It's energy efficiency, but also old buildings. They weren't designed with insulation & sealing in mind, and as a result can actually depend on leaking lots of

It's energy efficiency, but also old buildings. They weren't designed with insulation & sealing in mind, and as a result can actually depend on leaking lots of heat to control condensation, mold & mildew. Seal them up and suddenly... Newer buildings are designed with tightly sealed rooms & thick insulation in mind, and thus don't generally have big condensation problems.