In my readings of ways to improve energy efficiency on a house I came across a few mentions of using polyisocyanurate foam core panels (e.g. Celotex) on the exterior of house under the siding... the argument being that having a thermal barrier like this reduces thermal bridging through the studs. I'm considering using this material on my old house which will be fully re-sided this summer. The proposed idea is to sheath the house as normal with OSB, then cover that with Tyvek, then fasten celotex panels to the studs, then finally apply pine clapboards to the studs (if we can find them!). Does anyone have any experience with this? Any info, opinions, advice would be greatly appreciated. Thanks, Genevieve