+ long.

I'm trying to figure out if the windows into this shaft would count as a second means of egress, allowing the rooms attached to it to be legal bedrooms.  If the answer is no, there's not a great way to configure the thing, as I'm pretty sure it was built with this in mind.

One thought I had was that perhaps a fire escape ladder could be installed to allow access to the roof and then another ladder or stairs installed on the roof to allow access to the yard.

Any insight would be appreciated.  And this is in DC, so if anyone has any specific experience here, that would be great!

Thanks!
Will