It's the purview of the NCC, but not totally.  The house did not become unlivable the moment Harper moved out.  Trudeau assessed, and quite correctly IMO, that the building was not a livable building for his family and the NCC agreed.  
There is no reason for Trudeau not to comment on this since he already commented before the old building  was not suitable.  He must have an awareness of what he considers to be suitable.  His lack of comment suggests he's OK with it.