Increase of R value of fiberglass by enclosing cavity
user-7049627
| Posted in Energy Efficiency and Durability on
Garage ceiling with two layers of 3.5″ fiberglass, top layer with paper toward floor bottom layer stapled with paper down to 2″ x 8″ joist. How much would the R value increase of this assembly if the garage ceiling was sheet rocked with 3/4″ sheet rock?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Bert,
It might be helpful to know your location. Can you share? You also might want to read this article on insulating a cold floor: http://www.finehomebuilding.com/2012/03/08/how-to-insulate-a-cold-floor
Not much, but you might get a significant reduction in air leakage.
Much more if you added rigid foam then the sheet rock.
Bert, fiberglass doesn't do well against air leaks, or against large temperature differentials from one side to the other (because convection currents can form within the fiberglass). Although the down-facing kraft paper slows air movement to a degree, you would find some improvement with sheet stock, sealed as an airtight layer. In a garage you shouldn't have exposed kraft facing anyway, because it is flammable. Like Jon said, you would see even more improvement with rigid foam.