Side by Side
"Side by Side" townhouses have a neighbor behind or in front and on either side unless at the end of a building. The front door and sliding glass doors are side by side. The sliding glass door walks out to a private patio in most cases. One exception is one bedrooms have only a front door. Side by sides have three levels with a 1/2 basement or two levels with a backroom at basement level.
"Walkthrough" townhouses have neighbors on either side unless at the end of the building. You can walk through the unit from the front door through the living room and kitchen to the back door or sliding glass door. They are generally larger and always have three levels.
Firewalls & Neighbors
There is a firewall on one side of every townhouse unless the townhouse is located at the end of the building. A firewall blocks noise and prevents fire spreading. Units not separated by a firewall still have thick walls, but you may hear loud noises from one neighbor in a walkthrough and two in a side by side.