Do I have to finish my basement walls with drywall?
All building codes in the USA and Canada specify that plastic insulation (EPS) must be covered by a thermal barrier equivalent to 15 minutes of fire protection in habitable spaces. If the basement is classified as habitable space, then gypsum board must be applied but does have to taped and filled. Check with your local building official.
How do I protect the ICFs below grade?
All ICF walls below grade, that have habitable space on one side (basement), must have a waterproofing / dampproofing membrane installed. For walls that do not have habitable space on one side (crawl space, frost walls, etc.) the EPS can be left exposed to the earth. The EPS will not deteriorate when exposed to the earth.