How much insulation is R6.6?

The new requirement for residential roofs is R6.6. This is an installed construction value which includes reduction for framing and thermal bridging.

Here are some of the nominal (i.e. just the material) insulation thicknesses:

  • Glass / polyester / mineral fibre batts – R6.6 is roughly 320mm of insulation
  • Polyisocyanurate (PIR) – 120mm
  • Rockwool semi-rigid insulation – 225mm

To account for the thermal bridging, you might need to increase this by 25-75% depending on the bridging. This would leave something like:

  • Glass / polyester batts – 400-600mm
  • Polyiso – usually continuously installed – 120mm
  • Rockwool rigid insulation – usually continuously installed 225mm
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