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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
|
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
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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R-Value
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