My house is about 10 years old...we moved in about 2 years ago.
The basement foundation walls have existing 1.5" (R-7) pink extruded polystyrene boards (2 x 8) fastened to them from the ceiling to just about a foot off the cement floor slab.
I have tuck-taped most of the joints so far between the sheets of foam.
My question is: If/when I finish the basement, should I fill in the space between the floor and where the existing foam ends? I figured the builder or previous owner didn't insulate this part because it is below the frost line.
Also, since the R-value is seemingly quite low, would it make sense to add additional insulation once the framing is complete (most likely 2 x 4 framing)?