@maureenk
It is strange looking at houses in the USA which are predominately built of wood and comparing them to the houses here in Luxembourg of the same sort of age, which are predominately built of stone. The house I'm sitting in right now is about 100 years old and has walls around 75 cm thick (= 30 inches) of local ironstone which, as its name suggests, is in fact iron ore and it's incredibly dense due to its high iron content.