Insulating this tricky space.

[24PoW]

Any advice on what technique/materials to insulate this awkward space? It's in the eaves and this space is pretty much all there is between my neighbour's and I.

 

[jacko555]

Hard to see whether the wall is flush with the rafter...

Really cheap and simple: wedge /fold loft insulation to close the gap.

Or

Fix plasterboard/ply to the wall closing the gap. If this leaves a gap by the rafter, affix a bit to the rafter to close the gap.

Once gap is closed - up to you. Maybe closing the gap is enough. Or take your pick of insulation materials

 

[^woody^]

Any insulation in an area separating properties would tend to need to be Rockwool, and all gaps sealed for flame and smoke