I'm preparing to insulate my attic and need to know how much is necessary and how much weight the ceiling can support.
I live in San Diego (mild/warm climate). The house was built in 1969. Currently there's no insulation in the attic. I've airsealed, insulated the ducts, put in rafter vents.
Joist spacing is 24". Gypum board thickness is 5/8". I assume the ceiling, like the walls, is nailed not screwed in.
My plan was to blow in 15" of cellulose to get me around R-49. My concern is the weight of the insulation could cause the ceiling (original, as far as I can tell) to bow. The table for the insulation shows the "Minimum Weight" for R-49 is 1.591 lbs/sqft:
- R-13 0.34 lbs/sqft
- R-19 0.519 lbs/sqft
- R-22 0.613 lbs/sqft
- R-25 0.710 lbs/sqft
- R-30 0.878 lbs/sqft
- R-38 1.164 lbs/sqft
- R-49 1.591 lbs/sqft
- R-60 2.059 lbs/sqft
For the weight gypsum can support I found this link which quotes weight limits:
1.3 lbs/sqft for 1/2" sheetrock w/ 24" framing
2.2 lbs/sqft for 5/8" sheetrock w/ 24" framing
How much insulation could my ceiling support w/o risk of bowing?
Is R-49 even warranted in this mild climate?