Passive Design

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

Installing insulation

The correct installation of insulation is critical.

On this page:

  • precautions when installing insulation
  • installing insulation generally
  • specific installation instructions

NZS 4246:2016 Energy efficiency – Installing bulk thermal insulation in residential buildings provides guidance on insulation use and installation so that thermal performance requirements and durability of the building envelope elements are achieved. NZS 4246:2016 is referenced in the Acceptable Solution H1/AS1.

Precautions when installing insulation

Take the following precautions when installing insulation:

  • Take extreme care where electrical cables run under the floor. There have been fatalities when the installer has put a steel staple through a live electrical cable and been electrocuted.
  • To be conservative, keep polystyrene separated from PVC-sheathed electrical cables. Over time, the cable sheathing will become brittle if these two materials stay in contact.
  • Do not allow insulation to get wet as this will reduce performance.

Installing insulation generally

When installing insulation:

  • follow the manufacturer’s recommendations for safety and handling
  • wear recommended protective clothing and masks.

Install insulation to:

  • fit firmly without edge gaps because even relatively small gaps can have a big impact. For example, a 16 mm gap around the edge of ceiling insulation can cut its R-value by almost half
  • cover newer types of recessed downlights that are labelled IC and IC-F but NOT older downlights in existing ceilings. Insulation must not sit over these older lights or touch the sides unless the fitting manufacturer can verify that this is acceptable.
  • be separated from fixtures that get hot, such as flues. A flue with no casing must be separated from heat sensitive material by four times its diameter. A flue with two casings and 25 mm air gaps between casings and flue requires a 25 mm gap. For a single casing, the separation would be 2 x flue diameter. (See AS/NZS 2918:2018 Domestic solid fuel burning appliances – Installation.)
  • have a minimum 25 mm air gap between insulation and flexible roof underlay in skillion roofs.

Specific installation instructions

Blankets and segments

Fit blanket and segment bulk insulation firmly between framing without gaps. They must not:

  • be compressed – for example, a 100 mm R 2.0 product compressed to 80 mm  will have its R-value reduced to R 1.6
  • have folds or tucks
  • sag within wall framing cavities – the blanket or segment should preferably be the same thickness as the cavity
  • be installed into timber framing that has a moisture content of over 20%.

Loose fill

Install loose fill insulation so that it:

  • cannot be shifted by air movement
  • is laid in an even thickness
  • is laid with sufficient depth to allow for settlement
  • is not compressed
  • is kept away from downlights.

Polystyrene boards

Rigid polystyrene board insulation must:

  • be laid over a damp-proof membrane when used under a concrete slab on the ground
  • be separated from internal spaces by a lining material
  • be fitted tightly against the underside of the flooring when fitted between floor joists
  • be fitted tightly between cavities
  • ideally,not come into contact with PVC (such as TPS wiring).

When used as a cladding, rigid board insulation should be installed in accordance with NZS 4246 and the manufacturer’s instructions.

Insulating plaster

Insulating plaster must be applied to the design thickness of the plaster mix and in accordance with the manufacturer’s instructions. When applied externally, it must be protected from the weather by a suitable weatherproof coating.


EIFS cladding systems are to be installed in accordance with the system supplier’s instructions.


Updated: 20 October 2023