New Pitched Roof Insulation

[Aszabo]

Hi! Wondering if someone can give me some insight into the insulation of our new clay tiled roof. We plan on putting 8 to 10 cm PIR above the rafters and 15 cm of rockwool insulation between the rafters. My questions are:
1. Will that be enough insulation to keep the loft area comfortable (recommendation was 25 cm on the inside and 5 cm on the outside but we would like to maximize our headroom in the loft area as it will serve as an office/guest room).
2. The PIR that we are in the process of purchasing is faced with aluminum on both sides and which our roofer is not a enthusiastic about. He's worried that on the inside there will be moisture issues. Has anyone dealt or had issues with this? The last thing we need on this project is yet another problem since our original contractor ran off leaving a shody half done roof that now needs to be redone.
3. I'm also interested in knowing how the layering of materials would look on such a hybrid installation to avoid moisture issues.

Thanks.

 

[Deluks]

Your roofer doesn't sound very clued up about insulation.
You wouldn't normally insulate above the rafters, but underneath and in between, and using the same insulation throughout.

 

[noseall]

Your roofer doesn't sound very clued up about insulation.
You wouldn't normally insulate above the rafters, but underneath and in between, and using the same insulation throughout.

...unless it's a warm roof.

 

[noseall]

We plan on putting 8 to 10 cm PIR above the rafters

Why are you opting for 'warm roof' positioning of the the insulation, i.e. on top of the rafters? Its reasonably straightforward to vent a pitched roof.