And how do you get fresh air in? Also the problem of heat transfer is never by gaps in the walls, at least not for buildings in western and central Europe. The problem is heat conduction through the window panes. And that is with isolated windows already. Also it is impossible to get a brick wall air tight. Leave alone you create a great environment for water to leak in and damage everything.

A building needs to be able to "breathe" in order to get rid of the humidity that is generated inside.