Home insulation plays a critical role keeping your home warmer, cutting heating costs, and improving energy efficiency. On this page you’ll find advice for retrofitting insulation in existing homes, as well as new builds.

Insulation improves energy efficiency

Insulation is one of the most effective ways to keep your home comfortable, healthy and warm, and can save you up to $340 each year on your power bills.*

Insulation works best when it forms a continuous thermal envelope around the home – including ceilings, walls and floors. In older homes, this can be harder to achieve, so it’s usually best to start with areas that are easy to access, or insulate when you are already undertaking other renovations.

On this page

The thermal envelope of your home 

The thermal envelope is what seals the warm (or cool) air inside your home and keeps the outside temperatures out. A well-designed thermal envelope is the key to year-round comfort and helps your heating and cooling systems work more efficiently. That means less energy wasted and lower energy bills.

Your home’s thermal envelope includes all of the components that provide insulation — like the ceiling, walls, floors, windows, and doors. To work well, these should form a continuous, gap-free layer around your home. Any weak spots (called thermal bridges) can let heat escape or unwanted air sneak in.

Ceiling insulation

Ceilings are often the easiest and most effective area of an existing home to insulate — whether you’re starting from scratch or improving what’s already there.   

Good ceiling insulation can make a big difference to your home’s comfort and energy use — so it’s a great place to start.

Top up your existing insulation 

If your ceiling already has insulation, it might not be working as well as it could be. Insulation settles and compresses over time, reducing its effectiveness.  

If it’s still dry and in decent condition, you can often add a new layer over the top. 

Signs that your insulation needs replacing or topping up: 

  • It is less than 120mm thick (or sits visibly below the level of the ceiling joists). 
  • There are gaps in coverage — even small breaks in insulation can let a lot of heat escape.  
  • The condition is poor — with dampness, mould or soiling from pests or leaks.

Wall insulation

Wall cavities are a key component of your home’s thermal envelope — but in existing homes, they’re more difficult to access than your roof space or under floors.   
 
This makes retrofitting wall insulation more complex, but still worthwhile for long-term energy savings and comfort. 

Retrofitting wall insulation 

It’s recommended to get a qualified professional to undertake wall insulation. It typically requires building consent and careful consideration of your home’s cladding, wiring, and moisture protection. 

The best time to add wall insulation is when you’re already opening the wall cavities – so it pays to time it with renovations. If you’re replacing your home's cladding, or internal wall lining, this is a great opportunity.  

If there is no building paper present, or it’s damaged, this should also be installed at the same time. This protects your insulation from moisture over time.

Underfloor insulation

Insulating the spaces between your floor and the ground is one of the easiest and most cost-effective ways to improve the comfort and warmth of your home. 

If your subfloor is more than half a metre off the ground, insulation can be fitted easily between the joists. It’s often worth doing at the same time as your ceiling. If there is existing insulation but it has slipped or has gaps, it’s time to replace it.

Insulating different sub-floor spaces 

New Zealand homes are built on a variety of foundations, with varying levels of access. This can make installing insulation tricky or affect the type of product you need to use for the job.  

  • Exposed subfloor spaces — Wind and weather can damage your insulation over time. To protect it, consider enclosing your sub-floor space (in line with the building code), or installing plywood or fibre-cement sheets to the underside of the floor after your insulation is installed. 

  • Enclosed sub-floor spaces — If your subfloor space is enclosed, installing a layer of polythene ground sheet on the ground under the house can help reduce moisture levels. The sheet will help the insulation work better and make your home healthier and easier to heat.

Understanding insulation types and R values 

The R-value tells you how effective insulation is compared to other options. The higher the R-value, the better it prevents heat loss during winter.  

Some materials are better at insulating, so can have a higher R-value without needing to be as thick. Others need to be thicker, or denser to achieve the same result. 

In New Zealand, any insulation product should be in compliance with AS/NZS 4859.1 standards and include safe handling instructions and performance guarantees. A professional installer can help you choose the right product.

Home insulation grants

Warmer Kiwi Homes offers grants of 80-90% of the cost of ceiling and underfloor insulation, and up to 80% of the cost of an energy-efficient heater, to eligible homeowners.

Other ways to improve your home

All the individual building blocks that provide insulation in your home (and make up the thermal envelope) need to be working together to form a ‘seal’ around your home — without any gaps.

  • Design for Energy Efficiency

    If you’re building new, or renovating your existing home, you can lock in energy savings from the start with good design choices.

  • Improve window insulation

    Windows are the biggest source of heat lost in an otherwise well insulated home —double or secondary glazing can make a big difference.

  • Reduce draughts

    Airtightness and insulation work together to keep your home comfortable, dry and healthy during the winter months — so it pays to seal up any sneaky draughts.