Zoning is the determining condition to divide a townhome or rowhome into more than one unit. In DC, R4 zoning allows for two units by right. Anything more than that would require a zoning variance. This can be accomplished by appeal to the Board of Zoning Appeals for a variance. This is time consuming and may not be granted. If you are in an historic district, any exterior work would have to be approved by the local design review committee and the Historic Preservation Office and its Historic Preservation Review Board. None of this is impossible, but this is not an easy task. For condo conversions, once again zoning will dictate if it is possible. Conversion documents will cost you several thousand dollars. In what neighborhood are you contemplating this? Feel free to contact me for any advice. firstname.lastname@example.org; billpanici.com; (202)277-4675.