Roof Insulation Specs

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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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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.

ARTICLE IN PRESS



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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 .


12/14

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.

http://www.eere.energy.gov/buildings/components/envelope/insulation.cfmhttp://www.eere.energy.gov/buildings/components/envelope/insulation.cfmhttp://www.eere.energy.gov/buildings/components/envelope/insulation.cfmhttp://www.eere.energy.gov/buildings/components/envelope/insulation.cfmhttp://www.eere.energy.gov/buildings/components/envelope/insulation.cfm

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