Re: Plaster and Lath - remove or not to remove?
Howdy, first what is the attic insulated to? and what type of insulation? How are the windows? Storms? Is the floor insulated? I'd bet, as with allot of old homes, the attic does not have enough in it. An the attic access door likely not properly insulated and air sealed. If not enough attic insulation consider cellulose as it retards air movement and has fire retardant- be aware if the wiring is old( knob and tube do not install insulation over it as it can result in a fire). So consider easy fixs- check the seals of the doors & trim & windows and caulk as needed/ or weatherstrip. Caulk around any ceiling light fixtures to stop air movement. Insulate the homes first floor to r-25 if acessable & attic to R-49 . If you have a stick of incense walk around the windows with it and see if the smoke shows air movement- poor mans air infiltration test. HVAC been checked? If forced air have it checked to see if it is working properly. Before you open up the plaster walls.
Any an all of my comments are just my opinion and not to be confused with facts.