Vinyl siding is installed with backer board (insulation board), and the combination of these two layers creates a vapor barrier on the outside of the wall. However, replacement vinyl siding will make the problem worse. Many homeowners decide to solve the problem by having vinyl siding installed. Once these conditions begin inside a wall, the exterior paint often begins to peel from excess moisture. The moisture can enter the exterior sheathing and wood siding, often causing permanent exterior paint failure. This mass creates an inviting place for termites, carpenter ants, mold and dry rot.
When loose, blown-in insulation gets wet, it becomes a moist mass at the bottom of the wall cavity. That warm, moist vapor enters the wall through hairline wall cracks, outlets, switches and window trim. Warm, moist air is generated in your home by cooking, taking showers, running the dishwasher, having plants-even breathing. Instead, plaster walls are designed to allow the free exchange of air and moisture.
Old houses with plaster walls have no vapor barrier under the plaster to stop moist air from saturating the insulation. Loose-fill cellulose or fiberglass insulation that has been blown into the walls is one of the main causes of exterior paint failure, termites, mold and structural damage in old houses. If your historic house has original plaster walls, you should not blow insulation into the exterior walls. Wall insulation might seem like the obvious solution to heat loss in your historic house, but this is usually not a good practice.