Any of the PT foundations I have seen had exterior polystyrene insulation below grade.
Ray
Must be a local requirement.
I have not seem any insulation on the exterior of PTW foundations in the Edmonton area.
Are you sure it was polystyrene? other wise known as bead board.
If this is bead board then it is useless as it will absorb water and the insulation value goes to R1.
For exterior use foam board is the type to use as it does not absorb water.
Vern,
Yes white polystyrene. Have seen the blue high density foam board to.