Ceilings and roofs

Ceilings and roofs

BASIX recognises the following roof types:

Flat ceiling and pitched roof

  • Pitched roof (slope > 10°) with roofspace 
  • Flat/horizontal ceiling

Raked ceiling / Pitched or skillion roof

  • Pitched or skillion roof (slope > 10°)
  • Ceiling lining parallel to roof

Flat ceiling / Flat roof

  • Flat roof (slope ≤ 10°)
  • Flat/horizontal ceiling


Tip: Providing roof insulation will reduce your ceiling insulation requirements.


Cross section of a new dwelling underneath an existing dwelling


If your dwelling has another dwelling above (such as a granny flat), you are not required to describe the ceiling and roof type. If the dwelling has part of the ceiling with a dwelling above and part with a roofspace above, describe the ceiling with a roofspace above only.

Roof insulation

Providing roof insulation will reduce your ceiling insulation requirements.

Be sure to select the applicable roof insulation for each roof type that you have nominated. You must select roof insulation if you have a medium- or dark-coloured roof.

If you have a roof with a low solar absorptance it may not require roof insulation, however you can still choose to install roof insulation and reduce your ceiling insulation requirements.

You will also need to check that the selected (or required) roof insulation fits within the available roof space. Any foil product under the roof will require an air gap of at least 20mm between the under-side of the foil and the top of the ceiling insulation, as shown in the diagram below. The insulation must be installed in accordance with the relevant provisions and Australian Standards specified in the NSW additions to the Building Code of Australia (BCA). 

Example: Insulation in a skillion roof with raked ceiling, with metal deck roofing and foil-backed blanket over purlins/battens, 20mm air gap between the roof blanket and ceiling batt, ceiling insulation batts and plasterboard.