I didn't know the difference but the firewall as we call it is a mason block wall with and 2-3 inch air gap and then another mason block wall between our homes, sadly for me the only thing that is not covered with this wall is the soffit as it overhangs the outside wall about 2 feet.
from what Google says in a duplex there is no firewall it's just a normal wall with fire retardent drywall, glad I don't have a duplex and this explains why I can barely hear my neighbours, they have 4 kids and 6 dogs, so very happy there is a huge ass wall between us lol.
I am taking pictures and getting the roof shovelled off this week, once spring is here, up go the heating cable as I can't count on the new owner doing anything about the attic, hopefully they will insulate the attic but I ain't counting on it, so heating cables it is. Can't count on Simcoe County to have a stand-up agent as everything they do to that house has been half-assed, I can hope
the big difference I can see is the house next to me could burn and if the soffits don't spread it then we would be fine ( our course it would affect us but I would have a house still ) these places were built by the county in 1959 so I guess that was the code for semis back then, where they are moving it's a true duplex, just drywall and frame between them and the neighbour so if sneeze you can hear it, no thanks