Instant expert

Instant expert: Insulation

Find out all you never knew about insulation; learn how different types of insulation work, and how to choose the most useful kind to improve comfort and energy efficiency in your home.


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What is insulation?
Insulation plays a crucial role in reducing energy consumption in buildings by keeping heat inside in winter and outside in summer. However, insulation is not as straightforward as it seems because there are two distinctly different kinds of insulation which do very different jobs. It is important to understand this in order to maximise the benefits from insulation.

What is bulk insulation?
Bulk insulation comes in the form of batts or loose-fill and is made from bulky materials like glasswool (a kind of fibreglass), rockwool (aka earthwool), cellulose (ground-up paper/cardboard), polyester, or even wool off the sheep’s back! The tiny pockets of air trapped within these materials make them resistant to the conduction of heat – that is, the heat that moves through ceiling, walls and floor when there is a difference in temperature between inside and outside a building.

Thicker insulation means more air pockets and thus greater effectiveness at slowing the conduction of heat in either direction, so bulk insulation will help you in both seasons, moreso the greater the temperature difference between inside and outside. This principle of small, static air pockets reducing conduction of heat applies in all contexts: it is the way clothing, insulating window coverings and double glazing works, and why bubblewrap is a good insulator.

The most common way to measure the effectiveness of bulk insulation is in R-values. R stands for 'resistance to heat flow', and a very rough rule of thumb is that 5 cm thickness of standard bulk insulation materials corresponds to about R1 insulation value, although this varies depending upon the insulation material used. When choosing insulation, refer to the R-value quoted on the packaging.

How much bulk insulation do I need?
In the cooler parts of Australia (central/southern NSW, ACT, Victoria, Tasmania), the temperature difference between inside and outside can be 20°C or more at night in winter. Therefore, it is a good idea to have at least R4 ceiling insulation (the more the better, although each added unit of insulation suffers diminishing returns so going above R6 is unnecessary in most places), and at least R2 in the walls, to increase comfort and energy efficiency. If building or renovating in a warm climate with a mild winter, it may be appropriate to install thinner bulk insulation, but make sure to install reflective insulation under the roof and in the walls.

What is reflective insulation?
Reflective insulation, also called sarking, sisilation or anti-con, comes in rolls or boards and looks like aluminium foil. It works by acting as a mirror to radiant heat – that is, heat in the form of electromagnetic waves, such as the heat in sunlight or the heat that builds up in bricks, tiles, concrete or metal that is exposed to sunlight for hours. Reflective insulation is best at reflecting radiant heat away from the building interior in summer, but will not help much in winter because most winter heat loss in cold climates occurs as either conduction (which is what bulk insulation is designed to reduce) or convection (air moving through gaps in the building envelope).

Reflective insulation products sometimes quote two R-value figures:
• 'up R-value' (aka winter R-value), resistance to heat leaving the building, and;
• 'down R-value' (aka summer R-value), resistance to heat entering the building.

Most reflective insulation products have low 'up' R-values and high 'down' R-values, which reinforces the point that they are designed to keep buildings cooler in summer, not warmer in winter. So, do not install reflective insulation thinking that it will help you significantly in a cold climate in winter because it is unlikely to do so.

What should I install if building from scratch?
If you are building from scratch in areas with a cold winter, it is an excellent idea to install high levels of insulation during construction: R5 bulk insulation above the ceiling, R2.5 bulk insulation in the walls (and under the floor if it is suspended). Also install reflective insulation under the roof and in the walls. This protects the ceiling and walls from loss of heat through conduction in winter, and gain of radiant heat in summer, which translates to greater comfort year-around, and less need for heating and cooling than an under-insulated or uninsulated building. This in turn will improve the comfort of the house and save you lots of money and energy over time from avoided heating and cooling.

If you are building in a warm climate, the way in which you use bulk insulation very much depends on the design of the house, but you should always install reflective insulation in the ceiling and walls.

What should I install if renovating?
If renovating an existing house in a cold climate do so to the standards stated above, and always install bulk insulation in the ceiling first (since that is where most houses lose the most heat) and see how the house feels. If it is still not comfortable, and/or your heating bills are still too high, insulate the walls next, and the floor last (if necessary). I would not retrofit reflective insulation under the roof of a house in a cold climate because, by bulk insulating the ceiling properly, you should not need it, and it is a difficult, costly and potentially dangerous job.

Although a more difficult job, retrofitting reflective insulation under the roof of an existing house in a warm climate makes sense, but employ professionals to do the job because that is how two electrocution deaths occurred under the Home Insulation Program.

Can I install insulation myself, or should I get a professional?
A common question surrounding insulation is whether or not you can insulate a house yourself. The answer is that you can install batts or reflective insulation products, but there are many dangers in doing so – for example the danger of electrocution, the danger of creating conditions that could lead to a house fire, the danger of remnant asbestos products, the danger of hyperthermia in hot conditions, and the danger of falling through your ceiling. I recommend paying properly insured and trained professionals from a well-established company to do the job. However, if you are going to do it yourself you should do the following at the very least:
• familiarise yourself with the Australian standards surrounding insulation,
• seek professional advice on how to deal with fittings in the ceiling such as recessed light fittings (avoid installing them in the first place!), hot flues and exhaust fans ,
• get an electrician in to do a wiring inspection to make sure that your wiring is treated appropriately to avoid fire and electrocution risk,
• turn off the electricity to the house before you begin,
• wear head-to-toe clothing, gloves, goggles and a mask (many bulk insulation products are physical irritants),
It is not worth cutting corners if the result could be injury or property damage.

Properly installed, appropriate insulation is safe, effective and absolutely crucial to comfort and energy efficiency in buildings, so I urge everyone who is building from scratch or living in an under-insulated dwelling to invest in insulation as soon as possible. Rather than heating the neighbourhood, retain the heat you pay for in your house by insulating it properly.

Renters, or those who want a quick-fix solution for this winter, might like to try these DIY insulation ideas that don't require a full retrofit:

Matthew Ruffin is the manager of Progressive Sustainability. He is a specialist educator and consultant in energy, environmental issues and triple bottom line sustainability. Matthew completed over 1,000 educative home energy audits under the ACT Government’s now defunct Home Energy Advice Team (HEAT) program, during which he taught households how they could be more comfortable in their homes while saving money and reducing their environmental impact. He also teaches Green Building principles to builders through the HIA’s Greensmart program, and began lecturing at the University of Canberra in 2013, running their Sustainable Communities course.