Old houses tend to pull moisture into and out of the insulation between summer and winter, which can become a problem above and beyond the high heat bills that

Old houses tend to pull moisture into and out of the insulation between summer and winter, which can become a problem above and beyond the high heat bills that they create. Matt Risinger had a great video where they were rebuilding a 1930s house and you could see where all the moisture had built up and wept back out of the insulation, staining the wood behind the plaster. My understanding is the problem with making old buildings airtight is the lack of proper vapor barriers under the house, especially if it was built on a slab. For homes built on crawlspaces, you can "encapsulate" them, which reduces energy losses and improves air quality. Typically encapsulated crawlspaces are ventilated and/or dehumidified, which is supposed to stop moisture ingress into the living space.