I've been reading about adding rigid insulation to the exterior of a house to increase R-value. The discussion seems to focus on ensuring the sheathing is warm enough to ensure it will dry. The problem I see is that most installations seem to consist of faced polyiso or XPS, both which effectively act as a vapour barrier. Seeing as my house already has an interior poly vapour barrier, I'm not too convinced this is the way to go.
Has anyone ever used unfaced, or glass fiber faced polyiso such as Iko Enerair? Seems to me it would allow the wall to dry more effectively in case of moisture penetration.