White Faced Thermax
Basements should be included in the building envelope.
Traditionally, builders have used the low cost solution of stuffing fiberglass into the framed floor over the basement to meet code. With the new building tightness standard this method is now a measure of the past which is great, because it didn't work anyway.
The most energy efficient way to approach a basement or crawlspace is to insulate the masonry foundation walls with a rigid foam product that is rated to be left exposed.
White faced Thermax fits this need perfectly.
By insulating the foundation walls we are effectively lining up our thermal barrier (the insulation) with the pressure boundary (the concrete foundation wall). This is a building science based best practice that reduces moisture (condensation) and dramatically increases comfort, especially on the first floor.
This measure is best paired with an insulated, pre-hung basement entry door at the bulkhead entry.