How many inches R49 blown insulation requires depends on the material type because different materials have different R-values per inch. For blown fiberglass, which has about R-2.5 to R-2.8 per inch in loose-fill form, R49 typically needs 16 to 18 inches of depth when installed at the manufacturer's specified density. For blown cellulose, which is denser and has about R-3.2 to R-3.8 per inch, R49 typically needs 13 to 14.5 inches of depth. For blown mineral wool, which is about R-3.0 to R-3.3 per inch, R49 needs roughly 14 to 16 inches. These depths assume proper installation without compression and at the correct coverage rate listed on the bag. It is critical to not just measure depth but also check that the correct number of bags per 1000 square feet was used, because fiberglass that is fluffed too light may look thick but will not achieve the stated R-value due to low density and air pockets. Always use rulers placed in the attic to verify average depth in multiple locations and follow the manufacturer's chart for both depth and bag count to ensure warranty and energy code compliance.
1 votes
Marked as accepted