Expert: Dave Johnson - 6/10/2008

Question
Dear Sir: I live in LA, CA want to build an addition room with cathedral ceiling:
1. Recommended Insulation materials
2. Need vapor retarder?
3. Need Radiant Barrier?
4. Need Air space?
5. Rafter size
6. How to insulate cathedral ceiling?
Thanks!

Answer
Hi Dave,
First, I need to tell you that i am in Maine... and am not overly familiar with building methods there in Ca.
However, In answer to the question re: air space and rafter size, I would use as deep a rafter as possible, to allow a good rigid foam insulation and an adequate VENTED air space above the foam. ( You can
vent the space by using a ridge vent and soffit vents)
This will take the warm air from the space and allow it to flow...thereby cooling it somewhat.
As far as the walls, i personally DON'T like fiberglass... its just a $%^& filter and over-rated as an insulator.
Spray-on foam is used here in walls often, as is rigid foam with
crack filler.


Best of luck!

Dave J