Home Insulation Buying Guide

The government's home insulation bungle has demonstrated the importance of knowing what's what.
 
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07.R-value - what is it?

The R-value of a material describes its thermal resistance — how much the material inhibits the transfer of heat. The higher the R-value, the more effective the level of insulation.

With bulk materials, the thickness of the product is the key factor in determining its R-value (see Table 2).

The R-value you’ll need depends on your particular climate. See Table 3: Climate and R-values or ask your local council what the appropriate R-value for your area is.

How are they measured?

R-values can be measured depending on the direction of heat flow (upward or downward). They’re known as ‘up R-values’ (resistance to upward heat flow, also called winter R-values) and ‘down R-values’ (resistance to downward heat flow, also known as summer R-values).

Foil-insulated systems tend to have higher down R-values. In hot, humid climates where houses are naturally ventilated, high down values and lower up values are appropriate for roofs and ceilings.

Overstated claims

Since May 2005, the Building Code of Australia has required all insulation materials to comply with the Australian and New Zealand Standard 4859.1. This means they’ll need to be tested by an independent company in their retail form when they’ve been compressed for packing, rather than immediately after production.

System vs product R-values

There are two ways in which R-values are listed:

  • System R-value includes the insulation value of air spaces and building materials working in conjunction with the insulation material when it’s installed in the building according to the manufacturer’s specifications.
  • Product R-value is the R-value of the product on its own.

When comparing prices be sure to compare products with similar-type ratings. As single-sheet foils have no R-value as a material on their own, they’re measured and labelled according to their system R-value.

Table 2: Insulation thickness for some specific R-values

Thickness required to achieve
Material R = 2.5 (mm)* R = 3.5 (mm)*
Glasswool batt (low density) 130 180
Glasswool batt (medium density) 100 140
Polyester batt (low density) 160 220
Polyester batt (medium density) 110 160
Sheep’s wool batt (low density) 150 210
Sheep’s wool batt (medium density) 110 160
Sheep’s wool (loose-fill, low density) 170 230
Sheep’s wool (loose-fill, medium density) 110 160
Rockwool batt 90 130
Rockwool (loose-fill) 90 130
Cellulose fibre (loose-fill) 100 140

 

Table notes

Source: CSIRO, Building, Construction & Engineering (modified).
* Rounded to the nearest 10 mm

Table 3: Climate and R-values

Recommended R - values
Climate type and example locations Roof / ceiling Wall
Cool temperate and alpine
Melbourne 3.0 1.5
Mount Gambier, SA 3.0 1.5 – 2.0
Ballarat, Vic 3.5 1.5 – 2.0
Canberra 3.5 1.5 – 2.0
Hobart 3.5 1.5 – 2.0
Thredbo, NSW 4.0 1.5 – 2.0
Hot humid and hot dry
Cairns, Qld 0 – 3.5 (A) 0 – 1.5 (A)
Townsville, Qld 0–3.5 (A) 0 – 1.5 (A)
Broome, WA 0 – 4 (A) 0 – 2 (A)
Darwin 0 – 4 (A) 0 – 2 (A)
Marble Bar, WA 0 – 4 (A) 0 – 2 (A)
Mount Isa, Qld 0 – 4 (A) 0 – 2 (A)
Tennant Creek, NT 0 – 4 (A) 0 – 2 (A)
Temperate and warm humid
Brisbane 1.5 – 2.5 1.0
Perth 1.5 – 3.0 1.5
Sydney 1.5 – 3.0 1.5
Alice Springs, NT 1.5 – 4.0 1.5 – 2.0
Bourke, NSW 1.5 – 4.0 1.5 – 2.0
Adelaide 2.0 – 3.0 1.5

 

Table notes

(A) The zero figure isn’t intended to suggest that no insulation is required. It indicates that insulation to reduce heat loss may not be cost-effective and can even contribute to overheating in homes without adequate sun control. In these situations use insulation that prevents heat gain without unduly restricting heat loss (high down values, low up values).

Reproduced with kind permission from Your Home Technical Manual .

 

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