I am having siding installed and planned to have Tyvek installed. The contractor installs styrofoam or Tyvek but not both because they say the house would be too tight. They say on a celetex sided house like mine they use the foam panels. Isn't Tyvek for moisture, where the foam is just for a smooth nailing surface with a bit of insulating. Can I use both? My house leaks so much air now I doubt it would be to tight.