Insulation is the first line of defence in improving a home’s energy efficiency, according to Dr Richard Aynsley, an expert in sustainable architecture, insulation and interior airflow, but orientation, floorplan, shading and ventilation need to be part of the equation when deciding what types of products to use and where to install them.

Hot climate issues

In hot zones, such as Brisbane, Darwin and Perth, reflective barriers such as aluminium foil insulations are highly effective at preventing radiant heat from entering buildings. These should be installed where the sun hits – generally in hot zone houses this is the roof.

In addition to radiant heat, managing convective and conductive heat is also important. Convective heat is the type that is carried by airflow, and can be reduced through an appropriate combination of building sealing and ventilation.

Conductive heat is the heat transferred by matter, such as a concrete patio that has been absorbing radiant heat and then transfers it to whomever stands on it.

Dr Aynsley says that orientation can assist with reducing heat impacts – for example, locating living areas in the northern part of a home, bedrooms in the east, where heat will not be felt until most people are ready to get up and start the day, and carports and garages on the west to act as a buffer zone for the home.

Shading of walls and glazing is also important to reduce summer heat. In cooler zones, where passive solar heating through glazing to the north is embedded in the Building Code of Australia Section J requirements, he says home owners need to ensure that any estimate of beneficial heat gain is not compromised by glazing being shaded during winter by a high adjacent fence or a close-by neighbouring home. Any shade trees to the north should also be deciduous.

Cool climate insulation issues

One of the critical issues for more temperate climates, Dr Ansley says, is considering condensation risks caused by insulation and building sealing.

Dr Aynsley was one of the contributors to the Master Builders Association and Australian Institute of Architects 2011 Building Codes Handbook Condensation in Buildings.

The handbook says a lowering of the temperature within wall and roof spaces can increase the risk of condensation, which has a range of risks including the growth of toxic moulds and damage to building materials such as rotting of studs, corrosion of metal fastenings or “leaky building syndrome”.

“Interstitial condensation can be far more damaging to the building than surface condensation. Interstitial condensation can go unnoticed and if the building fabric has not been designed to allow moisture to dry from within it can become trapped and compromise the durability of the building and the health of the occupants,” the handbook says.

Higher levels of insulation are actually creating cooler external surfaces in temperate areas, leading to condensation occurring within the wall cavity in some cases. In warm climates, where insulation and airconditioning create cooler internal surfaces relative to external ones, it can occur inside the dwelling.

Dr Aynsley says airconditioning in the tropics can be a major contributor to condensation occurring and can promote the growth of toxic moulds that pose genuine risks to human health.

Another issue identified in the handbook is that interstitial condensation can build up within fibre-based insulation, and that at even one per cent moisture content their effectiveness is reduced as water is a better conductor of heat than air pockets.

“The closed cell structure of some foam insulation materials such as extruded polystyrene, phenolic, polyisocyanurate (PIR) and polyurethane (PUR) insulation are less susceptible to moisture and water vapour ingress and so are less prone to loss of insulative performance. Open cell materials such as mineral wool and expanded polystyrene are more at risk of loss of thermal resistance,” the handbook says.

And the warmer the interior is, the more moisture the air can hold and the more likely “dew point”, the temperature at which water will condense out of air, will be reached.

Ande Bunbury

Melbourne-based architect and former project manager built environment for Sustainability Victoria Ande Bunbury told The Fifth Estate that dew point is something she assesses for every room in a building she designs, as the risk of it occurring is greater where the exterior temperature is very low and the interior kept warm.

To mitigate the risk of condensation, where her assessment shows dew point is likely to be reached within the homes normal climatic and internal heating and cooling parameters, she adjusts the design of elements such as battens or adds extra sarking [an aluminium foil backed building paper for insulation and weather proofing] to the walls.

In cooler climates like Victoria’s where energy use for heating needs management, she says bulk insulation is an effective choice.

“Insulation is about creating stationary air pockets,” she says.

Bunbury, who is focused on sustainable design, says she prefers to specify polyester batts for bulk insulation in walls and roofs as it is possible to obtain products that are manufactured from recycled plastic bottles, and the insulation is fully recyclable at end of life. They are also low-irritant and do not off-gas any volatile organic compounds or other toxins.

There have also been developments in polystyrene composite board products, she says. This is panellised clad polystyrene that can be used as a structural element. In addition to reducing materials through being a combination of finishes, insulation and structural material, they also save considerable time during the building process.

Bunbury says that insulation is not something to be considered on its own, and that thermal mass and orientation are also important, as is the use of stack ventilation principles.

Other elements that can contribute to thermal performance include double-skinned roofs, and Trombe walls, such as a dark-painted wall with window that absorbs heat during the day in winter, and radiates it back out at night.

Landscaping around the house can be used to pre-cool air before it enters the house, through putting water features or vegetation on the prevailing wind side of a dwelling.

The dual climate

Aluminium reflective foil firm Wren Industries’ director Tim Renouf told The Fifth Estate that in a dual climate, such as Canberra’s, where summers are high in radiant heat and winter temperatures plummet, a combination of reflective foil and bulk insulation in the roof is best.

The foil barrier not only prevents the majority of radiant heat during summer entering the home, it will also protect the bulk insulation from being damaged by the kinds of extreme high temperatures that commonly occur within Australian roof spaces.

The products

Aluminium foil insulation comprises a layer of pure aluminium about six microns thick laminated to either plastic or paper. It has been in use in Australia since the 1960s. It is excellent at blocking radiant heat from moving downwards into a home, but will not stop heat escaping from the interior via the roof in winter.

Bulk insulation works on the principle of trapping numerous tiny pockets of stationary air, just like a feather doona. Types of bulk insulation in the typical “batt’ form include fibreglass, rockwool, polyester, natural wool, and cellulose-based insulations. Batts work like a sponge to either absorb heat or cold.

Spray-in insulations – a number of firms are now providing a form of cellulose-based bulk insulation which is a loose-fill type, applied via a spray-in or pump-in process. These work in a similar manner to batts, however, there needs to be care taken to ensure appropriate physical barriers are put in place within roof cavities or walls to stop insulation from causing the overheating of light fixtures, exhaust fans or electrical cabling. The barriers need to be put in place around where each specific fixture is located. While the majority of these insulations seem to include fire-retardant chemicals, such as borax or boric acid, this does not prevent overheating setting a roof truss on fire.

Phase change materials – these use a material such as a wax to absorb heat. Basically, encapsulated particles such as micronised wax will absorb heat and melt when the temperature rises, and then release the heat and return to solid state when they cool. Charles Sturt University at Albury-Wodonga installed a form of this type of insulation in the floors of a new administration building in 2011.

Bunbury says there is another version on the market which uses match-box sized blocks of plant-derived material within a paper-based sheeting that is suitable for walls. She says they emulate thermal mass, making them a good insulation choice for lightweight construction. The limitation with them is that once they have melted, they can’t absorb any more heat.

David Goodfield, research associate and operations manager at Murdoch University’s Environmental Technology Centre, researched the effectiveness of phase change materials for a postgraduate thesis in 2008. He designed and constructed a prototype lightweight home and incorporated a plasterboard with incorporated phase change micronised wax.

He told The Fifth Estate that his project showed the importance of ventilation and night purging in removing the heat emitted from the materials during the cooler part of the night in summer.

Ventilation systems are also helpful in using the material as a means of distributing heat, with it first warmed by being installed in proximity to gas heating, and ventilation used to distribute the retained warmth once heating is turned off.

The big things you should consider before any insulation retrofit

As the Royal Commission into the Home Insulation Program found, existing homes in Australia are likely to have risks in the roof space. Before any insulation retrofit is carried out, an inspection of the roof space by a licensed electrician is essential to ensure the safety of installers and to reduce the risk of post-installation fires or electrocution.

New homes also should receive an independent inspection of in-roof electrical wiring to ensure the appropriate standards were met.

More important points from the RC:

  • Insulation installation should be undertaken in a manner that allows anyone entering the roof space in future to still see where the joists are, as most ceiling materials are not designed for walking on and the risk of falling through is very real unless someone walks on the joists.
  • Installation of insulation involves two risky work situations – working at heights, and working in enclosed spaces. Roof cavities can also become extremely hot, and are often devoid of any form of lighting or ventilation. Care needs to be taken to manage heat stress risks for installers, as well as managing the height and enclosed space risks.

See our story Insulation – the problems, the scapegoats and why the Building Code needs amending

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  1. This was such an extensive study that will definitely benefit a lot of people, especially those who are in the architecture and engineering field. This topic is way too important not only to the building’s design, insulation, strength, but also to the important electrical cabling done in every building. Thank you very much for sharing this information.

  2. I find the comment of Mr Ruz employed by one of the ICANZ member companies who has the largest capacity to manufacture foil in Australia appearing to favour bulk insulation.


    Does Mr Ruz believe that bulk insulations are the best insulations for all the climates of Australia?

    Mr D’Arcy gave the Home Insulation Program bureaucrats a “skint” warning about electrical issues, but according to Royal Commission transcripts AND his sworn written Statement nothing about non conforming wiring in contravention of the Wiring Rules AS/NZS 3000.

    Wonder why? Perhaps the HIP scheme would not have proceeded, into many homes with unprotected cabling in roof spaces as revealed by the Master Electricians Association CEO Malcolm Richards.

    Royal Commission transcripts reveal even the electrical industry in March 9, 2009 were silent regarding unprotected wiring, the bureaucrats even ignored a letter from Workplace Standards Tasmania, March 11, 2009 warning amongst other issues, about major electrical issues.

    Mr Ruz, you provided evidence during the Royal Commission Home Insulation Program dovetailing with Malcolm Richards from the Master Electrician Association (MEA) basically attempting to discredit foil and its unique properties.

    Mr Richards MEA, admitted liability for the electrical industry, and State Electrical Offices because of dramatic photographs provided by myself Graeme Doreian, to the Royal Commission HIP showing gross violations of the Wiring Rules.

    BELOW Quote from Royal Commission Report Home Insulation Program

    9.3.50 It does appear that the Wiring Rules are, or in the past have not been, strictly adhered to and that this was a contributor to the electrical safety risks associated with RFL insulation. Mr Richards, for example, said that compliance with the Wiring Rules has not been actively policed for many years.

    If Mr Ruz is so positive about his statement, I quote Mr Ruz “I also feel that while the insulation benefits of reflective insulation are real and worthwhile in hot climates, your article may be exaggerating their benefits to a degree.”

    My reply
    Your observations “your article may be exaggerating their benefits to a degree.”

    You are obviously referring to all foil products having issues. Is this in an attempt to promote the bulk fibreglass insulation industry represented by ICANZ?

    Where is there real time controlled testing of bulk insulation and foil insulation products separately in hot climates, as well as milder climates that are warming.

    I believe that ICANZ supported an independent thermal test facility.

    “ICANZ (Insulation Council of Australia & NZ) spokesperson Dennis Darcy.
    Senate Inquiry: Home Insulation Program 17 Feb 2010: Public Hearings and transcripts, pg 56, second paragraph”;db=COMMITTEES;id=committees%2Fcommsen%2F12816%2F0005;query=Id%3A%22committees%2Fcommsen%2F12816%2F0000%22

    “We do agree, however, that a proper, independent, building research facility is needed in future to investigate claims independently and to give some direction on where we go”

    I have just come back from Darwin, and seeing various residential buildings being built using milder climate building practices with almost no shading, because the developers want to maximise profits with smaller land sizes – which is a recipe for increased airconditioning running costs, especially where electricity have just risen by 10% in the NT.

    EVEN a section of a major NT Government public building has no foil installed under its roof or walls, it’s almost impossible to “bear” the heat in this section. I am in disbelief.

    Simply: What would you prefer to have to survive being lost in the desert?

    A thick woollen blanket? Is heavy, holds heat and makes the body hotter OR

    An emergency foil space blanket? Is lightweight, reflects up to 97% of solar radiation and moderates your body temperature AND does not store heat, cooling down instantly to the conditions it is exposed to.

    Having given electrical and thermal evidence on the stand under oath to the Royal Commission Home Insulation Program, and the Royal Commissioner referencing me thirteen times in his final report I believe from my research I am able to know what was the real cause for the deaths of those innocent workers.

    Basically, there has I believe been collusion by many parties involved in the actual Home Insulation Program and the Royal Commission to ignore the national and public interest in providing radiant barriers (foil products) to protect humans from increasing solar radiation that is warming our planet.

  3. Just to add to this article, as well as the “scapegoat” article, there are many other issues which need to be looked at.

    The NCC-BCA regulatory minimum Total R-values, as well as the Star ratings scale itself, is completely unvalidated and a fraud on the public, I believe.

    Firstly, as NatHERS-Accurate energy ratings haven risen from 3 Star up to 6 Star, so does the Total R-value needed for roofs/ceilings, walls and floors. This is in defiance of the Law of Diminishing Returns which dictates that thermal benefit rapidly diminishes beyond the initial amount of insulation installed, a concept explained by CSIRO in 1991 technical bulletins.

    Unjustified and unvalidated regulatory Total R-values forces energy raters to select high insulation product R-values, and the public are being deceived into believing that “more is better”, a well known marketing technique. This topic has never been openly and transparently discussed in the regulations, and never been validated by whole house testing. Why?

    Example: there will be no demonstrated “overall” winter heating benefit from increasing floor insulation from R2.0 to R3.5. Maybe in Finland, but not the temperate SE Australian winter climates. If people disagree then show me the real testing evidence, rather than saying “computer modeling”. As we all know, NatHERS is in disarray, and this is just one example.

    Secondly, there is no in-situ real time controlled insulation product testing which demonstrates proven thermal NET BENEFIT, the foundation stone concept of Standards Australia, and Standards are called up by the building energy efficiency regulations.

    Industry write the Standards, and government will not tell Standards what to do. The supposed NET BENEFIT mostly flows to Industry, not to the public. It is my contention that there is considerable NET DETERIMENT to the public occurring.

    The R-values of all insulation materials, both bulk and foil need to be fully validated by an independent testing regime instigated by government because Industry will not do it.

    Bulk insulation R-values are derived by laboratory “conductive heat” testing for 4 hours between two plates set at 33 & 13 degC, the average being 23degC printed on bulk insulation labeling. This is a reliable test procedure for winter heat flow out, but not adequate for Australian hot climatic conditions.

    RFL foil insulation R-values are “calculated” based on historic testing of RFL in the USA in the 1950s, and adapted for Australian use with limited local data. The USA methodology was independently validated in Australia by physical testing of RFL foil in walls, by CSIRO in 1983-85.

    I note that St.Regis-ACI undertook real time testing of foil in roof spaces during summertime 1968-69, proving the benefits of foil radiant barriers for housing as well as roof space airconditioning ductwork.

    On the point raised regarding “still air” being necessary against foil surfaces, this is valid for winter, but is debatable in my opinion for hot climates. Why does RFL work so well in summer under highly ventilated factory or residential roofs? It is because downward foil surfaces are perpetual powerful low emitters of radiation, regardless of air flow conditions.

    It has all been proven decades ago (St.Regis 1968 and CSIRO 1983), but no equivalent, controlled, real time, long period, high temperature testing has been performed on bulk insulations for Australian conditions. Why? And the Insulation Standard says that environmental factors encountered in building must be accounted for.

    A level playing field is needed so that consumers can be confident that they choose products with proven thermal performance and suitability for the climate. And the long running regime of well paid and well known consultants to government needs to stop. A new approach is needed.

    I gave written and oral evidence to both the 2014 Royal Commission and 2010 Senate Inquiry into the Home Insulation Program. The best solution I believe is for a sweeping program of change starting with Senate Inquiry Recommendation 6:

    “The government should establish a dedicated and industry-independent program to research insulation systems and help develop efficient insulation policy”.

    And expands with part of Recommendation 11:

    “proceed with necessary research and changes to standards required to provide clarity around the efficiency of different forms of insulation for different climates; and review industry standards and workplace practices to ensure high quality standards across all jurisdictions and rebuild public confidence in the sector”.

    The current federal government was extensively briefed from 2010 to 2014 about the entrenched failing in Star ratings and relevant standards, and commitments were given to myself and Graeme Doreian that it would be done, upon coming to government. This never eventuated. RFL foil was targeted, made the scapegoat I believe to protect the shortcomings of the electrical industry, leaving the public ignorant of all the issues.

    It would appear to me that vested interests have shut down any conversation about the powerful findings of the Senate Inquiry and the government refuses to intervene to address all issues.

    I have also participated on insulation Standards Committees and believe there are many changes needed to protect the public interest.

    Someone has to say enough is enough. Having campaigned for some 20 years, and of late with Graeme Doreian, to expose a raft of issues affecting building energy efficiency, we conclude that safety and insulation product performance must be addressed simultaneously, which is not happening perhaps because these issues have not been addressed by all previous governments since 1991, in spite of all warnings.

  4. I agree it’s a good article, however disagree that it exaggerates the benefits of reflective insulation. Often, a combination of both bulk and reflective insulation will give the home owner an optimum solution for thermal comfort.

  5. On the subject of night purging – this is a noble cause that in more than 11 years of inspecting homes, TAFEs, schools and commercial buildings I have never seen carried off successfully.

    Not so long a go I retrofitted an almost brand new community centre that had been designed with “night purge” technology. This comprised large permanently straight through ankle height wall vents around the building perimeter and four high volume permanently open roof mounted exhaust fans. These are from the ceiling of the centre through the roof decking. The idea being that staff switch the exhaust fans on at night and the next morning the building starts the day from a much lower temperature base.

    And this may even be so. However, in the mainly heating environment of Melbourne the amazing level of continuous and uncontrolled ventilation made it an uncomfortable and amazingly inefficient building. And this is the state of the art?

    I await products and implementations with more finesse.

  6. Good article. However, you mention BCA Section J requirements in relation to Australian homes. Please note that Section J applies to Class 2-9 buildings which does NOT include detached homes. I also feel that while the insulation benefits of reflective insulation are real and worthwhile in hot climates, your article may be exaggerating their benefits to a degree.