Insulation Performance: R-value
The efficiency of any insulation material is measured by its R–Value or Thermal Resistance (R-2 or R2, for instance, means a thermal resistance of 2).
The greater the R-value of a product, the higher its insulating effectiveness. When dealing with contractors, always deal and think in R-values (not inches).
SI and non-SI Units
Some countries use the SI (International System of Units) units to express R-values, but many don’t. USA, UK and Canada don't use the SI units for thermal resistance, contrarily to countries like New Zealand or Australia...
Non SI units are expressed in a higher standard: the relation is approximately 1 (SI) to 5,67 (non SI).
Unless stated otherwise, we will use the non-SI values.
R-values depend on...
R-values vary with the insulating material: modern spray-on foams have far greater R-values per inch than traditional insulating materials like fiberglass, cellulose and mineral wool.
See, for details:
Spray-on foam insulation
Cellulose insulation
Fiberglass and Mineral Wool insulation
R-values may also depend also on...
- the number of layers of the insulating material to be installed
- density, in the case of loose-fill materials.
- the effectiveness of the installation.
A Proper Installation
An improperly installed insulation (e. g. a compressed batt insulation) doesn't provide the same R-value of a properly installed one. In the case of batts, compression and indentation may easily create air pockets which will reduce the insulation R-Value. That's just an example: things vary with the type of material and installation.
Extra-layers of insulation
Since the R-value per inch also depends on the thickness of the insulation material, installing an extra layer of insulation in your home will increase its R-value: the R-value of an installation with various layers of insulation is the sum of the R-values of the several layers of insulation.
Which R-value to apply
The R-value that should be applied in insulations depends on...
- particular climatic conditions
- particular parts of the house (ceilings, floor, walls...)
The demanded R-value may also depend (in a smaller scale) on the materials with which they interact: cement, tile, joists, studs... The insulation of a wall and the insulation of a ceiling may differ because the R-value also depends, in the last case, on factors as the heat that may flow through the joists and studs...
Un example
The table below shows some official recommended R-values for homes in the Pacific Northwest (a cold climate):
Ceilings: R-38
Walls: R-11
Basements, garages and other crawl spaces under floor: R-19
Crawl Space Perimeter: R-10 (exterior) and R-19 (interior)
Ducts: R-11
Pipes: R-3 or more in colder climates
For more details on demanded R-values for the different climate zones, see: Insulation and climate zones.
Up R-values and Down R-values
In roofs, ceilings and floors, when using reflective insulation materials, it is usual to consider two types of R-values: Up r-values and Down r-values.
Up R values or winter R-values define the resistance to heat flow upwards (heat escaping into outdoors through roofs or walls…).
Down R or summer R-values define the resistance to heat flow downwards (heat entering into the house through roofs or walls…).
An example: in a hot humid climate we should use insulation that prevents heat gains without restricting heat losses. Insulation should stop overheating. So, insulation materials should have a high Down r-value and a Low up r-value.
Examples of the R-Value of some insulating materials
| R-Values Per Inch of Some Typical Insulating Materials | |
| Mineral Wool Batts | 3.5 |
| Fiberglass Batts | 3.1-3.5 |
| Rock Wool (Loose Fill) | 3.0 - 3.3 |
| Cellulose (Loose Fill) | 3.2-3.8 |
| Fiberglass (Loose) | 2.2-2.7 |
| Perlite (Loose) | 2.3-2.7 |
| Polystyrene Boards (Rigid) | 3.6-5.3 |
| Polyurethane Boards (Rigid) | 5.6-7.7 |
See, for more details on Insulation Materials and their uses:
Insulation materials
Spray-on foam insulation
Fiberglass, mineral wool & Home insulation
See also:
Energy Efficient Windows for you county, state or country
Replace old windows by advanced energy efficient windows
Insulation benefits
Insulation performance
Roof Insulation
Home Attic Insulation
Walls Insulation
Ducts insulation
Floor Insulation
Slab Insulation
Pipe insulation
Moisture and insulation
How to deal with Insulation contractors and home builders
Insulation in your climate zone
Insulation tips
