Roxul Comfortboard rainscreen
Our home is located in Lincoln, NE (Zone 5). Existing wall construction is typical 1/2″ drywall, 2×4’s @ 16 oc with fiberglass batt insulation, 1/2″ sheathing (mostly fiberboard, some areas are OSB), house wrap & vinyl siding. We will be replacing our siding due to hail damage, so I thought it would be a good time to add exterior insulation to the walls.
For the exterior insulation, I am considering either EPS, Poly, or Roxul Comfortboard 80. I like the environmental impact and drying capability of Roxul; however, in terms of cost, EPS ($0.08/r-value) or poly ($0.12/r-value, using R-4.5 cold-weather derating) are both cheaper than Roxul ($0.18/r-value).
My understanding is that with EPS or poly, I can attach vinyl siding directly to the face of the foam insulation. All installation guides I have seen for the Roxul product have used furring strips. Are furring strips required with Comfortboard if I am installing vinyl siding, or could I attach the siding directly to my underlying sheathing similar to EPS or poly? If furring strips are required, I don’t think I can justify the additional time and expense over the EPS or poly.