At what point in the construction of my house should spray polyurethane insulation be applied?

Normally spray polyurethane insulation is installed at the same point in the construction cycle as other types of insulation. That is, it should be installed after the rough plumbing, electrical wiring, and heating and air conditioning ducts have been installed. If you decide to seal the entire exterior house shell with spray polyurethane, spray insulation may need to be applied in some areas before the ductwork is installed.