Source: Residential Efficiency Scorecard.

Insulation and the building shell, what are they and why are they important?

Your home may have efficient appliances, but still end up with a costly energy bill if the heat is coming in through an uninsulated ceiling or under doors. This is where the building shell is so important.

The building shell consists of the roof, walls and floor of your home, as well as windows and insulation. The materials used to build your home all have different properties. Some allow heat to move through them easily, others help retain heat. How well your home is sealed is another factor that determines how much it costs to heat and cool and how comfortable the house is to live in.

About your home’s building shell 

There are four parts to look at to improve the building shell. The improvement options on the certificate will highlight the weaker elements of your home.

  • Insulation, which acts to slow the rate of heat transfer through a material or building element, helping to keep the inside of your home warm in winter and cool in summer.
  • Thermal mass, which affects the rate your home heats up and cools down. Materials like concrete and brick have high thermal mass and help to slow down the rate that a room may heat up or cool down.
  • Windows, which have the combined function of letting in light and allowing heat movement in summer and winter.
  • Air leakage, which occurs through any gaps between the inside and outside of your home. These include deliberate openings like wall vents and chimneys, as well as gaps and cracks that develop over time.


Ceilings and roofs 
  • Between 25 and 35 per cent of heat loss or gain occurs through the ceiling. Adding ceiling insulation will make a huge difference to the comfort of the home, helping to keep it warm in winter and cool in summer.
  • If the ceiling space is easy to access, you can add or top up insulation so that you have a minimum of R3.5. If the ceiling space isn’t easy to access, consider adding insulation when the roof needs replacing or install an insulated false ceiling below the current one.
  • Between 15 and 25 per cent of heat loss and 25 to 35 per cent of heat gain occurs through walls. Walls can be difficult to insulate, so it’s best to do it while you are renovating and can replace lining or cladding .
  • Most stud walls have a 90 mm stud that allows insulation up to R2.5 to be installed. Alternatively, wall cladding is now available that can be retrofitted internally or externally that includes an insulated layer.
  • Between 10 and 20 per cent of heat loss or gain occurs through floors. Insulation is most effective on floors that have a large space underneath – and these are also often the most accessible. Raised floors are generally timber floors that can be insulated using batts or insulating boards affixed between the joists.
  • Slab on-ground concrete floors can’t be insulated after construction, so insulating the slab is only an option for new homes.
  • Installing insulation should be done in accordance with the Australian Standard (AS3999:2015) and the wiring rules (AS/NZS 3000:2007) to ensure it is done safely and will give the best possible results .
Thermal mass

Appropriately installed thermal mass inside your home can make it more comfortable. High thermal mass elements, such as brick, rammed earth, tile and concrete, tend to be slower to change temperature than low thermal mass elements. In winter, thermal mass exposed to the sun or your heater will mean your home remains comfortable for longer. In summer, thermal mass connected to the ground or other cooling sources will mean your home remains comfortable for longer. Thermal mass should be positioned so it is exposed to sun in winter but shaded from sun in summer.


Even the best performing windows will not insulate your home as well as an average  wall. This means that windows can be a major weak spot, letting heat out in winter and heat in during summer. Both the frame and the type of glass effect the performance of windows.

It is important to understand how to make your windows work to your benefit. While 10 to 20 per cent of heat is lost through windows in winter, the potential for heat gain in summer is much higher at between 25 and 35 per cent. There are many ways to manage windows to make your home more comfortable, including replacement or improvement.


Fixing gaps and cracks

For many homes the best way to improve comfort and save on your energy bills is to deal with gaps, cracks and other points that allow draughts. Between 5 and 25 per cent of heat loss or gain is due to gaps and cracks. Draughts also create airflow over your skin which make you feel colder in winter.

If your home has fixed ventilation, such as ceiling or wall vents, only remove it after seeking expert advice. Wet areas often need ventilation to avoid mould. You may need to install alternative ventilation such as exhaust fans.

Target these areas for sealing:

Exhaust fans

Exhaust fans should have louvres or flaps that close when not in use to reduce unwanted air leakage. If you can’t do this, try to keep doors closed to these rooms. You may even consider draught proofing internal doors if a room is a particular problem.


Chimneys for open fires can cause large amounts of air leakage. If you want to use your fireplace, you can fit a damper that blocks the chimney when it’s not in use.

You can block the chimney permanently if you don’t intend to use the fireplace. Often it is good to block the fireplace from the bottom or within the room. If the blockage is visible someone is less likely to try to use the fireplace in future.

Door and window seals

It is very common that windows and external doors are a source of draughts.  Signs are that windows rattle, dust accumulates around the inside of the frame or you feel cold air movement in winter.  If you can see light around a door this indicates a big problem.

There are many window and door seal products available that are suitable for different situations. If you’re looking for a less-permanent solution, you can stop gaps at the bottom of doors with a door snake.

Gaps can also occur around the outer edges of the frames where they meet the wall. These can be sealed with caulking and painted over.

Wall vents, ceiling vents and vented skylights

Homes built before the mid-1980s often incorporated wall or ceiling vents. You can seal or remove these vents unless you intend to use a portable un-flued gas heater or an open-flued gas heater in the room. Never use a portable gas heater in a sealed space.

Vented skylights incorporate a permanent opening, usually covered by fly screen or mesh. These are generally found in bathrooms and laundries. You can replace the skylight with a new type of sealed roof window or install a sheet of acrylic at the bottom of the shaft that blocks the entire hole .

A cheaper option is to close the door to the area with the venting. You may even consider draught proofing internal doors if it is a big problem.


Older style incandescent downlight fittings and gimballed (swivel) halogen fittings allow significant amounts of air leakage.

You can replace these with high-efficiency, sealed LED fittings that reduce air leakage, as well as energy use .

Floorboard gaps

Older floorboards may develop gaps between them and allow air leakage. Floorboards tend to shrink, expand and bend when walked on, causing fillers to fall out. This is a difficult issue to solve. The simplest approach might be to install carpet or rugs.

If the under-floor space allows it, you can insulate the floor from below with a product that provides an air seal like foil or insulating boards.

Skirting board gaps

Air leakage can occur in gaps between the skirting and the floor, especially in older homes. On a raised timber floor, there is likely to be significant leakage.

These gaps can be addressed by using a flexible caulking material, or you can use a foam noodle or filler on large gaps.



The most common forms of lighting found in homes are light-emitting diodes (LEDs), fluorescent globes and halogen globes. Incandescent (tungsten filament) globes were the most common form of lighting for decades but have been phased out over recent years to be replaced by more efficient types.

These can either be recessed into the ceiling (downlights), ceiling-mounted (pendant or track lights) or wall-mounted lights (sconces or track lights).

Light globes

Light Emitting Diode (LED)

LEDs are highly efficient globes with a very long life and come in many forms. LEDs can replace existing globes in general-purpose lighting fixtures (for example, bayonet or Edison screw) or downlight fittings.

LEDs also come in many colours of light. 'warm white' globes are similar to the colour of the older style incandescent globes. If you need more clarity for fine work or definition of objects, you may choose 'cool white' coloured globes.


Fluorescent globes are also very efficient and have only recently been surpassed by LEDs. Fluorescents can take the form of tubes, circles or more compact forms that can be used in general purpose fittings. Compact fluorescent lamps (CFLs) can be used as replacements in general-purpose lighting fixtures, although size constraints can limit the style and brightness of CFL you can use.


Incandescent globes are now rarely found in general fixtures, but are more common in specialised fixtures such as chandeliers or outdoor floodlights. Incandescent globes are inefficient, typically using 6 or more times the energy of an LED and can generally be replaced with LEDs or CFLs.


Halogen lamps are most often found in recessed downlights or track lighting, but there are also versions available to use in general light fixtures. Halogens typically use 6 or more times the energy of an LED and generate a large amount of heat.

Light fittings

Recessed light fittings

Most older style recessed downlights bring a few different issues to the energy efficiency performance of the house. If they contain halogen globes, they will be using a lot of energy and generating a lot of heat.

For this reason, insulation must be kept well clear of the part of the light fitting that protrudes into the roof. This means that the ceiling insulation in rooms with many recessed fittings is likely to perform poorly. Even small gaps in insulation can lead to a large drop off in efficiency. Gimballed downlight fittings (those that have an adjustable centre piece) and the larger style of recessed light common from the 1970s and 1980s often have significant gaps to allow heat from the lamp to escape. These gaps also allow air leakage from the room below in winter and from the roof cavity into the room in summer.

Track lighting

Older styles of track lighting (downlights) may still contain halogen globes which use a lot of energy. Track lighting does not have the same problems as recessed downlights in terms of gaps around the lamp or in insulation because they are attached to the underside of the ceiling.

Improving the performance of your lighting

Replace ceiling- and wall-mounted globes with LEDs. These are widely available through supermarkets, hardware and lighting stores. They will give you an instant reduction in energy consumption.

When replacing recessed fittings there are four options:

  1. Replace the globe in the existing fitting. Note that when replacing low-voltage halogen globes with LEDs, there may be incompatibilities between your existing transformer and the LEDs. This can lead to poor performance or flickering. This option will not solve the issue of gaps in insulation or air leakage through the fitting.
  2. Replace the transformer and the globes. This will not solve the issue of gaps in insulation or air leakage through the fitting.
  3. Replace the whole fitting with a sealed LED unit. New fittings have ratings that either allow insulation to be placed against the sides  or over the top of the fitting. Make sure you check the fittings insulation contact rating (IC).
  4. Replace recessed fittings with non-recessed fittings such as track lighting, pendant lighting, ceiling-mounted or wall-mounted lighting.

Consult your electrician for advice on the requirements for fittings and insulation.

Learn more about staying cool in summer and warm in winter, and consider these ideas when planning renovations and upgrades.

Other ways to save

Cut lighting power bills by:

  • Turning lights off in rooms when not in use
  • Using task lighting like reading lamps and turn off the main lights in the room
  • Ensuring low wattage sensor lamps are used if night lights are required for small children or in stairwells, rather than leaving a room light on
  • Choosing a lighter colours for ceilings and walls if re-painting as light coloured surfaces reflect more light
  • Placing new lighting circuits that allow you to choose which lights you have on in a room if you are renovating. The more flexibility you have to turn some lights off, the lower your energy costs will be
  • Checking to see if there are any government funded schemes that will change your light bulbs to more efficient ones

Hot Water Systems

There is a range of hot water systems now available in todays market.

Heat pump systems

Heat pumps are electric hot water systems that are more efficient than electric storage or instant systems. There are some very efficient heat pump systems on the market. Heat pump systems have a storage tank and use a similar principle to your refrigerator. Instead of pumping heat out of the fridge to keep it cool, they pump heat into the water. They use electricity far more efficiently than a traditional electric water heater.

Consider changing to a heat pump if you have solar power or intend to install solar power in the future. You can offset some the energy used by the heat pump with the solar system.

There is no star rating system for heat pump water heaters. Note that some heat pump hot water systems can be noisy to run.

Solar hot water systems

Solar hot water systems are an efficient way to heat water. Depending upon the time of year, most of your water can be heated free by energy from the sun.

Solar hot water systems use solar collectors, either flat panels or glass tubes, to heat the water. The hot water is then stored in a tank, which may be on the roof or on the ground.

Solar hot water systems will usually need boosting from another energy source on cloudy days and cold nights. Boosting can be from gas, electricity, or sometimes wood fuel. You can even retrofit a solar system to some existing hot water systems. There is no star rating system for solar water heaters.

Electric systems

Electric hot water storage systems can be very costly to run. Systems under 250 litres usually run on peak electricity rates which makes them expensive to run. This applies to many flats and smaller homes, these can be found under kitchen benches or in cupboards. Larger units over 250 litres often run on off-peak or controlled load electricity tarrifs and generally heat up overnight, which makes them cheaper to run.

Electric instantaneous systems are generally more efficient  than electric storage heaters, and modern models have better temperature control than older models. These units require dedicated wiring due to the high currents involved, so can be more costly to install.

If you have a solar power you may be able to offset some the energy that electric hot water systems use, making electric systems cheaper to run.

There is no star rating system for electric storage or instant water heaters.

Gas systems

Gas hot water systems can be a good option, especially if you have mains gas.

Instantaneous, or continuous flow, gas hot water systems heat only the water that you require as they don’t have a storage tank. Some models let you control the delivery temperature, and these can be different in different parts of the house, which provides safety advantages. These systems can be a good choice if you have variable hot water use as you will always have enough hot water. Instantaneous systems often require large gas pipes, which can increase the cost of installation.

Gas storage hot water heaters store hot water in a tank. Storage systems can be less efficient than instantaneous systems because of the energy lost through the walls of the tank. You may find you run out of hot water if the system is undersized or are heating too much water if it is oversized.

Gas hot water systems have a star rating. Try to choose a system with 5 or more stars if you are upgrading.
A list of current models with star ratings is available from the Australian Gas Association:

Wood fuel systems

Wood fuel systems are occasionally used to heat water, often as part of heating the home. These are more often found in rural areas where wood fuel is plentiful and mains gas is not available.

The performance of wood fuelled systems can be highly variable. The type and quality of fuel, the age and maintenance of the system all impact on efficiency. Wood fuel must also be cut and stored appropriately. It is very important to manage air quality impacts by operating the system efficiently as smoke can be unhealthy and inconvenient for you and your neighbours.