Ceiling/ exterior wall insulation question

IF you are going to insulate an exterior wall, make sure vapor is addressed – it is critical. Most frequently XPS, EPS sheet or spray foam is the best way. I am not a fan of traditional fluffy insulation and plastic sheet. Finally, make sure your building envelope won’t be too tight – a leaky house overcomes many unaddressed code issues. And it also circulates radiator or baseboard heat under windows etc. Here in Brooklyn very leaky houses compensate for range hoods and bathroom fan makeup air, supplamenting a normally inadequate amount of combustion for boilers/water heaters in unenclosed rooms, as well as preventing chimney backdraft. In these old leaky houses “two wrongs make a right” – so be aware when removing only one of those wrongs. Also, indoor air quality here can be quite poor and it is wise to open windows when available, but thats only part of the year. When you are sealing up your envelope a lot of realities must be addressed or it could be unhealthy for occupants. Much of the material written in insulating is for newer houses that are designed to proper code for ventilation and combustion – i’ve been in my fair share of old houses and some would have serious issues if the building envelope were tightened up. Just be aware of the ramifications down the line of what you are doing, then you can safely address your insulation. I’m surprised this isn’t discussed more on the forum.