I have gotten a lot of different advice on this project, hoping I can get some professional comments here.
I live in Northern California so weather goes down to freezing in winter, into the 90's in summer. I purchase a house that the front section was built as a 1931 vacation cabin. In 2000 an addition was added.
The older section has a large main room with a vaulted ceiling, looks like 1x6 redwood planks running long way. But it appears the shingle are then on top of that, so no cavity of any kind for insulataion. Even now when the weather is in the 60's, if the sun is out, the redwood on the inside measures up to 104 degrees and beats down on the room like an oven.
The plan is to remove the shingles and built a 2x4 frame to go over the redwood and fill with 3.5" thick solid polyiso board insulation givng me an R of about 24. No ventilation planned.
So my roofer says we still need a venting path and a ridge vent which means I give up insulation thickness and R rating, or we move up to 2x6 and add more added cost and weight.
So I am looking for comments on:
1) venting or no venting?
2) vapor barrier or not, and where does it go
3) any heat reflective foil and where?
4) Does an engineer need to look at load bearing issues with added roof?
5) Any comments on codes for California Bay area would help.
I have attached a photo of the inside of the roof with the loft where I have been able to measurements.
I also included a photo of the roof from my neighbor's roof. There are 4 areas.
1) Vaulted main area
3) Flat section
4) 2000 consruction which is fine and will nto be touched.