Reflective insulation is made of thin sheets of highly reflective aluminium foil laminate, which reflects heat from its polished surfaces while

Absorbing and emitting only a small amount. It must work in conjunction with a still air layer for maximum effectiveness (see figure 7.6).

An R value supplied by reflective foil insulation is equivalent to the same R value provided by bulk insulation. Reflective foil R values are influenced by the characteristics of adjacent air spaces, such as their orientation, thickness and temperature differences.

Adequate performance can be achieved by combining reflective insulation with bulk insulation and/or using specialist foil products, provided they are carefully installed. Any gaps or tears will significantly reduce performance, as will dust build- up on surfaces. Four types of reflective insulation products are currently available. Reflective foil laminate oil laminated to paper with glass fibre reinforcement

applied in rolls typically used as roof sarking and wall insulation Double-sided foil is more effective than single- sided, provided that both sides face a still air space; it is also more water resistant Double-sided foil is typically produced with an anti-glare coating—this reduces the insulation’s

effectiveness by around 10%. Multi-cell reflective foil products wo, three or four layers of laminated foil separated by partitioning to provide a one, two or three-layered cell structure Can be installed over ceiling joists and between or across wall studs, depending on the product

should be butted firmly together to prevent air movement through gaps value depends on the number of cells and the

Presence of still air layers between the batts and other materials Expandable concertina-style foil >

Double-sided reflective foil formed into an expandable concertina sed mainly under timber floors and between

wall studs adjustable width to suit varying gaps should be installed with an adjacent sealed air space and be well sealed against the building

frame Foil bonded to bulk insulation Reflective foil bonded to batts, blankets or polystyrene boards increases insulation benefits if installed with the foil facing a still air space blankets are a common method of insulating cathedral ceilings and under flat roofs.

The Building Code of Australia (BCA) is Volumes One and Two of the National Construction Code (NCC). The BCA is produced and maintained by the Australian Building Codes Board (ABCB) on behalf of the Australian Government and State and Territory Governments. The BCA has been given the status of building regulations by all States and Territories.
Australia’s broad range of climatic conditions have been grouped into eight zones, for simplicity. The main characteristics affecting envelope design for human comfort have been listed for each zone along with key responses.

Choose the climate zone for your site from the map and refer to the appropriate section for an overview of the climate and how to respond to it in passive design terms.

The BCA defines eight climate zones for thermal design within Australia. The designer or builder should be aware that the design and construction requirements of single dwellings differ for each climate zone.

There are many definitions of Australian climate zones. The zones used in this guide are defined by the Building Code of Australia.

Use this overview, and the highlighted references to other fact sheets to access more detailed information as you proceed through the various stages of designing, purchasing or altering your home.


The overall R value is the total resistance of a building element. It takes into account resistance provided by construction materials used in a wall

or ceiling, internal air spaces, thermal bridging, insulation materials and air films adjacent to solid materials. Each of these components has its own inherent R value, the sum of which provides the overall R value. Added R value the added R value or added thermal resistance is

the value of the insulating material alone. This is the term most used when buying insulation. The manufacturer should provide the R value of

bulk insulation. Some products will trap air or gas more effectively, and so will have a higher R value for a specified thickness. For example, 45 mm thick extruded polystyrene and 80 mm thick glasswool both have an R value of approximately 1.5. Reflective insulation must work in conjunction with enclosed air spaces between surfaces, and cannot be said to have an R value by itself. To compare the performance of bulk and reflective insulation, the resistance of any existing air space(s) must be calculated. Reputable manufacturers can supply this information. Note that the effectiveness of reflective insulation installed on horizontal or sloping surfaces will eventually be reduced due to dust build-up, which reduces reflectivity.

Thermal bridging is the transfer of heat across building elements, which have less thermal resistance than the added insulation. This decreases the overall R value (see figure 7.8).

Wall frames and ceiling joists are examples of thermal bridges, having a lower R value than the insulating material placed between them. Because of this, the overall R value of a typical ceiling is reduced. For example, adding R2.5 bulk insulation between timber joists will result in an overall R value for the whole ceiling of R2.2. Metal framing, which has lower thermal resistance, reduces the overall R value even further. Consequently, higher levels of added insulation must be installed to compensate for this. Figure 7.8: Thermal bridging through ceiling joists


7.9: Heat transfer through R1.7 insulated brick veneer wall

A national framework has been developed for House Energy Ratings which will address insulation as one of several components.

In March 1991, government regulations were introduced specifying minimum insulation levels for all new homes.

Buildings requiring a building permit may also have to comply with the regulations, depending on the local council.

The regulations ensure that a reasonable level of thermal insulation is incorporated into residential buildings. New buildings of classes I, II and III (includes all residential dwellings such as homes, flats and units, and the residential sections of hotels, motels, schools, special accommodation and health-care buildings) must reach these prescribed insulation requirements. The regulatory requirements may be met by: complying with either of the following two basic options shown in table 7.2; or achieving a House Energy Rating of at least 3 stars and at least equivalent to that which would be achieved using option A or B (see table 7.2), as assessed by a registered building practitioner accredited in the use of the Sustainable Energy Authority’s First Rate house energy rating software Common building materials, such as brick, timber or tiles have little inherent insulation value. The R values of some typical forms of wall construction are shown in Table 7.3. The regulations require a minimum R value of 1.3 for walls. Only 200 mm aerated concrete meets the Victorian minimum insulation requirements by itself. Brick veneer and weatherboard walls have R values of 0.51 and 0.53 respectively, thus needing the addition of insulation to comply with the regulations.