Passive Design

Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.

Options for roof insulation

Ceilings/roof spaces are typically insulated using blanket/segment or loose fill insulation, although higher-performance roof details may include rigid insulation.

On this page:

  • Timber-framed roofs
  • Steel-frame roofs
  • Access hatches to accessible roof spaces
  • Skillion roofs

Blanket or mat (segmented) insulation is available in glasswool (fibreglass), wool, polyester, wool/polyester mix, and mineral wool.

Loose fill insulation is available in glasswool, mineral wool, macerated paper and wool.

Rigid insulation includes PIR (polyisocyanurate), XPS polystyrene and SIPS (structurally insulated panels).

For information about performance, durability and environmental properties of each material, see our insulation materials factsheet(PDF) and the materials section of this site.

Minimum roof insulation R-values in the schedule method of NZS 4218:2009 Thermal insulation Housing and small buildings are R2.9 in climate zones 1 and 2 and R3.3 in climate zone 3. Going well beyond this minimum will make a much more comfortable home with lower heating requirements. For example, BRANZ calculations show that there is a clear economic case to specify R4 roof insulation in the lower North Island and R5 in the lower South Island.

Significant changes for complying with Building Code clause H1 insulation requirements are coming. From 3 November 2022, 5th editions of Acceptable Solution H1/AS1 and Verification Method H1/VM1 will apply, and the previous 4th edition documents will no longer be able to be used. Where building consent applications for housing are submitted before 1 May 2023, however, roof, wall and floor construction R-values can be equivalent to the previous (4th edition) requirements.

Timber-framed roofs

Install ceiling space insulation between joists over the ceiling lining where possible as this is where the greatest heat loss occurs. A second layer should be laid over the framing to reduce the effect of thermal bridging.

Steel-framed roofs

The general principles of roof insulation are the same for steel-framed roofs, although there are some slight changes required to where and how insulation is installed in practice for the best results. For more information see the BRANZ publication Building Basics Lightweight Steel Framing.

Access hatches to accessible roof spaces

Access hatches installed in ceilings to give homeowners entry to the roof space have commonly been a weak point in ceiling performance, by not being insulated and by having gaps in their construction that allow air and moisture to move from living spaces into the roof space. This moisture can potentially lead to condensation and mould problems in the roof space.

Proprietary access hatches that are both airtight and insulated are readily available. These are more likely to perform better than hatches made in the traditional way.

Skillion roofs

For skillion roofs with exposed rafters, install insulation over the ceiling lining between purlins purlins must be sized to provide sufficient depth for the required thickness of insulation plus a 25 mm minimum air gap between the insulation and the flexible roofing underlay.

For skillion roofs with concealed rafters, install insulation between rafters the combined rafter/purlin depth is likely to be sufficient to ensure that a 25 mm minimum air gap is achieved.

Note: For both exposed and concealed rafter skillion roofs, an air barrier must be installed over a timber-boarded ceiling to prevent air movement into the roof framing.


Updated: 21 July 2022