I have just cleared out my extensive loft area, removing a lot of patchy very thin rockwool, vermiculite, bits of carpet etc. The loft is of a very complex, multilevel construction as our house has had two different extensions. There are some bits with 100mm joists, some with 200mm joists, some areas have 200mm joists with 100mm joists on top at right angles. Most of the roof is at a very low pitch, and I won't be able to achieve much thickness at the eaves.

I want to insulate effectively up to 300mm, but using batts or rolls will be very difficult in some areas. I may need to use a combination of fibre insulation and loose fill.

How should I approach the job? I was thinking about using warmcel up to the top of the joists (so in some areas it would only be 100mm deep) then cross laying batts to get the thickness up.

I'm also concerned about natural insulation and mice - we always have a lot of mice in the winter, I've heard they just love to nest in the likes of thermafleece/warmcel, is this true?

Quilt is going to be easier cheaper and better than batts. Lay in in perpendicular layers. 300mm in total is a good idea too.

Homotherm is a batt insulation made from cellulose(paper) it was distributed by construction resources until they went pop.

If your roof is not otherwise ventilated or you use tyvek then you would need to allow 50mm of ventilation at the eaves.
However by pack out what I meant was to pack it in such a way as to create a barrier to prevent the warmcell spilling out of the eaves so that you can fully fill the eaves.

The other way would be to fix scrim material up the rafters to protect the ventilation route and then blow in warmcell to a depth of 300mm and the scrim will stop the warmcell being blown out or blocking the ventilation.