Increasing the R-Value of an existing cathedral ceiling
When attempting to increase the R-value of a poorly performing cathedral ceiling, what is the most cost-effective interior application? There are exposed rustic wooden rafters every 4 feet or so that protrude from the ceiling 6″.
My thought was to apply 2″ rigid foam to the interior with 1X3 furring strips in between existing ceiling and the rigid board taking extra care to make the ceiling airtight prior to installation and then taking great care to make sure the rigid board is airtight with spray foam around perimeter and seams. Lastly, would be applying drywall to the rigid board.
The cheapest (and possibly the best thermal performing) method seems like it would be filling the large cavities between the exposed rafters with unfaced high-density fiberglass batts and then running the rigid foam board and drywall over the rafters. You would obviously lose the look and feel of the exposed rafters, but if the homeowner is willing to part with that look in hopes to achieve comfort and energy savings without paying out the wazoo for spray foam then wouldn’t this be a good option?
My main concern is moisture build up within the ceiling assembly. Would I want to use EPS rather than polyiso. Being in Ohio at that, where it is hot and humid in the summer and cold and dry during the winter it seems like let the ceiling breathe somehow would be important. The roof was replaced within the last couple years.
Thanks for any insights!
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