A cementitious rendering is applied on the interior of the mass wall and coated with a vapor semi-permeable fluid applied water control layer. The rendering fills in the big gaps allowing the fluid applied layer to be applied in a continuous fashion. High-density mineral wool is installed directly against the fluid applied water control layer. Caveat - this is limited to climate zones 4 or lower. The assembly is not airtight enough and vapor tight enough from the inside to work in colder climates - unless the interior relative humidity is kept low during the coldest two months - less than 30 percent in climate zone 5 and less than 20 percent in climate zone 6 and in colder places forgeddaboudit.