Insulation acts as a barrier to heat flow and is essential to keep your home warm in winter and cool in summer. A well insulated and well designed home will provide year-round comfort, cutting cooling and heating bills by up to half. This, in turn, will reduce greenhouse gas emissions.

Climatic conditions will influence the appropriate level and type of insulation. Establish whether the insulation will be predominantly needed to keep heat out or in (or both). Insulation must cater for seasonal as well as daily variations in temperature, see ‘Insulation levels for your Climate’.

Illustration of typical heat gains and losses in a temperate climate - Click to enlarge
Typical heat gains and losses in a temperate climate.

Passive design techniques should be used in conjunction with insulation. For example, if insulation is installed but the house is not properly shaded, built up heat can be kept in by the insulation creating an ‘oven’ effect. Draught sealing is important, as draughts can account for up to 25 per cent of heat loss from a home in winter.
[See: 4.5 Passive Solar Heating; 4.6 Passive Cooling]

Insulation can assist with weatherproofing and eliminate moisture problems such as condensation. Some types of insulation also have soundproofing qualities.

The most economical time to install insulation is during construction. For information on retro-fitting insulation, see ‘Adding insulation to existing buildings’.

There is little insulating value in most common construction materials, but there are some exceptions where little or no additional insulation may be required. Suitable materials include aerated concrete blocks, hollow expanded polystyrene blocks, straw bales and rendered extruded polystyrene sheets. Check with your local building information centre for more details.

Choosing Insulation

Insulation products come in two main categories – bulk and reflective. These are sometimes combined into a composite material. There are many different products available, see ‘Insulation types and their applications’ for further information.

To compare the insulating ability of the products available look at their R-value, which measures resistance to heat flow. The higher the R-value the higher the level of insulation. Products with the same R-value will provide the same insulating performance if installed as specified.

Graph of insulation in Australian homes (2008)
Insulation in Australian homes (2008)

Source: Australian Bureau of Statistics, 2008.

Check the information supplied on the product, including the R-value, the price per square metre and whether it must be installed professionally or can be DIY – some types of insulation require the use of masks and protective clothing. Ensure that it suits your particular application and will fit within the space available. Ask if performance guarantees or test certificates are available.

Compare the environmental benefits of different products. Ask about recycled content and how easily the product can be recycled after use. For example, some brands of glasswool, polyester and cellulose fibre insulation contain significant amounts of recycled context. Contact the manufacturer or industry association to find out more.

The appropriate degree of insulation will depend on climate, building construction type, and whether auxiliary heating and/or cooling is to be used. Refer to the section headed ‘Insulation levels for your climate’.

The Building Code of Australia (BCA) sets out minimum requirements for the R-values of materials used in construction of buildings. For reference, please refer to BCA 2010 Volume Two Part 3.12. It is generally advisable to exceed these for greater comfort and energy savings.

The higher the R-value the better the thermal performance.

Material R-values are supplied with bulk insulation and refer to the insulating value of the product alone. The higher the R-value the better the thermal performance.

Total R-values are supplied with reflective insulation and depend on the product being installed as specified.

R-values can differ depending on the direction of heat flow through the product. The difference is generally marginal for bulk insulation but can be pronounced for reflective insulation.

Up and down R-values should be quoted when installing reflective insulation in roofs, ceilings and floors.

Insulation Types and their applications

Bulk insulation traps air in still layers

Bulk insulation traps air in still layers.

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 bulk insulation products come with one Material R-value for a given thickness.

Reflective insulation mainly resists radiant heat flow 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.

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 or RFL.

Dust settling on the reflective surface will greatly reduce performance. Face reflective surfaces downwards or keep them vertical. The antiglare surface of single sided foil sarking should always face upwards or outwards.

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. Ensure system values provided by the manufacturer relate to your particular installation situation.

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.

The properties and uses of some common insulation materials are shown in the table at the end of this sheet.

Illustration of reflective surface properties
Source: SEAV Insulation Guide

Map of Australia's Climate Zones

ZONE DESCRIPTION
1 High humid summer, warm winter
2 Warm humid summer, mild winter
3 Hot dry summer, warm winter
4 Hot dry summer, cool winter
5 Warm temperate
6 Mild temperate
7 Cool temperate
8 Alpine

Insulation Level for your climate

The following table gives recommended minimum insulation levels for a range of locations.

These are the minimum requirements of the building code. Some experts believe that additional insulation can further improve building performance.

The table does not distinguish between directional R-values for roofs and ceilings. The most important thing to remember is that in high humid climates where houses are naturally ventilated, high down values and lower up values are appropriate for roofs and ceilings.

CLIMATE TYPE AND EXAMPLE LOCATIONS MINIMUM INSULATION LEVELS
(Material or Total R-values)
  ROOF/CEILING* WALL
Cool Temperate and Alpine
Reducing heat loss is the main priority
Melbourne, VIC 4.1 2.8
Canberra, ACT 4.1 2.8
Hobart, TAS 4.1 2.8
Mt Gambier, SA 4.1 2.8
Ballarat, VIC 4.1 2.8
Thredbo, NSW 6.3 3.8
High humid and Hot Dry
Reducing heat gain is the critical priority
Darwin, NT 4.1 2.8
Cairns, QLD 4.1 2.8
Broome, WA 4.1 2.8
Marble Bar, WA 4.1 2.8
Mt Isa, QLD 4.1 2.8
Tennant Creek, NT 4.1 2.8
Townsville, QLD 4.1 2.8
Warm/Mild Temperate and Warm Humid
Reducing heat loss and heat gain are equally important
Brisbane, QLD 4.1 2.8
Perth, WA 4.1 2.8
Alice Springs, NT 4.1 2.8
Bourke, NSW 4.1 2.8
Sydney, NSW 4.1 2.8
Adelaide, SA 4.1 2.8
Katoomba, NSW 4.1 2.8

*Note: These minimum insulation levels will be higher if your roof has an upper surface absorptance value of more than 0.4

Source: BCA 2010 Volume Two

Where to Install Insulation

Roofs and ceilings work in conjunction when it comes to insulation.

Verandah roofs should be insulated in hot climates where outdoor living spaces are used extensively, to reduce radiant heat gain. Heat build up under verandahs not only affects the space below but can affect conditions inside the house.

Bulkheads (wall sections between ceilings of different heights) must be insulated to the ame level as the ceiling, as they are subjected to the same temperature extremes.

Save up to 45 per cent on heating and cooling energy with roof and ceiling insulation.

External walls should be insulated to reduce radiant, conducted and convected heat transfer. Wall insulation can be installed:

Depending on the particular situation, some forms of insulation can double as a vapour or moisture barrier.

Save up to an additional 20 per cent of heating and cooling energy with wall insulation.

Floors require insulation in cool climates and often in other climates.

Insulate the underside of suspended floors:

Insulate the edge of slabs on ground:

Insulate the underside of slabs on ground:

Enclosing sub-floor spaces in mixed climates may be sufficient to reduce heat loss.

Save up to 5 per cent on winter energy costs with appropriate floor insulation.

Adding Insulation to Existing Building

Insulation can be added to existing buildings with varying effectiveness and cost depending on the construction type and where the insulation is being placed.

Ceilings and suspended floors with easy access are relatively simple to insulate post-construction.

Insulation board can be laid beneath floor finishes if there is no under-floor access.

Walls and skillion roofs are the hardest to insulate post-construction, as the internal or external lining must be removed. A good time to insulate walls is during re-cladding or re-plastering. Specialised products are available to insulate existing walls. Check with your local building information centre. External insulation or (if local building regulations permit) cavity fill are often appropriate solutions for double brick walls.

Retrofits and Renovations

Adding (or ‘retrofitting’) insulation to existing buildings provides a major opportunity to increase comfort and reduce energy costs and greenhouse gas emissions. An ideal time for doing this is during renovations.

This section explains how to retrofit insulation to various construction types. Refer to the previous sections of this sheet to determine the appropriate type and level of insulation for your climate.

Walls

Most walls will benefit from added insulation, and it is possible to add insulation to most construction types used in Australia. Autoclaved aerated concrete (AAC) already has a reasonable degree of insulation built into the blocks themselves, and straw bale is an extremely highly insulated system.

Apart from these exceptions, added wall insulation is essential in all climates. If it is not already fitted, or if existing insulation levels are not high enough, there are ways of installing it as a retrofit.

Cavity Brick Walls

Cavity brick walls have high thermal mass, but without insulation are usually too cold in winter, and often too hot in summer if exposed to prolonged heat wave conditions. If the cavity is insulated, the internal thermal mass (ie. the internal brick skin) is protected from external temperature changes, and becomes highly effective at regulating temperatures within the home.

Insulate existing cavities by sealing the bottom of the cavity if it is open to the subfloor, and pumping in loose bulk material to a measured density. This has been common practice in the UK and Europe for many years, and is becoming available in Australia, usually in one of the following forms:

It is important that such materials are installed by reputable manufacturers whose products meet either the Australian, UK or European standards.

Brick veneer, reverse brick veneer and timber framed walls

Brick veneer walls have the brick skin on the outside, which is not the ideal location for thermal mass. The bricks heat up in summer and radiate heat late into the evening, while in winter they stay cold and absorb heat from the house. Insulation is essential to protect the occupants from external temperature extremes that are exacerbated by the external brick skin.

Reverse brick veneer is much more thermally efficient because the thermal mass is on the inside, however good insulation is still mportant to maintain thermal comfort.
[See: 4.9 Thermal Mass]

Timber framed walls are low mass construction, and rely entirely upon insulation to maintain thermal comfort.

The two cavity fill methods previously described (polystyrene balls or mineral fibres) can be used to insulate these wall types if the lining or cladding is not being removed. More material may be required, as it will fill up not only the cavity but the width of the wall frame (brick veneer and reverse brick veneer). Note that the effectiveness of existing relfective sarking is greatly diminished by replacing the airspace with fill material. For timber frame walls, insulation is pumped into the voids between studs and noggings, but this can be labour intensive.

The ideal option, if the scope of the renovation permits, is to remove the internal plasterboard linings or external cladding and fit insulation into the stud frame.

Either bulk or reflective insulation can be retro-fitted to existing wall frames by either cutting up a roll and fitting the pieces between each wall stud, or by using a factory prepared product like bulk batts, concertina foil batts or multi-cell foil batts, which are easy to install and expand or fold into place. Reflective foil-backed plasterboard is also a useful material.

There is usually sufficient depth in a wall frame to add more than one layer of reflective insulation, including the necessary air gap of 25mm between layers. When installing from the room side, the foil should not have an antiglare coating on it.

R 2.0 (70mm) or R 2.5 (90mm) bulk insulation can be fitted between studs. It is important to choose the correct thickness of insulation to suit the thickness of the cavity.

Bulk insulation can be fitted between studs in the conventional manner, and depending on the thickness of the studs and the selected R-value, may or may not fill the entire wall frame width. Do not compress bulk insulation.

When used in conjunction with a layer of wall wrap foil, ensure there is an air space of at least 25mm between the batt and the wall wrap foil.
[See: 4.8 Insulation Installation]

Other wall types

Single skin high mass walls such as concrete block, rammed earth or mud brick can have their thermal performance radically improved by installing insulation on the wall exterior. The simplest method is to use polystyrene board with an external render, or batts fixed between battens at around 600mm centres, covered with a waterproof cladding.
[See: 4.8 Insulation Installation; 4.9 Thermal Mass]

Ceilings and roofs

It is possible to add insulation to all roof types common in Australia, and even if some effort is required to lift roofing, the benefit is well worth it.

Ceiling fires have increased significantly with the more common use of downlights that penetrate the ceiling. Care must be taken to ensure that minimum clearances around downlights are maintained and that transformers are not underneath the insulation. Wherever possible avoid recessed light fittings as these are a major source of heat loss.

Tiled roofs without sarking can have it added easily if the roof is being re-tiled. If the tiles are to remain in place and access is available to the roofspace, double sided foil or foil batts can be added between the rafters or trusses, directly under the tile battens.

Metal roofs need a condensation barrier directly beneath them: a layer of reflective foil sarking is an effective membrane and barrier to radiant heat, thus doing two jobs at once. It is usually necessary to remove the roofing to install this, but most metal roofing can be removed and reinstalled easily, without damage.

Illustration of ceiling insulation

If sarking has been fitted it may still be necessary to fit extra layer/s of foil beneath it. A minimum air gap of 25mm should always be maintained between layers. If the roof is being painted to restore colour, select the lightest permissible colour (heat-reflective roof paints are also an option), and then match the remaining colour scheme to it.

Ceiling insulation is simple to fit if the roof space is accessible. If the house has a flat roof or raked ceilings, there will be no access into the space except by removing and reinstalling the roofing or the ceiling lining. If the ceiling is being replaced, it’s a simple job to install insulation from below. Reflective foil backed plasterboard is a useful material in this situation, but may not provide sufficient insulation if used on its own.
[See: 4.8 Insulation Installation]

Roof
Floor
Illustration of roof insulation Illustration of floor insulation
 

Exposed subfloor (Pole home).

Enclosed or ventilated subfloor
(brick, brick veneer, timber frame).

Floors

Floors do not always require insulation. Refer to the previous sections of this sheet to determine whether floor insulation is requiredfor your situation.

Raised timber floors should have subfloor access, with soil clearance of around 400mm below the lowest timbers. This provides sufficient access to install insulation. Foil or bulk insulation will work well, but in either case care must be taken to ensure it is well supported and will not sag or fall down in time. Vermin also need to be accounted for. Insulation board can be laid beneath floor finishes if there is no subfloor access.

Concrete slabs are either suspended or slab on ground. Suspended slabs can be insulated in a similar way to raised timber floors.

A suspended concrete slab with an in-slab heating or cooling system installed must be insulated around the vertical edge of its perimeter and underneath the slab with insulation having R-value of not less than 1.0.

A concrete slab-on-ground with an in-slab heating or cooling system must have insulation installed around the vertical edge of its perimeter. The insulation must achieve a minimum R value of 1.0 in zones 1 to 7 and a minimum R value of 2.0 in zone 8. The insulation must be water resistant and be continuous from the adjacent finished ground level to a depth of 300mm or for at least the full depth of the vertical edge of the concrete slab-on-ground.

To install slab-on-ground edge insulation you can excavate a shallow trench around the slab edge, but you should avoid excavating right down to the bottom of the slab, as destabilisation of the foundation may occur.

Install a 40mm closed cell polystyrene board and fibre cement cover board around the entire slab edge, up to the height of the wall cladding. Ensure the termite barrier remains intact. For more effective performance (if needed) an additional fin of closed cell polystyrene board can be laid horizontally from the slab edge underneath paving, extending about 1-1.5m.
[See: 4.8 Insulation Installation]

Air Leakage

Householders can improve the energy efficiency of most existing and new homes by weathersealing. Overseas standards and research recognise that the weather proofing or draught sealing of houses is the most effective method of achieving direct energy savings, whilst maintaining healthy indoor air quality. It is estimated that Australian buildings leak 2-4times as much air as Northern American or European buildings, suggesting a tremendous opportunity for energy savings in Australia.

In Australia, households produce around 20 per cent of our total annual greenhouse gas emissions, of which heating and air-conditioning account for around 38 per cent. Draughts can account for up to 25 per cent of heat loss from a home.

According to the Mobile Architecture and Built Environment Laboratory there are currently no scientific programs on air leakage performance for Australian residential construction and the challenge is to identify where weather sealing can be improved and to develop appropriat

Additional Reading

Contact your State / Territory government or local council for further information on insulation considerations for your climate. www.gov.au

Australian Bureau of Statistics (March 2008), Environmental Issues: Energy Use and Conservation (Catalogue no. 4602.0.55.001)

BEDP Environment Design Guide
GEN 12 Passive Solar Design.

Department of the Environment, Water, Heritage and the Arts (2008), Energy use in the Australian Residential Sector: 1986-2020 www.energyrating.gov.au/library/details2008-energy-use-aust-res-sector.html

Insulation Council of Australia and New Zealand (2007), Insulation Handbook Part 1: Thermal Performance Total R-value Calculation for Typical Buildings.

ReNew: technology for a sustainable future magazine, Insulation Buyers Guide, Issue 88
www.renew.org.au

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