Best rigid insulation to add to exterior of existing 2x6 wall with poly vapor barrier?
As part of replacement of T1-11 siding with fiber cement on a building in Zone 6A, I plan to add 2 inches of exterior rigid insulation outboard of existing 5/8 inch plywood sheathing and additional sheathing on the exterior of the rigid insulation as a nail base for the fiber cement. I expect to use some type of rain screen between the new sheathing and the fiber cement.
The existing wall is 2x6 framing @ 24 inches o.c. with R19 fiberglass insulation and an interior polyethylene vapor barrier that must remain in place under the interior gypsum board.
XPS appears to be a better choice than EPS for R value, and 2 inches (R10) appears to be better than 1 inch to raise the temperature of the existing sheathing to limit the chance of condensation. Drying to the exterior may be slowed by the added rigid insulation and new sheathing.
Given the need to maintain the existing interior poly vapor barrier, what is the best approach to adding insulation on the exterior, minimizing moisture related issues, and supporting the relatively heavy fiber cement?
Thanks for considering this question.
Posted Sun, 02/09/2014 - 13:46
Edited Mon, 02/10/2014 - 08:05
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