Wet wall / open wall cavities and plumbing chases
Wet walls and open wall cavities are another important area to air seal. These can be found in line with existing top plates and can sometimes run along the exterior top plates. Usually they can be found along the bathroom walls. During the walkthrough in the rooms below look for small bump-outs, especially in bathroom but they can be found in other parts of the home.
An open cavity along the exterior
An open wet wall along the bathroom runner
Plumbing stack pipes tend to run up into the attic through these cavities. Look for those to help find the wet walls.
Larger cavities must be sealed with an air impermeable barrier like rigid foam board and expanding foam.