Eaves insulation (again!) - The revenge of the soffit...

3 Jan 2013
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United Kingdom
Here is a crude profile picture of my eaves:

The pile of rockwool insulation in the middle of the pic is, I think, the missing insulation from between the rafters that have no insulation - where the wind has picked it up!!!
The 'wall' to the bedroom is one layer of foil backed plasterboard - can you believe that?
The insulation over the bedroom is 50mm block insulation - there is at least 5" of gap left above this insulation before the roof felt.

I want to use this area for storage but also keep the bedroom warmer

There is a huge gap between the top of the exterior wall and the bottom of the roof felt which allows the prevailing wind to freeze the house!
I plan to:

  • Add more insulation above the sloping insulation
    Add insulation to the dwarf wall
    Using wood, build the exterior wall up to the same height as the rafters, re-lay the displaced rockwool add as much more as I can and then board the area.
    Put a very small dwarf wall made of exterior 18mm ply above the exterior wall into the rafters leaving a 50mm gap at the top.
    Mount 100/150 mm deep baffles between the rafters butted to the roof felt about 100mm in from the very small dwarf wall.
    (My aim for these last two is to baffle the raging wind that screams through the soffits)
Firstly - are any of the parts of my plans foolish or have I missed anything obvious?

How thick should I aim to make the insulation above the sloping roof?
How thick should the block insulation be for the dwarf wall?

Thanks for reading!
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