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A well-insulated home will provide year-round comfort, and cost less to cool and heat. Insulation also helps reduce noise levels and condensation.

Many New Zealand homes are cold, damp and expensive to heat. About half the homes in New Zealand have adequate ceiling insulation and half have no floor or wall insulation.

These homes aren’t just uncomfortable to live in; they’re also bad for you. A Wellington School of Medicine study has found that families in un-insulated homes had more medical and hospital visits for respiratory conditions, and more days of work and school than those in insulated homes.

There are legal minimum requirements for insulation in new homes and additions to existing homes, but it’s worth spending a little more to exceed these requirements and get a warmer, more comfortable home.

While there are no specific requirements for existing homes, installing or upgrading your insulation is one of the best investments you can make.

Insulation performance

The measure of insulation is expressed as an R-value, which is a product’s resistance to heat flow. The higher the R-value the more effective the insulation is in resisting heat transfer.

The most common R-value in new homes for walls and roofs is between R1.5 and R3.0. Higher R-values are required in colder parts of New Zealand, although you can install higher R-values than the required legal minimum for more comfort and energy savings.

Where to place insulation

Most New Zealand homes are built of timber framing, which is good for earthquake resistance but poor at retaining heat. In an un-insulated timber house (pre-1978), two-thirds of heat is lost through the ceiling and exterior walls.

The most heat is lost through the ceiling and roof, so that should be your top priority for insulation.

The design and construction of your home will affect the specific types of insulation you can use, and where the insulation can be placed.

Some construction systems, such as aerated concrete blocks, hollow glass blocks and straw bales are more effective at retaining heat, and relatively little additional insulation may be required.

Roof and ceiling insulation

Roof space and room ceilings work most e4ffectively if they are all insulated together. About 42% of heat loss from an average un-insulated home occurs through this area (up to 60% in pre-1978 houses).

Use reflective insulation under the roof timbers (if accessible) and bulk insulation such as fiberglass, polyester or wool batts in the ceiling. Rolling bulk blanket insulation across ceiling joists is the most effective way to insulate the ceiling, as it covers the ‘cold bridges’ of the timber joists.

Wall insulation

About 24% of heat from an un-insulated timber home is lost through the walls. Walls can be more difficult to insulate than ceilings, particularly in existing homes.

If you’re using a framed construction system, insulation should be placed within the wall framing. Insulation can also be installed outside the framing (but the insulation must be weatherproof to be effective).

The amount of insulation you can install may depend on the thickness of the walls and the size of the framing. If you’re building a new home or major extension or renovation, consider increasing the framing size to fit in more insulation.

If you’re using a solid construction system such as concrete, insulation should be placed on the outside of the solid wall. The inside of the wall can also be insulated, but is less effective.

Wall insulation can be fitted to existing homes by:

  • Removing wall claddings and installing blanket or batt insulation—the best option for timber frames
  • Fixing solid or blanket insulation to the outside of solid walls. This will include external cladding as part of the system.

Floor insulation

Up to 20% of heat loss occurs through the floor in un-insulated houses. Under-floor insulation helps keep a home warm and dry. The most common material used is a double-sided reflective foil that is stapled along the floor joists.

Please note: It is best to use an approved installer because of the risk of electrocution if staples strike live cables.

Insulation should be used on the underside of suspended timber or concrete floors, or on the edge and underside of concrete floor slabs.

Polystyrene planks, which are cut to the width of floor between joists, are an effective and widely used type of insulation under timber floors.

Polystyrene ‘pods’ are available for concrete flooring, and expanded polystyrene insulation can be used in sandwich format between pre-formed concrete slabs and blocks.