I am trying to get my new build R2000 certified. One of the things the R2000 consultant would like to see is more insulation in the crawlspace wall.

The crawlspace is to be heated and is completely below grade. the crawlspace wall is 4' high, 6" thick, and the footing projection is 4.5". the exterior side has brushed on damproofing and 5" of eps (2"+3"). the consultant would like to see another r8 of insulation added. obviously i'm not going to excavate to add more exterior eps so what do you guys suggest? i don't mind labour-intensive solutions but would like to keep the material costs down. also, do not want to use foam panels and spray foams are not available. is my best bet a short stud wall filled with roxul? is it not cool to use pressure treated lumber for the sill plate as it is located within the conditioned (i.e., living) space? i appreciate any tips. (outside design temp is -32 celsius)