Insulation includes a variety of materials all utilised for their thermal resistance. These are typically installed in the ceiling/roof, floors or walls of a home, and act as a buffer against heat loss during winter, whilst slowing heat transfer from the walls or roof into living areas in summer. Roof and ceiling insulation can save up to 45% on heating and cooling energy, while an additional 20% can be saved with wall insulation. Choosing appropriate insulation is one of the most cost-effective ways of improving a home’s comfort and energy efficiency. Energy efficiency in the home is seen as a vital step in addressing environmental concerns regarding the impact of greenhouse gas emissions on the ozone layer. This has prompted government initiatives, in the form of grants to install insulation in homes. These are reflected in changes to the Building Code of Australia (BCA) which requires any new home in Australia to comply with improved energy efficiency measures and minimum insulation requirements for various climate zones within Australia.
The effectiveness of insulation is evaluated by its r-value which refers to the thermal resistance of the product, and often correlates to the thickness of the material according to Australian Standard AS/NZS 4859.1. R-values range from between 1 and 4, with a higher figure indicating a greater heat resistance, and therefore energy efficiency. The recommended R-value of a ceiling is usually double that of the walls.
Passive design techniques should also be used in conjunction with insulation. For example, if insulation is installed where the house is not properly shaded, built up heat can be kept in by the insulation creating an ‘oven’ effect. Similarly, draught sealing is important, as draughts can account for up to 25 per cent of heat loss from a home in winter.
Benefits of insulation
- reduces greenhouse gas emissions by reducing use of non-renewable energy resources
- save money on energy costs – heating/cooling systems operate more efficiently
- enhanced comfort – warm in winter, cool in summer
- improve fire safety – by eliminating air leakage in roofing
Types of insulation
There are two types of insulation i.e. bulk or reflective.
Reflective insulation is usually shiny aluminium foil laminated onto paper or plastic and is available as sheets (sarking), concertina-type batts and multi-cell batts. Together these products are known as reflective foil laminates. Dust settling on the reflective surface will greatly reduce performance. Reflective surfaces should be faced downwards or kept vertical. The antiglare surface of single sided foil sarking should always face up. The Total R-values for reflective insulation are supplied as up and down values. Total values depend on where and how the reflective insulation is installed. Reflective insulation mainly resists radiant heatflow due to its high reflectivity and low emissivity (ability to re-radiate heat). It relies on the presence of an air layer of at least 25mm next to the shiny surface. The thermal resistance of reflective insulation varies with the direction of heat flow through it.
Sarking is a layer of flexible insulation installed under roof tiles during construction. It consists of aluminum foil laminated onto paper or plastic backing with a flame retardant adhesive and fibreglass reinforcing mesh, and is manufactured in sheet form. As a thermal lining, sarking thermal lining is a very cost effective means of insulating a home. Roof sarking can contribute to the total R-value requirement for energy efficiency. Manufacturer’s specifications for the particular product will provide the R-value that can be included in the required ‘added’ R-value when a minimum 15mm air space is provided between the sarking and the roof cladding.
However, it must comply with the requirements of the Building Code of Australia (BCA), specifically relating to pliable building membranes (AS/NZS 4200.1.) and must not have a flammability index greater than 5. Its use can be mandatory or discretionary depending on a variety of local criteria including requirements for bushfire prone areas, wind speed and the specific construction specifications of your roof including length of rafter and tile profile. Australian Standard AS 2050 Installation of roof tiles requires sarking where the wind classification is greater than N3, and sets out the following requirements in relation to roof pitch and rafter length:
|Degrees of pitch||Max rafter length without sarking|
|18o to less than 20o||4500mm|
|20o to less than 22o||5500mm|
|22o or more||6000mm|
The Standard also requires sarking to be installed for a distance of 1800mm on either side of the point of discharge of downpipe or spreader carrying water from a higher roof to a lower roof.
Benefits of sarking
Foils are a versatile material for use in building applications, as they provide:
- high thermal reflectivity
- weather proofing
- dust reduction
- fire retardancy
Bulk insulation mainly resists the transfer of conducted and convected heat, relying on pockets of trapped air within its structure. Its thermal resistance is essentially the same regardless of the direction of heat flow through it. Bulk insulation includes materials such as glasswool, wool, cellulose fibre, polyester and polystyrene. All products come with one Material R-value for a given thickness. Should not be compressed or moistened.
Batts/blankets are strips or rolls of insulating material that are fitted to ceilings, roofs and walls and need to be tightly packed to maximise efficiency.
Glasswool/fiberglass is made from melted glass spun into a flexible mat of fine fibres.
Rockwool is made from volcanic rock melted at high temperatures and spun into a dense mat of fine fibres. It is an effective insulator but more expensive than glasswool.
Natural wool is made from sheep’s wool, and is an effective insulator though it needs to be treated for vermin and rot proofed.
Polyester is made from polyester fibres with similar properties as rockwool, and will not burn. This material is also a non-irritant with no known physical or health hazards.
Boards are typically made of polystyrene, sometimes with a foil surface suitable for ceilings, timber floors and masonry. These are an effective insulator, though expensive.
Loose fill is pumped, blown or placed by hand into an area, such as a roof ceiling. It consists of cellulose fibre, granulated rockwool or natural wool. It needs to be evenly distributed and not compressed to function efficiently.
Reflective products are made of aluminium foil laminated with glass fibre or foil paper, and need to be kept dust free to be efficient. Typically installed in ceilings, roofs or walls.
Soft foam insulation is a versatile application that is poured or sprayed. It adheres well to substrates and is suitable for walls, attics, ceilings and floors and carries no health risks.
Composite bulk and reflective materials are available that combine some features of both types. Examples include reflective foil faced blankets, foil backed batts and foil faced boards.
Electrical safety regulators across Australia have ongoing concerns about building fires caused by heat from recessed lighting setting fire to building material and other materials. Recessed downlights which operate at very high temperature are of particular interest.
If thermal insulation is installed too closely around these lights, or they are installed too close to combustible material such as leaf litter, it could cause a fire.
Transformers which supply the lighting can also suffer excessive temperature rise if covered by thermal insulation.
The Wiring Rules AS/NZS 3000:2007 have responded to this problem with specific new provisions on the precautions that must be taken for recessed luminaires including downlights. The Wiring Rules require that, unless a recessed luminaire is specially designed and certified by the manufacturer with specific installation instructions for use in close proximity to combustible materials, it must be installed with the default clearances and precautions detailed in the Wiring Rules.
Wiring Rules and downlights
The Wiring Rules AS/NZS 3000:2007 require that electrical contractors take special precautions where thermal insulation is of a type that is not fixed in position, e.g. loose fill. A barrier or guard constructed of fire resistant material is to be provided and secured in position to maintain the necessary clearance.
The fire resistant barrier or guard may be a commercially available device (including ones manufactured specifically for the light fitting used), or a barrier made of material that will prevent the down-light or transformer from transferring a dangerous level of heat to surrounding insulation, and which will itself withstand the heat of the down light or transformer.
Once a fire resistant barrier is selected, it should be installed around the light fitting (and transformer where relevant) in such a way that there is limited movement, allowing the required distance between the insulation and the light fitting to be maintained.
Default minimum clearances for recessed luminaires (Wiring Rules AS/NZS 3000:2007)
|Dimension||Incandescent lamp||Halogen lamp|
|Clearance – luminaire to building element above||50mm||200mm|
|Side clearance – luminaire to structural member||100mm||200mm|
|Clearance – luminaire to thermal insulation||50mm||200mm|
|Clearance – luminaire to supply transformer||50mm|
See Home Insulation.pdf for further information
Safety Issues stemming from Roof Insulation.
The installation of insulation products in the roof void of a domestic dwelling can create safety hazards. These hazards can be separated into two main types: hazards to occupants and hazards to tradespeople and others who enter the roof void.
Hazards To Occupants.
Electric Shock – Installation of insulation that conducts electricity such as metal foil that is interacts with electrical sources within the roof void and is also in contact with metal roof sheeting guttering and down pipes. This can occur as a result of poor installation of the insulation, poor electrical work, rats, possums and poor electrical maintenance.
Fire – Where insulation is poorly installed or is dislodged by following trades and as a consequence covers hot light fittings, the risk of fire is increased. Interaction of conductive insulation with poor electrical work can also be a source of fire.
Hazards to those entering the roof void.
Fall Hazards – It is essential for anyone entering a roof void to be able to check that the roof frame member that they will rely on to support their weight is in good condition and able to do so. Were insulation is installed wholly or partly covering these members a significant hazard exists end the roof void should not be entered.
Electric Shock – Installation of insulation that conducts electricity such as metal foil that is interacts with electrical sources within the roof void.
Toxic Dust – Roof Voids can contain dust and small particles that are a hazard to human health. the include mould spoors, pesticides, asbestos and fibre glass. Anyone entering a roof void should wear appropriate Personal Protection Equipment.
Heat Stroke – The air in roof voids can reach very high temperatures in summer and consciousness can be lost after only a short time. People should not enter roof voids where such conditions exist.