Journal Design + Built

The Role and Function of Thermal Insulation

The Role and Function of Thermal Insulation in Architecture

N. Nafici, M.F.M. Zain
Department of Architecture, Faculty of Engineering and Built Environment,
University Kebangsaan Malaysia
n.nazanin68@gmail.com

___________________________________________________________________________
ABSTRACT
With movement of cities toward a more industrial urban structure, they need of green
environment is increasing. One of the solutions is creating the green roofs which the interest on
them is increasing. However, having a green roof requires some technical guidelines to provide
the desired environment. The technical guidelines for instruction of green roof aim to provide
an adapted, environmental friendly and suitable material for offering the optimal operation. This
focus of this document is mainly on the technical aspects of the material in need for insulation,
roofing membranes and protection material, moisture-retention material and water proofing.
Keywords: Thermal Isolation, Green Roof, Landscape.
INTRODUCTION

Human beings always try to reach the optimal situation in their living places. After mid1970s which modern green roof movement started in Germany and fast spreading of it
through the world, environmental and energy benefits, structural material and its
design have been received more concerns and attention from academic researchers.
Nowadays, through the world and especially in Europe and North America the
residents try to have some features of green roof in their buildings.
Green roofs have many ecological advantages. They provide insulation and
cooling. They reduce urban heat in cities. The provided shade by them has a
significant cooling effect and decreases the temperature. Furthermore, the heat is not
maintaining in green roof the same as traditional roofs. On the other hand, they are
effective in sound insulation of the buildings which is an important point in urban areas
and enhance a wildlife habit. They improve the potential biodiversity in cites. Green
roofs also clean the air and save energy. They have a significant role in storm water
management, CSO control, and its impact on carbon dioxide reduction. Moreover they
are helpful in food production and aesthetic aspects.
The creation and maintenance of the green roofs need some especial facilities.
The green roof can be built on the varieties of the roof, but in the majorities of cases,
they are constructed on flat roofs. In addition to different kinds of roofs, they have also
different styles of building systems and used materials. In fact, always there is a
technique to construct green roof on any kinds of the roof. However the most common
problem is the limitation of the weight carriage capacities of the roof. The most
appropriate time for building a green roof is the time of a constructing a new building or
when the roof of an existing building needs fix or to be replaced, which in both
situation, a structural analyst should be hire for consultation, to determine the
appropriate procedure that the rood needs to support a green roof.
Despite that the cost of the constructing of a green roof is more expensive than a
conventional one, but its long-term benefits can be a simulating reason for the

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The Role and Function of Thermal Insulation

choosing the green roof. The costs of a green roof can be different depending on the
design, material, climate, and plants.
In order to utilize the positive points of green roofs, different issues should be
concerned such as transfer of energy, moisture, air and heat. Even so the issue of
water management has a critical role. However, besides of applying good strategies
and material geographical and environmental issues should receive enough attention.
In this article, we will investigate some of the materials and strategies which they have
been used in the structures of green roof.
ROOFING INSULATION

Green roofs are good roofing insulators that prevent heat flux through the roof (Barrio
1998)[1]. They consist of insulation materials that are boards placed over the roof
surface. These insulators are set below or above water proof and roofing materials. If it
is placed above, it needs to be made of material that is capable of exposing of a wet
condition. On the other hand sometimes we need a protective layer, since some
insulation layers cannot resist to high temperature. Polyiso-cyanates, extruder
polystyrene, expanded polystyrene and fresco boards are the most famous roof
insulator materials.
Polyiso-Cyanurate
It is also referred to as PIR, poly iso, or ISO, is essentially an improvement on
polyurethane (PUR). It is the main roofing insulator and typically is informed of foam
and used for rigid thermal insulation. It will install before roofing membrane. It should
be kept dry and its weight per inch of thickness is 0.2 to 0.3 lb/ft2, (Figure 1). There is
more detail in British standard BS 4841:2006.

Figure 1 : Polyisocyanurate rigid insulator

(Source: www.insulationireland.net)
Extruded Polystyrene

Polystyrene is a thermoplastic material, which is in a solid-state at room temperature,

but flows if heated. Polystyrene foams are used as building insulation materials
because they are good thermal insulators. Extruded polystyrene (PS) is economic
polystyrene. It can be installed bellow or above a membrane. It is very resistant to
absorbing water and its weight per inch of thickness: 0.25 lb/ft2, (Figure 2 ). BSI
standard number BS EN 14934 specifies the properties of this material.

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The Role and Function of Thermal Insulation

Figure. 2: Extruded polystyrene

(Source: www.homeconstructionimprovement.com)

Expanded Polystyrene
It is usually in white color with low density and low thermal conductivity, which is
another type of polystyrene that should be installed, bellows the roofing membrane. It
is introduced in BSI standard number BS 3837. It also used for packaging industry. It
should be kept dry and its weight per inch of thickness is 0.1 to 0.2 lb/ft2, (Figure 3 )

Figure 3 : Expanded polystyrene

(Source: www.homeconstructionimprovement.com)

Fesco Board
Fesco Board is a homogenous insulation board that is usually used as fire resistant. It
can resist damages that come from construction and maintenance. It must be kept dry
and its weight per inch of thickness is 0.77 lb/ft2, (Figure 4). Fesco board meets the
physical requirement of ASTM C 728.

Figure 4 : Fesco board

(Source: products.construction.com)

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ROOFING MEMBRANES

Roofing membrane is a type of roofing system, which is used on flat or nearly flat roofs
to prevent leaks and move water off the roof. Most of them are made from
thermoplastic or synthetic rubber modified bitumen. They are replacement for asphalt
roof systems. Most well-known membranes are EPDM (ethylene propylene diene
Monomer (M-class) rubber), TPO (thermoplastic polyolefin), PVC (Poly vinyl
chloride), BUR (Built-Up Roofing), Modified Bitumen and Liquid-Applied Membrane
and Metal roofing.
EPDM
EPDM is an elastic material with a different kind of applications. Great heat, ozone
and weather resistant, low cost, are important properties. Common thickness is: 45 mil
(0.29 lb/ft2), 60 mil (0.40 lb/ft2) and 90 mil (0.63 lb/ft2). It has an ability to retain in light
color. (Figure 5)
TPO and PVC Membranes
TPO and PVC membranes are thermoplastic membranes with good chemical and oil
resistant. The surfaces of them are in white color, and they are durable membranes.
According to 45 mil, 60 mil and 80 mil thickness the weights are (0.232 lb/ft2), (0.314
lb/ft2), (0.42 lb/ft2). (Figure 6)

Figure 5 : EPDM membrane

(Source: http://en.wikipedia.org)

Figure 6 : left: TPO membrane, Right: PVC membrane

(Source: www.arcat.com)

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The Role and Function of Thermal Insulation

Built-Up Roofing
A built-up roof (BUR) system is a composed of three materials. The bitumen, felts and
surfacing are the most-used materials in this membrane. There are two types of
modified bitumen systems such as APP (Atactic Polypropylene) and SBS (Styrene
Butadiene Styrene). These two differ in both installation processes, and they offer
some specific advantageous.
It is low-cost and poor chemical and oil resistant. It has been low resistant to
plant roots and there is needed the root barrier for the project to prevent growing the
root in the roof. (Figure 7)

Figure 7: BUR membrane

(Source: www.partnersroofing.com)

Modified Bitumen
Modified Bitumen is low cost membrane, and it is usually used for BUR systems. It has
been poor resistant to chemical and oil. Common thickness weight is around 1 to 1.75
lb/ft2. (Figure 8)

Figure 8 : Modified bitumen

(Source: www.frazierroofing.com )

Liquid-Applied Membrane

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Liquid applied membrane is becoming a popular choice for roofs, and it does not need
flames or other heat sources. This kind of membranes is based on flexible thermo set
resin systems such as polyester or polyurethane. Its weight with common thickness is
0.75 to 1.5 lb/ft2. (Figure 9)

Figure 9: liquid applied membrane

(Source: www.basf-cc.com.sg)

Metal Roofing
Metal Roofing is an expensive membrane and cost much higher than other types of
membranes but life time is more than 100 years, and this advantage makes it popular
roofing membrane in most buildings. The weight according to the most common
thickness is 1 to 1.5 lb/ft. (Figure 10)
PROTECTION MATERIAL

As mentioned earlier sometimes we need a protection layer to protect the insulation

layer from heat and chemical attack during installing roofing membrane GYPSUMBASED COVER BOARDS (DENS DECK OR DURABOARD), Fesco board, Extruded
Polystyrene, Fabrics are different kind of protection materials. Only gypsum based
cover boards is mentioned in the following, since others have been explained in
previous sections.

Figure 10: Metal roofing

(Source: www.metalroofingtips.com)

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Gypsum-Based Cover Boards (Dens Deck or Dura board)

Gypsum-based cover board is a highly mold resistant roof panel and consists of a
moisture-resistant, non-combustible core of specially treated gypsum with glass mat
facings. It delivers the highest performance ratings for fire, strength and moisture
resistance. It protects the insulator from heat and chemicals during adhering to the
insulation layers. Because of applied weight over green roof beneath and fasteners it
should be used to prevent damage to roof membrane. The three most common
thicknesses are 1/4-inch (1.1 lb/ft), and 1/2-inch (1.95 lb/ft), and 3/4-inch (2.5 lb/ft)
as shown in Figure 11.

Figure 11 : Gypsum board

(Source: www.cannon-roof.com)
MOISTURE-RETENTION MATERIAL

Some kind of green roof component needs to be capable of exposing to moisture.

These materials should absorb water when it is available. These products absorb
several hundred times their volume in water and discharge the water slowly. Moistureretention materials can remain wet for long periods. Most important moisture retention
materials are geo textile fabrics, gel pack and particles and Dimpled Mats.
Geo Textile Fabrics
Geo textile fabrics are the moisture-retention products. Horticulturists opinion is that
water stored in these products is actually available to the plants when this material is
positioned below root barrier and root plants intake water with contact. Example of this
kind of materials is the rock-wool blankets, which holds an impressive amount of
water. Although it depends on climate, it can be remaining wet for a long time, and it
can take effect in drought-tolerant feature of the green roof system. It is very durable
material which not only provides separation but also provides protective functions such
as large elongation before the brake, high puncture resistant. (Figure 12, Figure 13)

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The Role and Function of Thermal Insulation

Figure 12 : Rock wool blankets

(Source: www.safwatco.com)

Figure 13: Geo-textile fabrics

(Source: www.co.sheboygan.wi.us )

Gel Packs and Particles

Gel packs, and particles are packed in leaky pouches that are located near plant root
zones, and it can be blended to the growth media. It can absorb water hundred times
more than its volume and release the water slowly. It is useful for green roof plants but
should not rely on it as an irrigation system. Plants should be kept watching because
its rapid hydration can retain water from plants. The voids will be created in the soil
after releasing the water. Calculating based on volume capacity should be done on its
saturated weight.
Dimpled Mats and Filter Fabrics
Its place is under of growth media, an array of holes, which can be placed of water.
Although these are not heavy, for structural design process volume and weight of them
should be calculated. Entering of green roof particles to the drainage system and
stopping them from doing their work is a problem that can be solved by filter fabrics.
(Figure 14). They are very lightweight and usually contain chemical that repel root
growth. They can also act as root barriers.

Figure 14: Dimpled mats

(Source: products.construction.com)
ROOT BARRIERS
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Root barrier is placed so that structures, and plants may cohabit happily together. It
provides protection from root penetration and usually does not increase the weight of
green roof. Fabrics and Thermal Plastic are two common types of root barriers.
Fabrics have mentioned in previous sections, thermal plastic is in next section.
Thermal Plastic
Thermal plastic is more expensive than the fabric root barrier, and it is usually used in
intensive green roof projects, since it protects from root penetration: This material
should be used under the drainage layer and above waterproofing system.
WATERPROOFING

Buildings need waterproofing especially when green roof is implemented. Concrete is

not watertight on its own, so we need waterproofing materials. The conventional
system of waterproofing involves membranes. This relies on the application of one or
more layers of membrane (available in various materials: e.g., bitumen, silicate, PVC,
EPDM etc.) that act as a barrier between the water and the building structure and
preventing the passage of water. There is a liquid-applied sealant in the market which
has better adherence to a substrate.
Liquid-Applied Membranes versus Roll Goods
Liquid-applied materials like a hot modified rubber and elastomeric urethanes cure to
form a monolithic membrane with no seams (Luckett, 2009)[16]. In case of durability
felt and fabrics can be used with them. It is applied directly and after curing, has a very
good bonding to the concrete and this will prevent lateral movement of water between
membrane and roof deck. Since it has been maximum bridging capacity, liquid
material hasps problem is heavy penetration and cracks in the concrete. Roof
penetration is one of most important problem for liquid-applied materials and
penetration should be kept to a minimum. If it is unavoidable, flushing must be
installed. Water finds its way through concrete if the membrane damages. We should
have a plan for building expansion to decrease the risk of cracks and tears, which
comes by building movement. In the large project with large concrete structure liquidmaterials are less expensive than roll goods. Roll goods are produced in various
lengths and widths. These materials are installed by adhering, mechanically attaching,
or loose-laying and ballasting in place over the roof surface, and each of this method
has its advantage and disadvantages. Fully adhered membranes are typically more
expensive due to the cost of labor and material for the adhering process. Mechanically
attached roofing systems is a cost-saving alternative, but it is unsuitable or green roof
projects because the screw is used in this method, and it can disturb the surface by
green roof pressure on it. The last roofing configuration is loose-laid and ballasted
membrane the roof assembly is simply laid over the roof surface and then weighted in
place by ballast, in this case, the green roof system. This is the most cost-effective
means of roof installation, eliminating the labor and materials associated with fully
adhering or mechanically attached membranes.
In the case of a roof leak, loose-laid and ballasted roof installation has lateral
migration of water, making the source of the leak difficult to trace and increasing the
amount of water damage to the roof insulation and building interior.

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Another drawback is that ballast is required over the entire roof area to secure the
roofing system. However, in some cases we dont want to make all parts of the roof
green, and this can make the installation strategy unsuitable.
LOCATION OF THE INSULATION

As a mentioned earlier insulation layer is part of every building structure project. It can
be applied under or above roof materials. In many green roofs, projects are using
polyisocyanurate which is rigid and must be kept dry. So it should be installed under
the roof materials. If extruded polystyrene is used as insulation material, it can be used
as impervious and water proof material. The walls and curbs can be covered with an
insulation layer too.

Figure 15: Final Slope Roof (Luckett, 2009)

DISCUSSION AND CONCLUSION

In the previous sections, we discuss the kinds of material applied in the green roof and
some important issues, which should be concerned in the installation. Each of them
has positive and negative points. In the case of application according to kind of
desirable use, we should choose the most suitable kind. The high quality, reasonable
price and availability are the priorities characteristics. In choosing each of these
materials so many other issues should be kept in mind. In the case of physical issues,
the material should be chosen according to geographical and environmental
characteristics. For example, pesticide leakage from roof materials is one of the
issues which recently receive more attention. The material should be tested to
measure the amount of pesticide runoff to prevent from polluting the ground water. The
kinds of materials should be select for foundations and pathways, which have no
leach carbonates. So it is suggested to apply green roofing materials which have
environmentally friendly standards.
Furthermore the material should be chose and design in a way to prevent
unwelcome wildlife problems. In the case of plants preferably the plants should be
native but because the soils are not native soil (simply compacted, very heavy, etc.) it
would limit the green roof plant palette so its environment will be more limited in biodiversity.
Therefore, in a green roof different aspect of material should be respected, and
all the available verity should be considered to choose the best.

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REFERENCES

Barrio, E.P.D. 1998. Analysis of the green roofs cooling potential in buildings. Energy
and Buildings 27 (2): 179-193.
http://www.insulationireland.net/foam_board.htm
http://www.homeconstructionimprovement.com/foam-board-insulation-values/
http://www.homeconstructionimprovement.com/foam-board-insulation-values/
http://products.construction.com
http://en.wikipedia.org/wiki/File:EPDM_foil.jpg
[http://www.arcat.com/photos/genflex/107839.jpg
[http://www.partnersroofing.com/BUR.html
http://www.frazierroofing.com/products.php
[http://www.basfcc.com.sg/en/products/WaterproofingSystems/Pages/default.aspx
[http://www.metalroofingexpertstx.com/
http://www.cannon-roof.com/hunts/hpdens02.gif
http://www.safwatco.com
http://www.co.sheboygan.wi.us/images/lc/Geotextile%20Fabric.jpg
[http://products.construction.com
Luckett, K. 2009. Green roof construction and maintenance (GreenSource Books),
New York: McGraw Hill Professional.

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