Sealant was applied to both the jambs and the foam before the preassembled PVC casings were fastened in place.
To allow for water and air movement between the shingles and the foam, the shingles were installed over Home Slicker, a 1/4-inch-thick nylon mesh.
The retrofitted rigid foam serves as an air and water barrier. It's sealed with continuous beads of sealant to both the self-adhering flashing around the existing windows and the new PVC casings. At the sill, any water that manages to penetrate the casing is directed out over the foam and into the Home Slicker drainage matrix by a custom metal flashing.