Select either the roof or the walls of this house
to quickly determine the R-Value most suitable for your home.
To find out more about R-Values, what they are
and why they are so important,
please read the information supplied below:
What are R-Values
The higher the R value, the greater the insulating effect.
Remember, it is not the thickness of the insulation product that counts. It is the R value. Some products will resist heat transfer more effectively and so will have a higher R rating for a given thickness.
In the interests of environmental conservation Standards Australia has recently published AS2627.1-1993, Thermal Insulation of Roof/Ceilings and Walls in Dwellings. This standard is the first in a series which gives guidance on improving the thermal performance of dwellings. It is believed AS2627.1-1993 will contribute significantly to Australia’s long-term objective of energy conservation and reducing carbon gases. The handbook Home Insulation in Australia (a joint publication by Standards Australia and FARIMA) is a reference guide to the new standard. Individual State maps are provided as a general guide to recommended insulation levels throughout Australia. More precise recommendations are tabulated in AS2627.1-1993.
Products which have the same R value will provide exactly the same insulating effect as one another, provided they are correctly installed.
Optimum R-Value
AS2627.1-1993 sets out the role of thermal insulation in achieving the design conditions of thermal comfort cost effectively. It nominates the optimum amount of thermal resistance (‘R value’) for some seven hundred and sixty (760) climate locations throughout Australia.
The amount of insulation required can be read directly from the tables of the 760 locations and can also be calculated for particular types of construction using the detailed method given. It aims at maximising energy savings while minimising costs to the home owner.
The optimisation method employed ensures that the present worth of estimated energy savings exceeds the estimated costs of supplying and installing the insulation. AS2627.1-1993 is uniquely and specifically Australian in that it deals with heating and cooling aspects with equal emphasis.
Typical Australian Dwelling
While good thermal performance of a building is achieved by a combination of measures, including thermal mass, orientation of the building, shading and double glazing, it is widely acknowledged that no other measure approaches the effectiveness of thermal insulation in the typical Australian dwelling.
AS2627.1 – Further Reading
AS2627.1-1993 is important reading for architects, builders, structural engineers and local government officers. It will also be of interest to individual homeowners.
Standards Australia has also published a suite of separate standards in the area of insulation materials for buildings. It is recommended that the official AS2627.1-1993 be purchased by those parties requiring regular reference to insulation standards.
Added R Value
The added R value is the value of the insulating material alone. This is the term most often used when buying insulation.
Overall R Value
The overall R Value is the total resistance of a building element such as a wall or ceiling. It takes into account resistance provided by construction materials, internal air spaces, insulation materials and air films adjacent to solid materials.
The overall R value is taken into consideration in Victoria’s Minimum Insulation Regulations.
Thermal Bridging
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.
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 construction element can be reduced. For example, adding R2.5 bulk insulation between ceiling joists will actually only achieve an overall R value for the ceiling of R2.2.
When thermal bridging occurs, the overall R value of a building element must be calculated using the following formula:
Roverall = 1/(A1/R1 + A2/R2)
Where:
A1 = proportion of the element’s area located between the framing components (eg. 0.9 not 90%)
A2 = proportion of the element’s area composed of framing (studs, noggings, top and bottom plates, joists, battens, etc.) (eg. 0.1 not 10%)
R1 = total resistance of area A1, found by adding together individual R values as above
R2 = total resistance of area A2
Australian Recommended R-Values
All insulation materials are rated for their performance in restricting heat transfer. This rating is expressed as the R-value , and is the measure of the material’s resistance to heat transfer (thermal resistance). It is a guide to its performance as an insulator: the higher the R value, the greater the insulating effect.
R Values are expressed using the metric units (m2.K/W), where:
- m2 refers to 1 square metre of the material (of a specified thickness);
- K refers to each "degree Kelvin" (or Celsius) temperature difference across the material;
- W refers to the amount of heat flowing across the material in watts.