Energy Efficiency Performance Claims
The Claims of Super Performance Insulation Unmasked!
What appears to be very high thermal performance may be less impressive when the basis of the different dimensional systems is understood.
USA “Customary” units are similar to the old British “Imperial” values, whereas New Zealand now uses the Metric “SI” system of units.
Click here to jump down the page to the Comparison Table
“R” values as Metric units or as USA Customary units
The New Zealand Building Code requires buildings to insulate against heat loss (or gain) and it uses “R” (Thermal resistance) values to express the insulation value of building components such as roof, wall, floor and window insulation. Many imported products express their thermal properties in terms of “U” (Thermal conductance) values.
It is important to remember that “R” and “U” values can be expressed in metric units or in Customary or Imperial units – and there is a big difference between the systems.
To convert New Zealand metric unit “R” values to Customary unit “R” values simply multiply the New Zealand “R” value by 5.678
For example, an imported product from USA must have an “R” value of at least “R” 5.678 to be the equivalent of an “R” 1.0 New Zealand product.
“U” values as Metric, Customary, or Imperial
In New Zealand “U” values are not used as much as “R” values, and yet they have a direct relationship with each other, as one is simply the reciprocal of the other:
i.e.
to convert “U” to “R” – divide 1 by the “U” value
to convert “R” to “U” – divide 1 by the “R” value.
To convert New Zealand metric “U” values to USA Customary “U” values simply divide the New Zealand “R” value by 5.678
For example, an imported USA product must have a “U” value of at least “U” 0.18 to be the equivalent of a “U” 1.0 New Zealand product.
The New Zealand Building Code H1 Energy Efficiency – Third Edition includes a series of replacement tables (Tables 1, 2a, 2b, 3 & 4) replacing corresponding tables of required “R” values in NZS 4218 : 2004.
The following table shows the corresponding USA Customary “U” values required to match the required typical NZBC H1 replacement tables’ “R” values
|
NZ “R” m2.°C/W |
NZ “U” W/m2.°C |
USA “U” BTU/hr.ft2.°F |
|
0.26 |
3.85 |
0.68 |
|
0.31 |
3.23 |
0.57 |
|
0.34 |
2.94 |
0.52 |
|
0.8 |
1.25 |
0.22 |
|
1.0 |
1.00 |
0.18 |
|
1.2 |
0.83 |
0.15 |
|
1.3 |
0.77 |
0.14 |
|
1.5 |
0.67 |
0.12 |
|
1.9 |
0.53 |
0.093 |
|
2.0 |
0.50 |
0.088 |
|
2.6 |
0.385 |
0.068 |
|
2.9 |
0.345 |
0.061 |
|
3.3 |
0.303 |
0.053 |
|
3.5 |
0.286 |
0.050 |