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Building and Environment 40 (2005) 353366
Performance characteristics and practical applications of common
building thermal insulation materials
Dr. Mohammad S. Al-Homoud
Architectural Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia
Received 29 January 2004; received in revised form 21 May 2004; accepted 31 May 2004
Abstract
Buildings are large consumers of energy in all countries. In regions with harsh climatic conditions, a substantial share of energy
goes to heat and cool buildings. This heating and air-conditioning load can be reduced through many means; notable among them is
the proper design and selection of building envelope and its components.
The proper use of thermal insulation in buildings does not only contribute in reducing the required air-conditioning system size
but also in reducing the annual energy cost. Additionally, it helps in extending the periods of thermal comfort without reliance on
mechanical air-conditioning especially during inter-seasons periods. The magnitude of energy savings as a result of using thermal
insulation vary according to the building type, the climatic conditions at which the building is located as well as the type of the
insulating material used. The question now in the minds of many building owners is no longer should insulation be used but rather
which type, how, and how much.
The objective of this paper is to present an overview of the basic principles of thermal insulation and to survey the most commonly
used building insulation materials, their performance characteristics and proper applications.
r 2004 Elsevier Ltd. All rights reserved.
Keywords: Buildings; Thermal insulation; Reflective insulation; Thermal mass; Vapor retarder; Moisture control
1. Introduction
As climate modifiers, buildings are usually designed to
shelter occupants and achieve thermal comfort in the
occupied space backed up by mechanical heating and
air-conditioning systems as necessary. Significant energy
savings could be realized in buildings if they are properly
designed and operated. As a least cost energy strategy,
conservation should be supported in the energy future.For every unit of energy saved by a given measure of
technology, resources will be saved, and the annual
operating costs associated with producing that unit of
energy will be reduced/eliminated. Therefore, building
designers can contribute to solving the energy problem if
proper early design decisions are made regarding the
selection and integration of building components.
Thermal insulation is a major contributor and obvious
practical and logical first step towards achieving energy
efficiency especially in envelope-load dominated build-
ings located in sites with harsh climatic conditions.
Space air-conditioning can have a big share of energy
used to operate buildings. In the average American
home, for example, space heating and cooling account
for 5070% of its energy use [1]. This percentage could
be higher in other parts of the world with more harshclimatic conditions and less energy efficient buildings.
The amount of energy required to cool/heat a building
depends on how well the envelope of that building is
treated thermally, especially in envelope-dominated
structures such as residences. The thermal performance
of building envelope is determined by the thermal
properties of the materials used in its construction
characterized by its ability to absorb or emit solar heat
in addition to the overall U-value of the corresponding
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doi:10.1016/j.buildenv.2004.05.013
E-mail address: [email protected] (M.S. Al-Homoud).
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component including insulation. The placement of
insulation material within the building component can
affect its performance under transient heat flow. The
best performance can be achieved by placing the
insulating material close to the point of entry of heat
flow. This means placement of insulation to the inside
for climatic regions where winter heating is dominantand to the outside where summer cooling is dominant.
However, for practicality it is common to use insulation
to the inside or between wall cavities.
Massing of the enclosing envelope is a parameter that
is mostly related to the thickness and type of the
construction material used and its ability to delay heat
transfer through the building structure over a period of
time. It is another important parameter in determining
thermal performance of the building and hence the
energy required to provide thermal comfort in the
occupied space.
Insulation materials can be made in different forms
including loose-fill form, blanket batt or roll form, rigid
form, foamed in place, or reflective form. The choice of
the proper insulation materials type and form depends
on the type of application as well as the desired
materials physical, thermal and other properties.
Because most thermal insulation materials exhibit heat
flows by a combination of modes (i.e., conduction,
radiation, and convection) resulting in property variation
with material thickness, or surface emittance, the premise
of a pure conduction mode is not valid, therefore, the
term apparent is implicit in the term thermal conductivity
of insulating materials [24]. Published thermal conduc-
tivity values and those reported by manufacturers arenormally evaluated at laboratory standard conditions of
temperature and humidity to allow comparative evalua-
tion of thermal performance.
Thermal insulation materials like other natural or
man-made materials exhibit temperature dependent
properties that vary with the nature of the material
and the influencing temperature range. The impact of
operating temperature on the thermal performance of
insulation materials has been the subject of many
studies. Results indicate that insulation materials subject
to high temperature have higher thermal conductivity
and therefore higher envelope cooling load with varyingdegrees depending on the type of insulation material [5].
In addition to the operating temperature, the material
moisture content is another major factor affecting the
thermal conductivity of insulation materials. The higher
the material moisture content, the higher the thermal
conductivity. In buildings, insulation materials used in
walls and roofs normally exhibit higher moisture
content when compared to test conditions. The ambient
air humidity and indoor conditions, as well as the
envelope system moisture characteristics, play an
important role in determining the moisture status of
the insulation material. When conditions are favorable,
condensation can occur within the insulation material.
Studies on the impact of moisture content on insulation
thermal performance concluded that the effectiveness of
insulating materials at higher moisture content is
reduced in proportion to the moisture content level.
Higher thermal conductivity is obtained due to in-
creased energy transfer by conduction and, undercertain conditions, by the evaporationcondensation
process, in which moisture moves from warm to cold
regions [5].
Insulating the building very well is not enough if it is
not airtight. Infiltration can have significant contribu-
tion to energy waste especially in residences with loose
construction. Insulation applied on cracks and small
openings can hide them without preventing air infiltra-
tion. Infiltration is dependent on the tightness of the
building construction, exterior shielding, temperature
differences, wind velocity, and building height. There-
fore, it is important to seal and caulk all cracks and
penetrations, such as electrical outlets and light switches
that could be a source of uncontrolled air leakage into
or out of the conditioned space. A tight, well-sealed
residence is more energy efficient and requires less
insulation to achieve thermal comfort.
Air retarders can also be used to minimize air
infiltration by preventing heated or air-conditioned
indoor air from escaping the building through its shell.
The air retarder should block air only, not moisture and,
therefore, should have high perm rating (5.0 or higher)
to allow the escape of moisture that might have
migrated into the building component [6].
To avoid problems associated with well insulated tightbuildings such as poor indoor air quality and moisture
accumulation, it is important to provide adequate
ventilation. Ventilation air helps avoid the build up of
stale air and air pollutants in the conditioned space and
prevents elevated moisture levels which can cause
moisture condensation on window surfaces as well as
concealed condensation within walls and roofs during
heating season.
2. Thermal insulation
2.1. What is thermal insulation?
Thermal insulation is a material or combination of
materials, that, when properly applied, retard the rate of
heat flow by conduction, convection, and radiation. It
retards heat flow into or out of a building due to its high
thermal resistance [3].
2.2. What is thermal conductivity?
Thermal conductivity is the time rate of steady state
heat flow (W) through a unit area of 1 m thick
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homogeneous material in a direction perpendicular to
isothermal planes, induced by a unit (1 K) temperature
difference across the sample [2]. Thermal conductivity,
k-value, is expressed in W/m-K (Btu/h-ft-F or Btu-in/hr-
ft2-F). It is a function of material mean temperature and
moisture content. Thermal conductivity is a measure of
the effectiveness of a material in conducting heat.Hence, knowledge of the thermal conductivity values
allows quantitative comparison to be made between the
effectiveness of different thermal insulation materials.
2.3. What is thermal resistance?
Thermal resistance is a measure of the resistance
(opposition) of heat flow as a result of suppressing
conduction, convection and radiation. It is a function of
material thermal conductivity, thickness and density.
Thermal resistance, R-value, is expressed in m2-K/W
(h-ft2-F/Btu).
2.4. What is thermal conductance?
Thermal conductance is the rate of heat flow (W)
through a unit surface area of a component with unit
(1 K) temperature difference between the surfaces of the
two sides of the component. It is the reciprocal of the
sum of the resistances of all layers composing that
component without the inside and outside air films
resistances. It is similar to thermal conductivity except it
refers to a particular thickness of material. Thermal
conductance, C-value, is expressed in W/m2-K
(Btu/h-ft2
-F).
2.5. What is thermal transmittance?
Thermal transmittance is the rate of heat flow through
a unit surface area of a component with unit (1 K)
temperature difference between the surfaces of the two
sides of the component. It is the reciprocal of the sum of
the resistances of all layers composing that component
plus the inside and outside air films resistances. It is
often called the Overall Heat Transfer Coefficient, U-
value, and is expressed in W/m2-K (Btu/h-ft2-F).
2.6. How does thermal insulation work?
Thermal insulating materials resist heat flow as a
result of the countless microscopic dead air-cells, which
suppress (by preventing air from moving) convective
heat transfer. It is the air entrapped within the
insulation, which provides the thermal resistance, not
the insulation material.
Creating small cells (closed cell structure) within
thermal insulation across which the temperature differ-
ence is not large also reduces radiation effects. It causes
radiation paths to be broken into small distances where
the long-wave infrared radiation is absorbed and/or
scattered by the insulation material (low-e materials can
also be used to minimize radiation effects). However,
conduction usually increases as the cell size decreases
(the density increases).
Typically, air-based insulation materials cannot ex-
ceed the R-value of still air. However, plastic foaminsulations (e.g., polystyrene and polyurethane) use
fluorocarbon gas (heavier than air) instead of air within
the insulation cells, which gives higher R-value.
Therefore, the interaction of the three modes of heat
transfer of convection, radiation, and conduction
determines the overall effectiveness of insulation and is
represented by what is called the apparent thermal
conductivity which indicates the lack of pure conduction
especially at high temperatures.
Both vapor passage and moisture absorption are
more critical in open cell structure insulation as
compared to closed cell structure. Vapor retarders are
commonly used to prevent moisture penetration into
low-temperature insulation. Vapor retarders are used to
the inside of insulation in cold climates and to the
outside of insulation in hot and humid climates
(allowing moisture escape from the other side). Vapor
retarders placement, however, is a challenge in mixed
climates.
2.7. What are the benefits of using thermal insulation?
There are many benefits for using thermal insulation
in buildings, which can be summarized as follows:
1. A matter of principle: Using thermal insulation in
buildings helps in reducing the reliance on mechan-
ical/electrical systems to operate buildings comforta-
bly and, therefore, conserves energy and the
associated natural resources. This matter of conser-
ving natural resources is a common principle in all
religions and human values.
2. Economic benefits: An energy cost is an operating
cost, and great energy savings can be achieved by
using thermal insulation with little capital expendi-
ture (only about 5% of the building construction
cost). This does not only reduce operating cost, butalso reduces HVAC equipment initial cost due to
reduced equipment size required.
3. Environmental benefits: The use of thermal insulation
not only saves energy operating cost, but also results
in environmental benefits as reliance upon mechan-
ical means with the associated emitted pollutants are
reduced.
4. Customer satisfaction and national good: Increased use
of thermal insulation in buildings will result in energy
savings which will lead to:
Making energy available to others.
Decreased customer costs.
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Fewer interruptions of energy services (better
service).
Reduction in the cost of installing new power
generating plants required in meeting increased
demands of electricity.
An extension of the life of finite energy resources.
Conservation of resources for future generations.5. Thermally comfortable buildings: The use of thermal
insulation in buildings does not only reduce the
reliance upon mechanical air-conditioning systems,
but also extends the periods of indoor thermal
comfort especially in between seasons.
6. Reduced noise levels: The use of thermal insulation
can reduce disturbing noise from neighboring spaces
or from outside. This will enhance the acoustical
comfort of insulated buildings.
7. Building structural integrity: High temperature
changes may cause undesirable thermal move-
ments, which could damage building structure and
contents. Keeping buildings with minimum tempera-
ture fluctuations helps in preserving the integrity of
building structures and contents. This can be
achieved through the use of proper thermal insula-
tion, which also helps in increasing the lifetime of
building structures.
8. Vapor condensation prevention: Proper design and
installation of thermal insulation helps in preventing
vapor condensation on building surfaces. However,
care must be given to avoid adverse effects of
damaging building structure, which can result from
improper insulation material installation and/or
poor design. Vapor barriers are usually used toprevent moisture penetration into low-temperature
insulation.
9. Fire protection: If the suitable insulation material is
selected and properly installed, it can help in
retarding heat and preventing flame immigration into
building in case of fire.
2.8. What are the available types of thermal insulation?
Many types of building thermal insulation are
available which fall under the following basic materialsand composites [3]:
Inorganic Materials
Fibrous materials such as glass, rock, and slag wool.
Cellular materials such as calcium silicate, bonded
perlite, vermiculite, and ceramic products.
Organic Materials
Fibrous materials such as cellulose, cotton, wood,
pulp, cane, or synthetic fibers.
Cellular materials such as cork, foamed rubber,
polystyrene, polyethylene, polyurethane, polyiso-
cyanurate and other polymers.
Metallic or metallized reflective membranes. These
must face an air-filled, gas-filled, or evacuated space to
be effective.
Accordingly, insulating materials are produced in
different forms as follows:
Mineral fiber blankets: batts and rolls (fiberglass androck wool).
Loose fill that can be blown-in (fiberglass, rock wool),poured-in, or mixed with concrete (cellulose, perlite,
vermiculite).
Rigid boards (polystyrene, polyurethane, polyisocya-nurate, and fiberglass).
Foamed or sprayed in-place (polyurethane andpolyisocyanurate).
Boards or blocks (perlite and vermiculite). Insulated concrete blocks. Insulated concrete form.
Reflective materials (aluminum foil, ceramic coatings).
Fig. 1 shows a graphical comparison of the thermal
resistances of 5 cm thickness for common building
insulation materials. Concrete block is not considered
as an insulating material. However, it was included in
the figure as a reference (no insulation case) for
comparison purposes only.
3. Reflective insulation
3.1. What is reflective insulation?
Most insulating materials work by creating miniature
air spaces. Reflective insulation, on the other hand,
uses larger air spaces faced with foil on one or both
sides. If one single reflective surface is used facing an
open space, it is called radiant barrier. The performance
of reflective insulation depends on a number of factors
[3,6]:
The radiation angle of incidence on the reflectivesurface. The best performance of reflective insulation
is achieved when radiation falls at a right angle of
incidence on the reflective surface (perpendicular tothe surface).
The temperature difference between the spaces onboth sides of the reflective material. The greater the
temperature difference, the greater the benefits of the
reflective insulation.
The emissivity of the material. The lower theemissivity (the higher the reflectance) the better.
The thickness of the air space facing the reflectivematerial. Air space must exist on at least one side of
the reflective insulation.
The orientation of the air space. The direction of heat flow.
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3.2. How does reflective insulation work?
Reflective insulation reduces heat transfer by radia-
tion. Materials react to radiant energy falling on them
through the following [3]:
Absorptance a: fraction of incident radiationabsorbed through the material.
Transmittance t: fraction of incident radiationtransmitted through the material.
Reflectance r: fraction of incident radiation reflected
by the material.
Therefore,
a t r 1
For opaque surfaces, t 0 and a r 1: For a black
surface t 0; r 0 and a 1: Reflective (polished)
surfaces are characterized by high reflectance and,
therefore, low emittance ; materials ability to diffuse
radiant energy a; for gray surfaces), which makes
them effective in reducing radiant heat transfer in
buildings especially in hot climates. The emittance is a
function of the material, and the condition and
temperature of its surface. The reflective insulationworks as follows [1,7,8]:
Heat from hot surfaces radiates in a straight line toother cooler surfaces surrounding them. The reflective
insulation (radiant barrier) reduces radiant heat
transfer from such hot surfaces (e.g., roof or wall)
to cooler spaces (e.g., attic or living space).
The reflective insulation must be both a poor emitter(p0:1 emittance) and a poor absorber (good reflector,
X0:9 reflectance) of thermal radiation.
The first layer of reflective insulation is the mosteffective (stops about 95% of radiant heat flow).
Additional layers of reflective insulation create addi-
tional air spaces that reduce convection heat flow.
Although radiation is independent of orientation, con-vective heat flow depends greatly on both the orientation
of the air space and the direction of heat flow.
The resistance of air spaces and reflective insulationvaries with their location in the structure and the time
of the year (direction of heat flow).
White color is also effective in minimizing heat transfer
into buildings in hot climates because it is not only a
poor absorber of energy but also a good emitter.
3.3. When and where to use reflective insulation?
Reflective insulation comes as rolled foil (usually
aluminum), reflective paint, reflective metal shingles, or
foil-faced plywood sheathing. It is most effective in hot
climates with predominant cooling requirements.
The best application of a radiation barrier is in hotclimates just under the roof to reduce radiant heat
gain from the sun. It is also beneficial in walls
receiving direct sun radiation such as west walls.
Reflective insulation is of minimum benefits insurfaces that are heavily shaded and/or well insulated. Reflective insulation is not economic in cold climates
with predominate heating requirements. It further
might have adverse effects where the roof (attic) is
kept cooler when the winter heat gain from the sun is
reduced due to the use of reflective insulation allowing
more heat loss from the heated space below it.
Therefore, it is more cost effective to use more
thermal insulation rather than using reflective insula-
tion in such climates [6].
The reflective foil can be installed to create two airspaces each facing a reflective insulator.
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0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4
Conc
rete
Bloc
kVerm
iculit
e
Polye
thylen
e-Bl
anke
t
Fibe
rGlas
s-Blan
ket
Poly
styren
e-Exp
ande
d
Fibe
rGlas
s-Rigi
dBoa
rd
Polyuret
hane
/Poly
isocy
anur
ate-F
oam
Ma
terial
R-Value (m2.K/W)
Fig. 1. Thermal resistance (per 5 cm thickness) of common building insulation materials (Concrete block is added in the figure as a reference for
comparison purposes).
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The reflective insulation should be placed to avoiddust accumulation (e.g., foil face down in the roof).
It is not recommended to install reflective insulationon the top of roof (attic floor) insulation where it
might act as a vapor barrier and trap moisture in the
insulation during cold weather.
The reflective foil conducts electricity; therefore, itshould not be installed in contact with bare electricalwiring.
In addition to the reflective performance character-istics of reflective materials, other characteristics such
as strength, flammability, availability, and cost should
be considered. Reflective foils come with different
treatments against tearing such as laminated woven
mesh or bubble-pack between two foil sheets.
3.4. How thick should the air space be?
The resistance of air space is a function of itsthickness. Thinner air spaces have less resistance due
to greater conduction. Thicker air spaces, on the other
hand, have less resistance due to heat transfer from
convection currents. Therefore, the optimum air space
thickness should be used $ 20mm [7].
4. Thermal mass
4.1. What is the insulating effect from thermal mass?
Massing of the building structure is influenced by the
seasonal and daily temperature variations, which
determine the need for thermal resistance and mass of
the building structure. Insulation is more critical in
climates with extreme seasonal variations and small
daily variations while thermal mass of the building
plays a more significant role in balancing the indoor
temperatures in hot-dry climates with large diurnal
ranges. However, in order to balance the thermal effects
of the outdoor temperatures on the indoor environment,
different exposures might require different time lag
values. Details can be summarized as follows [8]:
Thermal mass reduces heat gain in the structure bydelaying the entry of heat into the building (until the
sun has set).
Internal mass stores excess heat, whether from the sun
or from internal loads of the building, for release
during unoccupied and cooler periods.
Material thermal mass is characterized by its time lag
which is the length of time from when the outdoor
temperature reaches its peak until the indoor tem-
perature reaches its peak.
The time lag required for each wall orientation and
roof is different as each peak heat gain occurs at a
different time.
North has little need for time lag (small heat gain).
East morning load should not be delayed to the
afternoon. Use either:
Very long time lag 14 h: However, mass with
long time lag is expensive and not recommended on
the east; or
Very short time lag. No mass at all on the east or atleast no mass on the outside of the east insulation.
South mid-day heat can be delayed until sunset by
using mass with medium time lag ($ 8h).
West orientation can also suffice with 8 h time lag as
the number of hours between peak west sun and
sunset is very short.
The roof requires a very long time lag as it receives
sunlight most of the day. However, since it is both
expensive and not practical to place heavy mass on the
roof, additional insulation rather than mass is usually
recommended for roofs.
Mass time lag largely postpones heat gain. Colors, on
the other hand, significantly reduce heat gain.
Building thermal mass plays a more significant role in
dry climates with:
High daily summer temperatures.
Large diurnal (daily) ranges.
Insulation is more critical than thermal mass in humid
climates with:
High summer temperatures and humidity.
Small daily variations.
5. Moisture control
5.1. How does moisture migrate through building
structure?
Moisture transfers into the building structure from
many sources. If enough quantities of moisture accu-
mulates in the building envelope and cannot escape, it
becomes a good environment for mold, mildew, and
other moisture-related problems. Different materials
have different moisture storage capacity which is a
function of time, temperature, and material proper-
ties. If moisture penetrates into building thermalinsulation it will cause it physical damage and will
adversely impact its performance by increasing its
thermal conductivity.
Four conditions are necessary for moisture to
accumulate in a building component and pose a source
of problems. These include a moisture source, a
moisture route for travel, a driving force, and a material
susceptible to moisture damage. Moisture can ideally be
controlled if one of these conditions is eliminated. The
most practical approach to controlling moisture in
buildings is through careful design and material selec-
tion [9].
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There are different sources and transport mechanisms
of moisture into building assemblies including [1,9]:
Liquid water flow from rain and plumbing leaks. Raincan penetrate through leaks around doors, windows
and other cracks in the building envelope.
Water vapor convection from air infiltration throughopenings and cracks in the building envelope. This is
a major cause of interstitial condensation in the
building envelope.
Water vapor from internal sources such as people,cooking, shower, laundry, and indoor plants.
Water vapor diffusion from parts with highermoisture levels (higher vapor pressure) to other parts
with lower moisture levels. From warm places (warm
inside air in cold winter or hot humid outside air in
summer) to cold places as warm air usually contains
more moisture than cold air.
Liquid water movement due to capillarity from the
ground through porous materials in the basement,foundation, ground floor slab and walls.
Released moisture which was previously stored in thebuilding structure during slow air drying construction
process. This normally plays a role only in the first
few years after building construction.
In reality, multiple moisture sources and transport
mechanisms normally act together at one time. Every
moisture transport mechanism can cause moisture
problems and can help dry building materials and
alleviate such problems as well. Therefore, it is not
always the best approach to prevent moisture transport
mechanisms but rather to control moisture sources,
control moisture transport and accumulation mechan-
isms, and encourage moisture removal (drying) in a
building assembly [9].
5.2. What are the factors that impact moisture problems?
Many factors impact the seriousness of moisture
problems in buildings. These include:
Local climate at the building site. The difference between the indoor and outdoor climate.
The type and quality of construction. Differentmaterials will hold and transport moisture differently.For example, concrete will allow more moisture to
pass and be stored more than wood or aluminum.
The amount of moisture generated indoors. The ventilation process. The type and position of the insulation used. The use and location of vapor retarder.
5.3. How to control moisture problems in buildings?
In order to control moisture in buildings, it is
important to understand the climate at which the
building is designed, its thermal systems, and consider
the following:
Select proper building materials and constructionmethods.
Prevent rain water penetration into the buildingenvelope by proper roofing and caulking around all
penetrations and cracks.
Control infiltration by sealing all air leakage path-ways around the building envelope.
Use proper ventilation and dehumidification. How-ever, in humid climates make sure that the incoming
ventilation air is not a moisture source where it might
be more humid than the inside air.
Use and properly locate vapor retarder in the buildingenvelope when applicable.
6. Vapor retarders
6.1. What is a vapor retarder?
A vapor retarder is a special material (treated papers,
paints, plastic sheets, and metallic foils) that reduces the
passage of water vapor. A material permeability (or
perm) determines the extent to which water vapor can
pass through it. The lower the permeability, the better
the material is as vapor retarder. Materials can be
classified based on their permeability as follows [10]:
Vapor barriers which are very impermeable to watervapor (p1 perm). These include polyethylene films,
aluminum foils, oil-based paints, vinyl wall coverings,sheet metal, foil-faced insulation, glass, rubber
membranes.
Vapor retarders which are semi-vapor permeable towater vapor (1o10 perms) and include plywood, un-
faced expanded polystyrene, paper and bitumen
facing on fiberglass insulation, most latex-based
paints.
Breathable materials which are permeable to watervapor (X10 perms) such as unpainted gypsum board,
un-faced fiberglass insulation, cellulose insulation,
cement, and other similar building materials.
6.2. Why use a vapor retarder?
When there is high level of moisture in the air of a
living space it can cause a lot of problems. When such
moist air touches a cold surface with a temperature that
is below or equal to the dew point of that air,
condensation will start to occur on that surface which
could accumulate and create problems. If this moisture
penetrates to the wall or the ceiling it could create an
environment for mold and mildew growth resulting in
health problems and damaging building materials. If it
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gets into the insulation material, it will adversely impact
its performance.
Thermal insulation can help cure or complicate
moisture problems. The temperature inside an insula-
ted component is changed and the new temperature
profile can either prevent condensation or make a
surface inside that component colder during winter thanit would be if un-insulated. Therefore, water vapor
traveling through that component can condense and
cause problems.
6.3. Where to use a vapor retarder?
The type and location of the vapor retarder to be used
in a building depends greatly on the prevailing climatic
conditions and whether moisture is expected to move
more into or out of the building. For example:
In regions with prevailing cold climate, moisture tendsto diffuse through building envelope from warmerand more humid inside air to colder and drier outside
air. Therefore, vapor retarder should be placed
towards the inside warm surface of insulation. The
exterior surfaces should be permeable to allow drying
towards the outdoors.
In regions with prevailing hot and humid conditions,on the other hand, moisture is expected to diffuse
through the building envelope from outside warmer
and humid air to the colder and drier inside
conditioned air. Therefore, vapor retarder should
generally be placed towards the outside surface of
insulation. In mixed climates, where moisture is expected to moveboth into and out of the space without predominance
of either, it is better not to use vapor retarder at all
and allow water vapor by diffusion to flow through
the building envelope into and out of the space
without accumulation.
Rigid foam insulation boards do not require addedvapor retarder treatment when placed to the interior
of masonry walls.
7. Thermal insulation selection
7.1. What are the selection criteria for building thermal
insulation?
Many parameters should be considered when select-
ing thermal insulation, including durability, cost,
compressive strength, water vapor absorption and
transmission, fire resistance, ease of application, and
thermal conductivity. However, the thermal resistance
of insulation materials is the most important property
that is of interest when considering thermal performance
and energy conservation issues. The factors that impact
the choice of insulating materials can be summarized as
follows:
1. Thermal performance
Thermal resistance
High R-value insulation material (e.g., fiberglass,
rock wool, polystyrene, polyethylene, polyur-ethane, ...).
Material thickness vs. thermal resistance.
Material density vs. thermal resistance.
Operating temperature range vs. thermal resistance.
Thermal bridging
Continuity of thermal insulation around walls/
roof.
No/minimum framing.
Thermal storage
Thermal storage benefits from massive walls
(e.g., concrete, adobe).
Time lag capabilities.
2. Cost
Extra cost of insulation (cost per R-value).
Extra cost of quality materials and workmanship.
Impact on labor cost.
Impact on air-conditioning equipment size and
initial cost.
Impact on energy/operating cost.
3. Ease of construction
Impact on workmanship requirements.
Impact on ease/speed of construction.
Impact on ease of operation, maintenance andreplacement.
4. Building codes requirements (safety and health issues)
Fire resistance capabilities.
Health hazards (toxic or irritating fumes).
Structural stability (load bearing vs. non load
bearing, compressive strength).
Odor and skin/eye irritation.
5. Durability
R-value change over time (e.g., foams filled with
gases heavier than air, that diffuse over time).
Water and moisture effects (absorption and
permeability). Dimensional stability (thermal expansion and
contraction).
Settling over time.
Strength (compressive, flexural, and tensile).
Chemicals and other corroding agents.
Biological agents (dry rot and fungal growths).
6. Acoustical performance
Sound absorption.
Sound insulation.
7. Air tightness
Vapor/infiltration barrier.
Wall/roof construction quality.
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Sealed penetrations.
No cracks.
Good weather stripping.
8. Environmental impact
9. Availability
Thermal insulation material selection procedure issummarized in the selection chart of Fig. 2. Performance
characteristics of common building insulation materials
are shown in Table 1.
7.2. What is the optimum economic thickness of thermal
insulation?
The more insulation does not necessarily mean the
better. Optimum economic thickness of insulation can
be defined as the thickness of insulation for which the
cost of the added increment of insulation is just
balanced by increased energy savings over the life of
the project (principle of diminishing returns).
Thermal insulation does not always have the same
effectiveness for all types of buildings. Its effectiveness
and economic value can best be determined through life
cycle cost (LCC) analysis, as illustrated in Fig. 3, which
is a function of the following:
The building type, function, size, shape, and con-struction.
The building component to be insulated (wall, roof,etc.).
The local climatic conditions at the building site. The type of insulation used. The cost of insulation (material and installation
costs).
The type and efficiency of the air-conditioning systemused.
The type and cost of energy used (the value of energysaved).
Maintenance cost.
Some insulating materials might require higher
thickness to be installed to make up for expected
settling (e.g., blanket type of insulation) over timeand/or to get the rated thermal resistance under varying
operating temperatures.
8. Thermal insulation applications
8.1. What is the best location of insulation with respect to
thermal mass?
The location of thermal insulation with respect to
mass is not critical from thermal resistance point of
view. Any building component will have the same
overall thermal resistance for the same insulation type
and thickness regardless of its placement within the
assembly. However, there are other thermal and
practical considerations for insulation placement as
follows:
1. Insulation placement to the inside
Protected by mass against outside environment and
damage. However, the structure will be closer to
the outdoor temperature.
Expansion/contraction becomes more important.
More thermal bridges due to the unavoidable
crossings and penetrations. Therefore, all penetra-tions and joints must be tightly sealed.
Minimized potential heating benefits from the mass
of the building structure.
2. Insulation placement to the outside
Support for summer convective cooling and winter
passive solar heating.
Allows mass to store excess solar and internal
gains. However, less durability due to the exposure
to outside environmental and damage effects.
3. Insulation placement in the middle
Provides even distribution of the insulation in the
component.
ARTICLE IN PRESS
Determine the required application
(building type and location)
Determine insulation thickness
Prioritize your selection criteria(k-value, cost, f ire, acoustical, etc.)
Specify all related costs
(initial, operating, maintenance ,etc.)
Identify available insulation materials
Eliminate unsuitable materials
Perform economic evaluation among
potential systems
Select the most attractive system
Fig. 2. Thermal insulation selection procedure.
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Perlite (naturalglassy volcanicrock)
32176 0.060.04 Excellent Fair Excellent Good 7601 High Low High
Vermiculite(naturalmineral)
64130 0.0680.063 Excellent Good Excellent Good 13151 V. high Low High
Sprayed-in-Place
Cellulose (wastepaper)
2436 0.0540.046 V. good Poor V. good (addedadhesives)
Good 801 fire retardantchemical maycorrode metals
Low High
Foamed-in-Place
Polyurethane & Polyisocyanurate(closed cell foam)
4055 0.023 Poor Good Excellent Poor
Low High Organic(toxicsmoke, off-gassingfrom agingplastics)
Roofs, cavities,irregular andrough surfaces(experiencedhelp needed).Hard to controlquality andthickness onsite. Needs timeto dry beforeenclosing toavoid moistureproblems.
ReflectiveSystems
Aluminized thinsheets(Reflective foil,separated by
airspaces)b
Reduces onlyradiant heattransferc
Good Excellent Excellent Excellent High d
CeramicCoatings(acrylic paintfilled withceramic microspheres - brush,roller or spray)
1.25 Radiationcontrol
V. goo d Excel lent (seamlesswater proofing)
Excellent Excellent High High (Rustproofing)
Note :aThermal conductivity varies with material density and thickness as well as temperature and moisture content .bIf one single reflective surface is used facing an open space, it is called Radiant Barrier .cThe effectiveness of resistance to heat flow depends on spacing, airspace orientation and heat flow direction. Must have low emittance p0:1 and high dFoil must face air space with face down to prevent dust accumulation .
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Can achieve a trade-off between the benefits of the
above two arrangements.
8.2. What are the practical installation methods for
insulating buildings?
Insulation installation depends on the type of
structure, the type of insulating material used, and its
location in the structure. For walls, the insulation can be
placed to the inside, to the outside or in between
(sandwich wall). The advantages and disadvantages of
each location are as discussed above. For roofs, the
insulation can be placed on top of the slab, beneath it or
on top of a suspended ceiling. There are different
methods of using/fixing the insulating material with the
most common methods for concrete structures summar-
ized as follows [3,6,11]:
8.2.1. Walls, roofs, and floors
Double wall system with the insulating material placedin between. This method allows the insulation to be
evenly distributed and is common although it costs
more in constructing the double wall system. It can be
applied to newly constructed buildings; however, it is
neither practical nor economical for application in
existing structures.
Nails driven to the concrete surface by special gun.The nail should be of enough length to penetrate the
insulation (normally rigid foam) thickness and hold it
into the concrete surface. Washers are also used tohold metal lath to the insulation that allows plastering
over the insulation. For outside surface applications,
additional metal siding or stucco covering is used on
top of the metal lath to provide protection to the
insulation from weather conditions.
Furring (Z-channels, T-channel metal furring or woodfurring) that is usually applied at the joints of each
two insulation rigid boards. The furring can be nailed
or fastened into the concrete to hold the insulation in
place.
Adhesives to fix insulation rigid boards to the wallsurface (full adhesive bed is recommended). Cleanli-
ness of the surface and compatibility of the selected
adhesive with the insulation used must be insured.
Hangers to carry batt insulation on top of suspendedceilings. All ceiling surfaces and penetrations (e.g.,
light fixtures) should be tightly sealed to prevent air
infiltration.
Foamed-in-place polyurethane or polyisocyanurateinsulation which can take the shape of the structureits applied to. This is suitable for irregularly shaped
surfaces. However, it is hard to control thickness and
R-value of the foamed-in-place insulation.
Insulated concrete blocks cores filled with insulationpoured-in, blown-in or foamed-in, or using concrete
blocks with insulating material in the concrete mix.
Insulating concrete forms either cast-in-place or pre-cast concrete with a rigid insulation foam (polystyr-
ene, polyurethane, or polyisocyanurate) placed in the
core (sandwich panel), or on one or both sides of the
concrete panel and held by plastic or steel rods and
ties. This system offers better and uniform insulation,
more airtight envelope, and faster construction.
However, it costs more than other construction
systems.
Gypsum board finish (at least 1.3cm thick) should be
placed over interior surfaces of plastic foam insulation
(e.g., polystyrene and polyurethane) for fire safety.
Typical insulation installation methods for concrete
and masonry structures (walls, roofs and floors, and
slabs-on-grade) are illustrated in the following Figs. 46.
8.2.2. Cavities
The most economical and practical way of insulating
closed cavities in existing wall systems is with blown-in
insulation (e.g., fiberglass, rockwool, or cellulose)
applied with pneumatic equipment or with foamed-in-
place polyurethane insulation.
8.2.3. Slab-on-grade
For slab floors, the perimeter of the slab is more
critical than the floor and its insulation is important
for thermal comfort and energy conservation purposes
(especially in cold climates). The total heat loss is
nearly proportional to the perimeter length than to the
floor area [2]. Therefore, it is more practical to insulatethe edges of the slab rather than the whole slab
area. Insulation can be placed in two ways as follows
[3,6]:
Over the exterior of the slab/footing edge. Thisreduces heat loss through both the slab and the
foundation. However, the insulation needs to be
protected from insects and outside damage. Poly-
ethylene plastic (0.15 mm) is used as a moisture
retarder beneath the insulation. A well designed
drainage system under the slab is important to avoid
water accumulation and the associated problems.
ARTICLE IN PRESS
Cost
Total Cost(A+B)
Insulation Cost(A)
Insulation Thickness
Energy Cost(B)
Optimum
Level
Fig. 3. Economic thickness.
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Between the slab and the interior of the footing. Thisprotects insulation against insects and damage. The
insulation should be extended to about 0.6 m beneath
the slab to increase the path of heat loss to the
outside.
8.2.4. Foundation walls
It is important to keep basements dry in order to
avoid moisture intrusion and condensation problems
that could cause physical damage as well as health
problems. For new construction, in cold climates, it is
recommended to insulate the outside of the exterior
walls using rigid fiberglass insulation with a damp-
proofing coating under the insulation over the entire
foundation supported by good perimeter drainage
system and a waterproof paint on the room side of the
foundation wall. However, for existing buildings, it is
more cost effective to insulate to the inside of the
foundation [6].
9. Conclusions and recommendations
Building type has its role in determining the effec-
tiveness of envelope thermal insulation on the thermalperformance of buildings. The use of more thermal
insulation is more critical in the envelope-load domi-
nated buildings compared to those buildings with more
internal-load dominance. Although wall and roof
insulation are important, roof insulation is generally
more critical than walls as it is continuously exposed to
the direct summer solar radiation during daylight hours.
This paper presented an overview of the performance
characteristics and the main features of common
building thermal insulating materials and their applica-
tions into concrete building structures in a comprehen-
sive and practical way for the practicing engineer and/or
ARTICLE IN PRESS
Inside plaster
Thermal insulation
Metal lath
Outside plaster
Concrete block
Inside plaster
(gypsum board)
Metal lath
(support)
Thermal insulation
Concrete block
Outside plaster
Concrete block
Outside plaster
Thermal insulation
Metal lath
Inside plaster
Concrete block
(a)
(b)
(c)
Fig. 4. Wall insulation placement methods. (a) Insulation placement
inside mass, (b) Insulation placement outside mass, (c) Insulation
placement in the middle.
Inside Plaster
Concrete slab
Water proofing
Exterior layer
Thermal insulation
Air space
Thermal insulation
Suspended ceiling
Hangers
Lighting fixtureConcrete block wall
Concrete slab
Water proofing
Exterior layer
Air space
Reflective insulation(aluminum foil)
Suspended ceiling
Hangers
Lighting fixtureConcrete blockwall
Concrete slab
Water proofing
Exterior layer
(a)
(b)
(c)
Fig. 5. Roof insulation placement methods. (a) Concrete roof
insulation, (b) Thermal insulation of a suspended ceiling, (c) Reflective
insulation of a suspended ceiling.
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building owner. The recommendations can be summar-ized as follows:
1. Proper treatment of building envelopes can signifi-
cantly improve thermal performance especially for
envelope-load dominated buildings, such as resi-
dences. Therefore, the proper selection and treatment
of the building envelope components can significantly
improve its thermal performance.
2. Wall and roof insulation are recommended for
buildings in all climates for more thermally comfor-
table space and, therefore, less energy requirements.
Insulation helps in reducing conduction losses
through all components of the building envelope.However, roof insulation is generally more critical
than walls and should be given more attention.
3. Moisture penetration and condensation could cause a
lot of physical damage and health problems. It could
also deteriorate the performance of thermal insula-
tion over time. Therefore, it is important to control
moisture in buildings through adequate ventilation,
infiltration control and the proper use and location of
moister retarders in the building envelope.
4. Infiltration is the most difficult variable to measure
and its losses are the most difficult to control.
Additionally, due to frequent opening of doors andwindows in residences, infiltration rates are expected
to be generally higher than anticipated. Therefore,
careful treatment of cracks and leaks should be
implemented.
5. It is important to provide adequate ventilation in
order to insure proper indoor air quality and
moisture control, especially in well-insulated tight
buildings.
Acknowledgements
The author would like to acknowledge the support
and facilities provided by King Fahd University of
Petroleum & Minerals (KFUPM), which made this
research possible.
References
[1] The US Department of Energy. Insulation fact sheet with
addendum on moisture control, DOE/CE-0180, USA, 2002.
[2] ASTM Standard C 168-97. Terminology relating to thermal
insulating materials, 1997.
[3] American Society of Heating, Refrigerating, and Air Condition-ing Engineers (ASHRAE). Handbook of Fundamentals, Atlanta,
GA, USA, 2001 [Chapter 23].
[4] Peavy BA. A heat transfer note on temperature dependent
thermal conductivity. Journal of Thermal Insulation and Building
Envelopes 1996;20:7690.
[5] Budaiwi IM, Abdou AA, Al-Homoud MS. Variations of thermal
conductivity of insulation materials under different operating
temperatures: impact on envelope induced cooling load. Journal
of Architectural Engineering 2002;8(4):12532.
[6] http://www.eere.energy.gov/buildings/components/envelope/
insulation.cfm.
[7] Nisson JD, Dutt G. The super insulated home book. New York:
Wiley; 1985.
[8] Lechner N. Heating, cooling, lighting design methods for
architects, 2nd ed. New York: Wiley; 2001.[9] Straube JF. Moisture in buildings. ASHRAE Journal
2002;44(1):159.
[10] Lstiburek J. Moisture control for buildings. ASHRAE Journal
2002;44(2):3641.
[11] Masonry Council of Canada. Guide to energy efficiency in
masonry and concrete buildings, Ont., CA, 1982.
ARTICLE IN PRESS
Concrete wall
Slab-on-grade
Concrete foundation
Inside plaster
Thermal insulation
Water proofing
Slab-on-grade
Insulation is extended
about 0.6 m below theslab floor all around theexterior perimeter.Concrete foundation
Concrete wall
Inside plaster
(gypsum board)
Thermal insulation
Water proofing
(a)
(b)
Fig. 6. Concrete foundation/slab-on-grade insulation. (a) Concrete
foundation interior insulation, (b) Concrete foundation exterior
insulation.
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