Insulation Performance: R-value
 

The Thermal resistance (R-value) of insulation materials

The efficiency of an insulation product 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 greater is its insulating performance. That's why, 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 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, obviously: modern plastica spray-on foams have far greater R-values than traditional insulating materials as fiberglass, cellulose and mineral wool.

See, for details:
Spray-on foam insulation
Cellulose insulation
Fiberglass and Mineral Wool insulation

Anyway, R-values depend also on...

- the thickness of the insulating material
- on density, in the case of loose-fill materials.
- the effectiveness of the installation


The effectiveness of an insulation

The performance of insulation depends on where and how it is installed.

The insulation of a wall and the insulation of a ceiling may differ because the R-value also depend on factors as the heat that may flow through the joists and studs...

Similarly, an improperly installed material (a compressed one, or an installation without adequate sealing) doesn't provide the same R-value of a properly installed material...


Extra-layers of insulation

Since the R-value 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 should be applied?

The R-value that should be applied in insulations depends on...

- particular climatic conditions
- particular parts of the house (ceilings, floor, walls...)

Besides these two major factors, the demanded R-value may also depend (in a smaller scale) on the materials with which they interact: cement, tile, joists, studs...
 
The table below shows some official recommend 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 - describe resistance to heat flow upwards (heat escaping into outdoors through roofs or walls…).

Down R – or summer R-values - describe 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

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
Pipe insulation
Moisture and insulation
How to deal with Insulation contractors and home builders
Insulation in your climate zone
Insulation tips

 

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