Passive Design

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

Insulation

Specifying high levels of insulation for the thermal envelope is at the heart of good passive design.

Insulation acts as a barrier to heat flow, reducing heat loss in winter to keep the house warm or reducing heat gain in summer to keep the house cool. Inadequate insulation and air leakage are the main causes of heat loss in homes.

The most economical time to install insulation is during construction. Retrospective installation may be more difficult and costly. However, there are options for improving insulation in existing homes.

Insulation is needed in the ceiling, walls and floor. The key choices to be made are:

  • the insulation format (blanket, rigid or loose fill) and material (for example, glass-fibre, wool, polyester) used in each part of the building, and
  • the amount specified to achieve the desired R-value (that is, the desired level of thermal resistance).

The format and material specified will depend on client preference, the type of construction (for example, timber frame or concrete), and on which part of the building envelope is being insulated.

For a house to have zero or near-zero space heating needs, aim to achieve the following  insulation targets, measured in construction R-values. The lower R-values are for warmer parts of the country:

  • Floor -
    • fully insulated concrete slab, with continuous horizontal insulation underneath (most pod/raft style slabs do not have this) and perimeter insulation, or
    • timber floor of about R3.0 (depending on construction and product). For pole houses, the insulation levels should be at least the same level as the walls.
  • Walls - about R3.6 for low-mass construction (such as timber framing and cladding) and R3.0 for high-mass construction (such as concrete floors and walls)
  • Windows - about R0.4 to 0.53 (for example, with thermally-broken, aluminium frames with low-e glazing).
  • Roof - about R4.6-5.5

When specifying insulation materials, the key consideration is the thermal performance of the material over the life of the building. Also consider the sustainability of the insulation material for example, the emissions associated with its manufacture. For details, see our insulation materials factsheet(PDF) and the materials section of this site. Some thermal insulation products have qualified for the Environmental Choice New Zealand label

Also see glazing and glazing performance for information about thermal insulation in windows and glazed doors.

Rental property owners should know that thermal insulation (where it is reasonably practical to install it) has been a legal requirement in privately-owned rental homes since 1 July 2019. The general rule requires ceiling insulation of R 2.9 for properties in zone 1 or 2, and R 3.3 for properties in zone 3. Ground floor suspended floors must have insulation of at least R 1.3. (There are special rules for ceiling insulation originally installed before 1 July 2016.)

It has been a requirement since 1 July 2016 for landlords to disclose in new tenancy agreements the extent of insulation in their rental properties.

Healthy homes standards

The Government introduced updated insulation requirements for rental housing in the healthy homes standards announced in February 2019.

The standard does not require anything more from landlords who have installed insulation to meet existing 2016 insulation requirements.

The healthy homes insulation standard affects a new group of rental homes that already have around 70120 mm of ceiling insulation and were not required to retrofit insulation under the 2016 requirements. These homes will now have to top-up the insulation to a minimum 120 mm.

The healthy homes standards will apply to new tenancies from 1 July 2021 and to all rental homes from 1 July 2024.

Curtains and blinds

Curtains and blinds can also play a significant role in keeping a home warm in winter. Many homeowners will be familiar with thermal curtains, where an acrylic coating is bonded to the back of the fabric. Heavy lined curtains actually made better insulators than thermal curtains in testing by Consumer New Zealand, however. The best curtain performance comes from those that are floor-length. With blinds, those that have a honeycomb structure with pockets of air trapped between the front and back faces of the blind are the best insulators.

 

Updated: 1 July 2019