Replies

1. GBA Editor
   Martin Holladay | Jun 26, 2017 04:50am | #1

   Beach 13,
   The insulation method suggested by your insulation contractor is a violation of most building codes. (Cellulose is defined as an "air-permeable insulation," a type of insulation that can't be installed between rafters unless the builder provides a ventilation space between the top of the insulation layer and the underside of the roof sheathing.)

   While it's true that moisture accumulation problems are worse in very cold climates than mild climates, I still don't recommend the approach you are describing.

   For more information on this issue, see Insulating Low-Slope Residential Roofs.

2. 
   charlie_sullivan | Jun 26, 2017 07:36am | #2

   Martin's answer is a good conservative one. But in Southern California, it is less risky than in somewhere that gets colder. How risky it is depends on the specific of your local climate, which we could comment on better if we knew your location more specifically, e.g. a zip code, and also depends on how air-tight your ceiling plane is. Unfortunately, a house built in 1975 is unlikely to have good air tightness ... and it sounds like it would be hard to get access to all the places you'd want to do air sealing.

3. 
   user-2310254 | Jun 26, 2017 09:45am | #3

   If your home is close to needing a new roof (and the roof line is relatively simple), installing rigid foam above the sheathing would be the best solution.