Conditioned Attic – Roof Construction in ICF Home
We are building an ICF home in northern Indiana, climate zone 5A. It will be about a 3k sq ft ranch with a 1k sq ft unfinished basement. Exterior walls will be made from Build Block, using 4″ concrete forms above grade with thicker forms below. The builder tells me that they are effectively R-50 walls.
It looks like building standards say our overhead insulation should be at least R-38, but we’ve been talking about R-50. The bulk of the house will have a single sloping shed roof, with about 1/3 of the roof on engineered rafters over a cathedral ceiling and the remainder over trusses. We plan to have a sealed, conditioned attic. The HVAC contractor is working on calculating air exchanges for the attic space, to be completed by the combination ERV and whole house dehumidifier. Any suggestions on this (attic air exchanges) are welcome.
To make things more interesting, the interior climate will be controlled using hydronic/radiant ceiling panels from Messana.
My big question is with regard to roof construction. I had envisioned some sort of insulation within the joist cavity, OSB sheathing above, rigid insulation with staggered seams, Carlisle WIP 300 HT over that and sticking down onto the exterior ICF, covered by diagonally placed furring strips and a standing seam metal roof. The roof itself will be vented with something similar to Cor-a-vent behind the fascia, between the furring strips, and above the ice and water shield, which I am hoping should also serve as an air and vapor barrier.
Any suggestions on this construction method? How much rigid insulation do we need over the roof decking? I’m thinking long lag screws to fasten the furring strips….