Insulation Basics

Most New Zealand homes are under-insulated. Installing insulation is now a very technical area as incorrect installation, creases, folds or gaps in your insulation can reduce it’s effectiveness up to 50%


  • The NZ Standard for installing insulation is NZS 4246:2016 Energy efficiency – Installing bulk thermal insulation in residential buildings.
  • Research shows that damp, mouldy, poorly ventilated homes affect the respiratory health of many New Zealanders.
  • To help address these issues, MBIE has introduced the new 5th edition of H1/AS1 and H1/VM1 for housing and H1/AS2 or H1/VM2 for buildings greater than 300 m². This means significantly more insulation will be needed in the ceiling, walls and floors of new buildings from 1 May 2023.
  • Insulation creates a barrier that slows the transfer of heat from the inside of your house to outside. It is the most effective way to keep your house warm.
  • A well-insulated house requires less heating (or cooling) to maintain a given temperature.
  • Many houses were built before insulation was widely used or made compulsory in 1978.
  • Insulation levels required by the NZ Building Code are decades behind European levels.
  • Ceiling and underfloor insulation has been compulsory in all rental homes since 1 July 2019. The healthy homes insulation standard builds on the current regulations and some existing insulation will need to be topped up or replaced.


In this information you will find tips on how to insulate your home and make your insulation dollar go as far as possible.

Two-thirds of current New Zealand homes were built before 1978 when it became mandatory to install insulation.This means two-thirds were built with hollow walls clad with weatherboards, bricks or sheeting, single-glazed wooden-framed windows and generally wooden floors over piles. Making a pretty leaky house that is hard to heat. Insulation can go a long way to keeping your home warm and your power bills down. It makes for a healthier environment, reducing colds and other respiratory illnesses by helping to eliminate condensation, dampness and mould.


Where your heat goes: If your house has no insulation, about a third of heat is lost through the roof, another third disappears through windows, with the final third vanishing through the floor, the walls and through air leakage.


The ceiling space should be your first area to insulate – it is the easiest, most accessible area of your house to insulate and gives the biggest bang for your buck! Even if you have some insulation in your ceiling it is worth checking it is still performing. If it is an older type of insulation it is likely it has settled and is performing to a much lower standard to what we would do today. The best way to insulate accessible ceilings is with one layer between the joists and a second layer perpendicular and over the joists with blanket insulation.

Note that recessed ceiling downlights are a source of heat loss – air moves through gaps around the bulb, and insulation must be kept well clear of them due to the risk of fire, unless they are specially rated. Ideally downlights should be replaced with a ceiling light or they can be swapped out with LED (Light Emitting Diode) downlights rated to be abutted and covered with insulation

Floors and walls

Floors are relatively easy to insulate, provided there is reasonable access. Between 12% and 14% of heat loss is through the floor. Gaps in floors leak heat. Even small gaps can have a big effect. Installing your own underfloor insulation is possible, though not always advisable, because electrical cabling is sometimes laid between floor joists. For a long time, foil was the most common type of underfloor insulation. Due to the risk of electrocution retrofitting or repairing foil is now banned under the Building Act.


At the same time as installing insulation it is worth installing polythene on the ground as a moisture barrier. Even ground that feels dry about 40L per day of water can be released from the ground under a 100m2 house.


Insulating existing walls is difficult due to the internal lining or external cladding having to be removed first. If renovating, the method that we strongly recommend is removing the old wall linings and installing insulation. Also replace the building paper if missing – see detail in NZS4246. Target south-facing walls, which do not get sun and may also be hit by cold winds.

Please note that a Building Consent is required for work involving wall insulation due to bracing and weather-tightness issues that may result. Talk to a qualified builder or building officer for more information.


Uncontrolled draughts can lead to considerable heat loss. Sealing up most draughts can be easy and inexpensive.

Fit self-adhesive weather strips around windows and strips and draught excluders around and under external doors.
Seal up openings such as unused cat doors and open fireplaces. Get some draught ‘sausages’ to lie against the bottom of doors.

Product Options

If possible always insulate to a higher level than the New Zealand Building Code as it is a minimum. The extra cost in Insulation will mean lower power bills and greater comfort and most importantly improved health of the occupants. R-value refers to the resistance of the insulation, therefore the higher the R-value the more heat it stops from escaping. Choose a product that both suits your needs and has as high as R-value as possible.

Your choice of insulation types includes insulation installed as a blanket, segments or loose fill. It depends on where you use the product to what type is most suitable for the situation, eg segments for your walls that fit between the studs. There are also different materials, such as polyester, fiberglass, wool etc.


Before deciding on an insulation product here are some points to consider:

Does it lose effectiveness if it gets damp?
Will it eventually ‘settle’, that is, slowly collapse, and become less effective?
Is exposure to it hazardous to your health?
Has an independent body such as BRANZ appraised or endorsed it?
Is it recyclable or biodegradable in a landfill?
Is there a guarantee?
What is the expected lifespan?

Quality installation of insulation is important in all areas of your house – a gap of 5% can result in a 50% loss of the potential insulation effect in the immediate area of the gap.


Subsidies are available through the Warmer Kiwi Homes scheme (see

Determining insulation requirements

The minimum levels of insulation required for Building Code compliance can be determined using any of three methods, depending on factors such as construction type and glazing area. Specifying better than minimum is strongly recommended.

The three options are

  1. Schedule method
  2. Calculation method
  3. Modelling method

Insulation for new housing must comply with the New Zealand Building Code (NZBC) clauses H1 Energy efficiency and E3 Internal moisture. Professional assistance is required to work out which option is best for your property.


Please note that the information provided in this article is based on general guidelines. To obtain accurate Insulation R-values for your specific new build project, we recommend consulting insulation experts and local building codes.