Home Insulation Buying Guide

The government's home insulation bungle has demonstrated the importance of knowing what's what.
 
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01 .Home insulation

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In brief

  • Insulating your roof or ceiling will help keep your home a pleasant temperature, save you money on energy bills, and pay for itself over time.
  • Several different materials are available — the best one for you depends on your particular circumstances and preferences.
  • With non-renewable energy resources dwindling, insulation is even more crucial nowadays, and mandatory if you’re building a new home — see Mandatory energy ratings.

How insulation works

Heat always travels towards cooler areas. Insulation works by reducing the amount of heat entering from outside your home when it’s hot, and trapping warmth inside when it’s cold outside. The highest percentage of heat transfer occurs via the roof and ceiling, so it’s most important to insulate here. Insulation materials work by affecting some or all of the below three ways of heat transfer.

  • Conduction is the direct transfer of heat through solid materials. A metal poker put into a fire is heated through conduction.
  • Convection involves the transport of heat via the movement of gases or liquids. You’ll feel convection taking place in a two-storey house — the heat rises from the lower floor to the top.
  • Radiation is the transfer of heat across space from a warm body to a cold one — an example is the heat emitted by a bar radiator.

Materials

Insulation can be grouped into three categories:

Bulk

Bulk insulation contains fibres that trap tiny pockets of air, which resist heat flow because these air pockets are poor conductors.
Types of bulk insulation available include:

  • Glasswool. (fibreglass)
  • Rockwool*
  • Natural wool* (often mixed with polyester)
  • Polyester*
  • Polystyrene boards
  • Loose fill (made of shredded or granulated material)

Some examples are:

  • Cellulose fibre (made from recycled paper)
  • Natural wool
  • Granulated rockwool

* All come as batts or blankets.

Reflective

Reflective insulation dramatically reduces infrared radiant heat transfer from a hot surface to a cooler one. It's available as:

  • Foil sheets laminated onto paper
  • Concertina-style foil
  • as a multi-cell foil product (silver batts) — a structure made of two to four layers of foil with air spaces in between
  • To reflect heat, foil insulation needs to face an air space of at least 25 mm.

Composite

Composite materials combine elements of the two other types.
These include:

  • Batts or blankets with foil backing (foil side facing out)
  • Foil-faced boards

Which is best?

While manufacturers of each type tend to talk up their product, experts say any insulation is preferable to none, and every material has its place. The product chosen usually depends on personal issues, such as:

  • Price
  • Whether it’s made from recycled material
  • Where the insulation is being installed
  • Who’s doing the installation (DIY or professional installers)
 
 

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Glasswool and rockwool batts and blankets
Natural wool
Cellulose fibre
Boards (extruded polystyrene or expanded polystyrene)
Polyester
Reflective foils

Glasswool and rockwool batts and blankets

Glasswool is made largely from recycled glass. The Insulation Council of Australia and New Zealand (ICANZ) says its glasswool is 80% recycled waste glass, and its rockwool about 30-40% recycled building and slag waste.

Batts are inexpensive, easy to cut and fire-resistant. You can install them yourself, but make sure they don’t get compressed or wet, as this will reduce their R-value (thermal resistance).

You also need to check they’re butted together firmly when installed, as gaps will dramatically lower their effectiveness.

Rockwool is denser than glasswool and a better sound absorber, so this may be a good choice if you’re looking to reduce noise. However, it’s generally more expensive than glasswool.

No evidence for health scare

The International Agency for Research on Cancer (IARC) has now confirmed there is no evidence to support previous concerns that these products were possibly carcinogenic in a similar way to asbestos: minute particles becoming lodged in the lungs.

Manufacturers also now produce glasswool and rockwool that are more bio-soluble than before, meaning that if you do happen to inhale some fibres, they leave the body more quickly. You’ll still need to wear protective clothing to install these products though, to avoid skin and respiratory irritation (see DIY).

Natural wool

Natural wool is sold as batts, blankets or loose fill. Experts say wool is a niche product in Australia although it’s more popular overseas. Batts are usually wool blended with polyester, which helps them keep their shape. It’s recommended you choose batts that are 70% wool as these are more likely to be fireproof.

In CHOICE tests in 1997, some wool batts failed fire-resistance tests, so ask for assurance that it’s been adequately tested, preferably to the more stringent British Standard 5803 part 4. Also check the insulation has been treated to permanently resist insects that can breed in unprotected wool insulation.

Wool is usually more expensive than other insulation. If used as a loose fill it must be thoroughly scoured and treated with insect repellent and fire retardant.

Cellulose fibre

Cellulose fibre is made from pulverised recycled paper, and is a loose fill that must be installed professionally. It can only be used in roof and ceiling spaces, and is a good option if your roof space is difficult to access.

Cellulose fibre can be dusty, so you need to put in barriers to prevent it falling down through exhaust fans, vents and the like. Some manufacturers spray it in with a sealer. Cellulose fibre is treated with borax and boric acid to make it fire and insect-proof.

The other issue with cellulose fibre is settling. According to the Australian standard, the R-value any insulation product claims should be the one it achieves in the long term, so a reputable installer will quote the R-value of the product when it has settled. (See Don’t get ripped off)

Boards (extruded polystyrene or expanded polystyrene)

Extruded polystyrene keeps the air in and water out, while expanded polystyrene isn’t water-resistant. Boards are useful especially if space is limited. They have to be installed between non-combustible surfaces, such as plasterboard, reflective foil or brickwork.

Polyester

Polyester fibres (including recycled PET bottles, such as soft-drink bottles) can also be made into batts and blankets. Polyester is a good choice if you’re insulating a space you’ll go into occasionally, such as an attic, as it doesn’t create extra dust or have loose fibres. It also doesn’t cause any irritation during installation.

Reflective foils

Reflective foil insulationFoil can cut out 95% of radiant heat, so it’s a particularly good material for keeping a house cool in summer or in a climate that’s hot much of the year. Reflective foil can be installed under the floor, in the roof construction or the walls of a house.

It’s possible to install silver batts yourself, but keep in mind there needs to be a still air space of at least 25 mm below the foil in order for it to be effective. Foil sarking also provides a condensation barrier and can act as a ‘second skin’ under tiles, protecting ceilings and walls from leaks and cracks.

Make sure there are no tears in foils — they decrease its performance as a vapour barrier. Surface dust can also decrease the foil’s R-value, which is why it must always be installed with the reflective surface facing downwards. See Table 1 for where the different insulation products would typically be used.

Table 1: Where to use different insulation products

Suggested applications for insulation products
Insulating material Flat ceilings /
pitched roofs
Cathedral or
raked ceilings
Timber
floors
Suspended
concrete slabs
Concrete
slab edges
Full
masonry walls
Framed walls
Glasswool batts or blankets
Rockwool batts or blankets
Glasswool / rockwool — foil attached
Natural wool batts or blankets
Polyester batts or blankets
Cellulose fibre
Granulated rockwool
Natural wool — loose fill
Reflective foil
Concertina foil batts
Multi-cell foil batts
Extruded polystyrene (styrofoam)
Expanded polystyrene (EPS)
Expanded polystyrene — foil attached

Judging from some subscribers' reports about installation, expect anything from a fantastic to a horrendous experience.

Here’s what to look for before you leap:

  • Be clear about what you’re trying to achieve. For example, the major cause of a hot home could be unshaded windows, so installing shading will be just as important as insulation.
  • Consider where you’re going to insulate — in existing homes, it’s usually the ceiling, but you can insulate under suspended timber floors.
  • Although some experts recommend wall insulation for existing homes, it’s difficult and relatively expensive and usually only occurs during construction or a major renovation. If you’re thinking of building, see Mandatory energy ratings for regulations governing the energy efficiency of new buildings.
  • Next, decide which insulation you’re going to use (see Insulation products, and Table 1). If you decide on loose fill, you’ll need to have the insulation professionally done; if you want to do it yourself you’ll have to choose batts (see DIY for more).
  • Check what R-value is recommended for the area you live in, and that you can get that value in the material you’re thinking of using. Ask about the price per square metre of the insulation you’ve chosen — this can vary, so be prepared to shop around.
  • Check your chosen product is accredited to the Australian and New Zealand Standard 4859.1. Ask the supplier to show you any test certificates or performance guarantees they have for the product, as well as the product’s fire and pest resistance. (The body that tests insulation is called BRANZ — Building Research Australia and New Zealand.)
  • Ensure water can’t get into the roof you’re insulating, as moisture damages some insulation materials’ performance. If it does get very wet, experts recommend you remove it and have new insulation put in.
  • One reader told us her laundry ceiling fell in due to the weight of water from a pipe leaking into the insulation. While uncommon, it does happen with some materials, so check your roof space occasionally for leaks, especially after a storm.
  • Have an electrician check your wiring to make sure it can be safely covered by insulation, or advise how to work around it.
  • Some parts of the building structure (such as ceiling joists or steel frames) may have a lower R-value than the material placed between them, so higher levels of insulation need to be added around those areas. Insulation strips can be inserted between the joist or frame and the roof lining to reduce thermal loss.

Tips for an energy-efficient home

  • Draughtproof Make sure doors and windows are properly sealed — you can buy draught excluders or window seals very cheaply.
  • Seal your chimney with a damper. Avoid installing downlights — besides using a lot of energy, they penetrate the ceiling and insulation, causing heat loss.
  • Shade Keep your home cool in hot weather by shading the windows that directly receive sun (north, east and west-facing windows). External awnings block more heat than internal blinds (because the heat’s already inside by then). You can also plant deciduous trees near the windows.
  • Ventilate Ceiling fans are much cheaper than air conditioning and have less impact environmentally, though they don’t cool the air, only move it about to produce a breeze.
  • If you have air con, try to use it only on really hot or humid days and have it zoned, so you can turn it off in the areas of the house you’re not using.

If you live in a dry area of the country evaporative coolers are effective (although unsuitable during water shortages).

For more information on energy efficiency, go to the Australian Greenhouse Office's 'Your Home' guide.

With all insulation, there should be no gaps except around hot objects such as downlighting and gas flues. Any such gaps are called heat bridges and decrease the overall efficiency of the insulation. Experts advise you to get into the roof yourself after your insulation has been installed and check the job has been done properly. The exception is when you've had loose fill installed that's higher than the ceiling joists.

Loose fill - settling

Loose fill can settle over time, so you need to ensure you get what you pay for.

  • Talk to your installer - if they claim it won't settle, ask for a written guarantee.
  • If they admit to a certain amount of settling you can ask for the installation of more material to compensate. For instance, if the R-value is achieved at a depth of 100 mm, they may install 110 mm. However, this may mean the material will cover the ceiling joists (the usual joist height is 100 mm) until it settles. This could make walking around the roof dangerous.
  • The other option is to ask for a top-up in, say, six to 12 months' time.

A job poorly done?

  • If you find that an insulation job has been poorly or incompletely done, you're not obliged to pay until problems have been rectified.
  • Go to your state's department of fair trading or building regulatory bodies if you're unhappy with the work done.

DIY

The most commonly self-installed materials are batts. You'll find installation instructions on the packaging or the manufacturer's literature.

When installing rockwool or glasswool batts these materials can cause itching and respiratory irritation, so you must wear: Insulation

  • Dustmask
  • Goggles
  • Gloves
  • Long-sleeved shirt
  • Closed shoes

In fact you should really wear protective clothing when installing any insulation to avoid respiratory irritation from dust in the roof space.

Mandatory energy ratings

From July 2006 the Australian Building Codes Board (ABCB), which oversees the building of new homes, updated its energy efficiency provisions. These require new buildings to have a minimum five-star energy rating, which means a new building must reach certain standards for environmental performance. The provisions have been accepted by the Australian Capital Territory, South Australia, Victoria and Western Australia.

This mandatory rating will be part of the Building Code of Australia (BCA) from 2006. The ABCB has divided Australia into eight different climate zones, and the level of insulation and other energy requirements will depend on which one your home is built in.

While the ABCB is made up of representatives for all states, some states may decide to use their own provisions. For example, Victoria has its own five-star requirements, and NSW has a system called BASIX (the Building Sustainability Index), an online assessment tool for checking the energy efficiency of new homes.

Houses undergoing major renovations may also be required to follow these regulations — check with your state’s energy department.

The R-value of a material describes its thermal resistance — how much the material inhibits the transfer of heat. The higher the R-value, the more effective the level of insulation.

With bulk materials, the thickness of the product is the key factor in determining its R-value (see Table 2).

The R-value you’ll need depends on your particular climate. See Table 3: Climate and R-values or ask your local council what the appropriate R-value for your area is.

How are they measured?

R-values can be measured depending on the direction of heat flow (upward or downward). They’re known as ‘up R-values’ (resistance to upward heat flow, also called winter R-values) and ‘down R-values’ (resistance to downward heat flow, also known as summer R-values).

Foil-insulated systems tend to have higher down R-values. In hot, humid climates where houses are naturally ventilated, high down values and lower up values are appropriate for roofs and ceilings.

Overstated claims

Since May 2005, the Building Code of Australia has required all insulation materials to comply with the Australian and New Zealand Standard 4859.1. This means they’ll need to be tested by an independent company in their retail form when they’ve been compressed for packing, rather than immediately after production.

System vs product R-values

There are two ways in which R-values are listed:

  • System R-value includes the insulation value of air spaces and building materials working in conjunction with the insulation material when it’s installed in the building according to the manufacturer’s specifications.
  • Product R-value is the R-value of the product on its own.

When comparing prices be sure to compare products with similar-type ratings. As single-sheet foils have no R-value as a material on their own, they’re measured and labelled according to their system R-value.

Table 2: Insulation thickness for some specific R-values

Thickness required to achieve
Material R = 2.5 (mm)* R = 3.5 (mm)*
Glasswool batt (low density) 130 180
Glasswool batt (medium density) 100 140
Polyester batt (low density) 160 220
Polyester batt (medium density) 110 160
Sheep’s wool batt (low density) 150 210
Sheep’s wool batt (medium density) 110 160
Sheep’s wool (loose-fill, low density) 170 230
Sheep’s wool (loose-fill, medium density) 110 160
Rockwool batt 90 130
Rockwool (loose-fill) 90 130
Cellulose fibre (loose-fill) 100 140

 

Table notes

Source: CSIRO, Building, Construction & Engineering (modified).
* Rounded to the nearest 10 mm

Table 3: Climate and R-values

Recommended R - values
Climate type and example locations Roof / ceiling Wall
Cool temperate and alpine
Melbourne 3.0 1.5
Mount Gambier, SA 3.0 1.5 – 2.0
Ballarat, Vic 3.5 1.5 – 2.0
Canberra 3.5 1.5 – 2.0
Hobart 3.5 1.5 – 2.0
Thredbo, NSW 4.0 1.5 – 2.0
Hot humid and hot dry
Cairns, Qld 0 – 3.5 (A) 0 – 1.5 (A)
Townsville, Qld 0–3.5 (A) 0 – 1.5 (A)
Broome, WA 0 – 4 (A) 0 – 2 (A)
Darwin 0 – 4 (A) 0 – 2 (A)
Marble Bar, WA 0 – 4 (A) 0 – 2 (A)
Mount Isa, Qld 0 – 4 (A) 0 – 2 (A)
Tennant Creek, NT 0 – 4 (A) 0 – 2 (A)
Temperate and warm humid
Brisbane 1.5 – 2.5 1.0
Perth 1.5 – 3.0 1.5
Sydney 1.5 – 3.0 1.5
Alice Springs, NT 1.5 – 4.0 1.5 – 2.0
Bourke, NSW 1.5 – 4.0 1.5 – 2.0
Adelaide 2.0 – 3.0 1.5

 

Table notes

(A) The zero figure isn’t intended to suggest that no insulation is required. It indicates that insulation to reduce heat loss may not be cost-effective and can even contribute to overheating in homes without adequate sun control. In these situations use insulation that prevents heat gain without unduly restricting heat loss (high down values, low up values).

Reproduced with kind permission from Your Home Technical Manual .

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