How much does it cost to insulate a house in New Zealand?

Realestate.co.nz asked 1,200 homebuyers which features were most important when searching for a house. Apart from orientation to the sun, the results found that good insulation and warmth were the top priority for house hunters. Almost 90 per cent of respondents who were selling or had recently sold their homes said that environmental factors such as efficient energy, water and heating could contribute to a property fetching a higher price.
So the first steps when doing up your home should be to make it warmer, drier, more energy-efficient and kinder to the environment. Insulation has been rated as the second most important feature of a home by potential homebuyers. For an average three-bedroom, 100m2 house you can install ceiling and underfloor insulation from $3,000 to $5,000 (ceiling and underfloor depending on grade, joist sizes and the installer).

Do I need insulation?

In a word, YES! Insulation may not be the sexiest of renovation topics but its importance in the overall success of a new build or renovation cannot be overstated. It should be the first priority. Getting the right insulation into the ceiling, underfloor and behind the walls ensures ongoing savings to heating and/or cooling bills and helps reduce greenhouse emissions in the process.

Where does thermal loss occur?

The ceiling and roof accounts for a sizeable chunk of heat loss in a home -around 40%- while walls can lose about 24% of heat depending on the amount and kind of glass they have. Factor in a further 10% heat loss through floors and you can see why insulation is critical to achieving a warmer, dryer home. New Zealand homes built before the late 1970’s will probably only have minimal existing insulation in the ceiling, possibly none in the walls and what remains may have settled and / or be full of gaps.

What are R-Values?

All insulation types in New Zealand are given an R-value. These are a measure of thermal resistance IE: that is how well a product resists heat flow. The R-value is governed by the material used, its density and thickness. The higher the R-value the more effective a product will be and this will be reflected in the price too. Products that share the same R-value should perform equally well if installed according to code and to the supplier’s specifications. 

In New Zealand R-values differ in the regions:

R- values for the North Island excluding the Central Plateau:
Ceiling R3.2, Walls R2.2 and Floors R1.6.
On the Central Plateau and in the South Island:
Ceiling R3.6, Wall R 2.4 and Floors R1.6

What other factors should be considered?

Beyond R-values, soundproofing, dust-free environments (for allergy sufferers,) eco-friendly options or specialised products like loose fill for inaccessible ceiling areas will affect insulation choices.
The overall thermal efficiency of a home is not just limited to out-of-sight products either, windows and frames with high R values, thermal drapes and in the right situation, thermal mass, can all work together to create an energy efficient year-round comfortable home. New Zealand is a country full of micro-climates, the effects of each impacts on houses in varying ways. Speak to a Refresh renovation consultant about how to tailor the correct balance of insulation, glazing and thermal mass to maximise the position and fixtures of your home.

Do I need a consent to retrofit insulation?

In New Zealand, no building consent is required for retrofitting ceiling or floors insulation. When it comes to retrofitting insulation in external walls you are required to have a building consent. The use of foil as an underfloor insulation has now been banned for repairs or retrofitting. Historically foil was often not installed properly so was ineffective from the start. Moreover, foil acts as conductor for electricity and can become live if in contact with a live circuit. If foil is present, the power supply will need to be disabled before dealing with it. 

What do I need to be aware of behind the wall and ceiling lining?

A renovation consultant will always check for leaks, the condition of existing building paper and electrical wiring. Ideally insulation should be as thick as your wall cavity is deep or thicker than the height of the ceiling joists (IE: 120mm) and it should cover the whole ceiling, with the highest R-value possible.  “Insulation needs to be installed correctly to be effective,” says Refresh Renovation Consultant, Jim Gleeson. “It is important that there be no gaps and no ‘crushing’ of the insulation material. Any leaks must be fixed prior to insulation being installed to avoid growth of mould inside the insulation.”

What are my insulation options? (NZ)

Ceiling

Even if your ceiling has pre-installed insulation you may need to top-up. The most common ceiling products are polyester made from recycled plastic bottles and fibreglass (glass-wool.) Bulk ceiling insulation comes in segments that will fit between the joists above your ceiling, or in blankets that can be rolled out across the top of the joists to compensate for heat loss through the timber. Always aim for higher R-value insulation.
If older recessed downlights are a factor then a safety gap around each fitting may be required. Jim says, “Many contemporary LED downlights can have insulation laid directly over them removing unwanted gaps and heat loss. In this situation, a notification label will need to be installed in the entrance to the ceiling space.”
If attic crawl space is an issue then Loose fill insulation is an option. Depending on the product and the installer loose fill performance, effectiveness and durability tends to be variable. 

Underfloor

The most popular choices of bulk underfloor insulation are made from polyester, wool, polystyrene or fibreglass. The most critical factor for installing all products is ensuring that there is no air gap between the bottom of the floor and the top of the insulation. Foil was once considered a cost-effective option and is still found in many older homes today. However due to issues around safety and its reduced performance, foil will need to be replaced with a bulk insulation option.

Walls

As with ceilings, bulk insulation for walls comes in pre-cut segments or as blanket rolls. To install bulk insulation into an existing wall either the lining or cladding will need to removed. “If access into the external walls is difficult or expensive,” says Jim, “you could think about adding a layer of high density plasterboard over the walls and repainting inside, this may be enough to make quite a difference and reduce external noise as well.”
‍

Pricing in New Zealand

Ceiling

For product and install of R2.9 - R3.3 ceiling insulation on a 100m2 house, the price ranges from $1,500 - $2,500. This is dependent on ceiling space, access and R rating selected. In some older houses or houses with gabled ceilings (ceiling that follow the shape of the roof) the only access for insulation is by removal of the roofing material.

Underfloor

For product and install of R1.3 - 1.6 underfloor insulation on a 100m2 house, the price ranges from $1,500 - $3,000. The price will vary depending on type, R value and ease of access under the house. If there is less than 400mm from floor to bare ground, it is recommended to install a layer of polythene over the ground to stop rising moisture. To get a ground moisture barrier 250mu installed for a 100m2 house, the price sits around $1,000 - $1,500.

You might be interested in reading: Insulation options.

 

Get in touch with Refresh to discuss your home renovation project

If you would like to discuss home renovation options for your next renovation project, please use the enquiry form on this page to provide us with your contact details. We will get in touch with you at a time that suits you to discuss your project. If you would like to provide us with more information about your project, we have a more comprehensive enquiry form on our "Get in touch" page too.

*Costs are rough estimates and are subject to change. For a fixed-quote accurate to your specific project, please consult your local Refresh Renovations specialist. All Refresh Renovations franchises are independently owned and operated.