Insulating behind existing attic/dwarf wall

[Robbie999]

I've just discovered a shocking lack of insulation in my 16 year old house built by Hopkins Homes.

It is a 3 storey house, where the top floor is a couple of rooms in the attic space with dormer windows to the front and back.
It has always felt cold but with energy costs reducing our central heating use it became obvious there was something seriously wrong.

Long story but I eventually cut an access hole in a dormer window recess to reval the true horror.

- Nothing but 1.5mm non-insulated plasterboard between the top room dwarf walls room and the eaves (roof tiles are only backed by black membrane)
- 1.6 metre strips of uninsulated ceiling for the rooms below at front and back of house
- Uninsulated microbore radiator pipes running through the voids.
- At least the sloping ceiling is backed by celotex type boards.

Space is limited and claustrophobic, and access behind the dormer recesses is only by arm's reach.
Joists are not regularly spaced - 50cm, 56cm, 40cm, 35cm etc .
So handling and using roll insulation would be hard.
I've opted for loose fill Thermofloc for the horizontal insulation.

But what can I use for the vertical insulation between the dwarf wall studs?
The studs are irregularly spaced, they are backed by a second layer of framing plus cross braces.
The vertical height to be filled is 1.6m
Again, handling rolls, cutting to size etc in that space while dealing with all over protection isn;t practical and does not appeal.
Cutting celotex boards to custom sizes and getting them in the spaces doesn't seem practical.
Are the type of slabs for cavity insulation suitable? Can they be easily cut and stacked to fill all areas?
Any other suggestions?

 

[cdbe]

I used dritherm 32 (high performance cavity batts), a bit more rigid than standard batts and easy to wedge in and cut with bread knife. I would fill to the top of your joists with loose fill then roll some (as much as possible) mineral wool on top (and covering the pipes if possible). You should try to address the thermal bridging of the vertical studding - depending on access, something like strips of 50mm PIR a few inches wider than the studs pinned to the back of the studs, which will also stop the batts falling out of the back.