porch and bay window insulation
These are often small isolated areas of roof than can be quite a challenge to get right if moisture can get into them and then not be able to get out.
Where this risk is minimal cavity wall type insulation can just be blown into the cavity. If this is not feasible then either the ceiling needs removing or the tiles to get access.
Installing some form of ventilation to the outside from this space is recommended, indeed required in the British Standard informing the Building Regulations.
Blocking air paths from inside the house is recommended if installing ventilation into this space is not possible.
The porch or bay window roof is filed with expanded polystyrene loose bead insulation (such as ecobead)
Performance target : 0.2 W/m2.K.
Alternatively, underdraw internally with insulating board and replaster.
Performance target : 0.3 W/m2.K.
Further information is available in the Retrofit Pattern Book