How to tell how thick your roof insulation is
Take a ruler or tape measure up into your roof space. You can usually do this safely standing on a ladder and peering into the ceiling hatch.
Insulation that doesn't meet HomeFit or Healthy Homes Standards – this shows less than 120mm thick (or R2.2). This can be confirmed by an assessor, by installers receipt or by label stapled in the ceiling. To be HomeFit Plus standard, insulation would need to be R3.6 (R4 in Zone 3). Higher levels of insulation are recognised with additional points.