The rigid insulation method requires the utilisation of 150mm thick insulation in between the rafters along with a 50mm air gap in order to avert cold bridging.
Insulating attic dormers.
Loose fill or batt insulation is typically installed in an attic.
In case the space on the existing rafters is not enough you can fix a batten to the rafters underside in order to enhance the depth.
Loose fill insulation is usually less expensive to install than batt insulation and provides better coverage when installed properly.
If the attic kneewall spaces are used for storage then you ll have to insulate along the roof slope down to the eaves and create an air barrier at the rafters.
See more on different types of insulation.
Hold the cut insulation against the dormer walls with the paper side facing the attic or room and the fibreglass facing.
Put on a long sleeved shirt safety glasses and a dust mask.