Exterior insulation with ICF
We’re trying to continue making progress on our pretty good ICF home in climate zone 5 and are at a crossroads on the exterior work. The walls above ground are 4″ of concrete, 2.5″ EPS foam on each side of the concrete – so about R-23.
For reference, we will have an insulated, un-vented roof with conditioned attic. Planning on R-23 over the roof deck and R-15 in the rafter cavities.
We have covered the roof deck with water & ice shield to help improve air tightness (belt and suspenders), which folds over the edges onto the ICF. The rafters end inside a fascia board, flush with the exterior walls. We will install applied or ‘false’ rafter tails/eaves and rakes in the near future.
In the interim, we have had some water intrusion, I think with water coming off the roof, down the ICF, and inside at the window bucks and cold joint between the top of the basement ICF and the above grade ICF. I’m hoping that getting the overhangs on the roof and the siding up with a rainscreen will take care of all that.
The garage is for all intents and purposes detached/adjacent and is 2×6 stick framed and sheathed with Zip. The concrete floor has PEX over rigid foam for radiant heat. We plan to keep the garage maybe 50F in the winter. I think we have plenty of room in the walls for insulation, but is there any major (cost-effective) advantage to adding exterior foam over the Zip on the garage?
Appreciate any suggestions, particularly with regard to if it would be really worthwhile to add a little more insulation on the exterior of the ICF on the house.