Green Technologies and Sustainability 2 (2024) 100065
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Full-length article
Roofing systems and energy efficiency in low-rise buildings: A comparative
study across India’s diverse climates
Farheen Bano a ,∗, Mohammad Tahseen b
a
b
Faculty of Architecture and Planning, AKTU, Lucknow, India
Department of Architecture, Government Polytechnic, India
ARTICLE
INFO
Keywords:
Building envelope
Energy-efficient roofing
Green roofs
Cool roofs
Energy efficiency
Climate-specific recommendations
ABSTRACT
The building envelope is the interface between the external atmospheric conditions and the indoor environment. It contributes to approximately 60%–70% of the heating and cooling load. The building envelope
constitutes walls, fenestrations, and roofs from which thermal transfer from the roof is significantly very high
compared to walls in low-rise buildings.
This research paper aims to provide recommendations for energy-efficient roof design considering roof
form, material, and external coating suitable for various climate conditions of India. The paper’s methodology
consists of a literature review of related research papers, learnings from the roofing system of energy-efficient
building case studies, and all possible energy-efficient roofing systems that would be simulated for energy
efficiency and thermal comfort in five climate types of India. The expected outcome of this paper would be
in the form of recommendations for roofing systems in different climate type and their potential for energy
saving from the highest to the lowest. This research would be done in three stages viz, Step-1: Literature
Review and case study of best practices: A review of the related literature and best practices examples would
be done to formulate the maximum possible cases for the simulation. Step-2: The roofing systems, including
building form, material (Thermal and insulation), and finishes (reflectance), would be simulated one by one for
various climate types of India (composite, hot & dry, warm and humid, moderate and cold) to optimize energy
efficiency and payback period. Step-3: Special roof types like Green roofs, cool roofs, Photovoltaic roofs, roof
ponds, and the like are simulated and compared for their effectiveness in selected climate types. Based on the
literature review, simulation results, and analysis, the recommendations are framed for energy-efficient roofing
systems in the selected climate type with respect to heat transfer through the roof and thermal comfort.
1. Introduction
Buildings are significant energy consumers in their construction,
running, and maintenance phases. In India, 31% of energy is used in
residential and commercial buildings from the total energy consumption (Bano & Kamal, 2016). An air-conditioned building consumes 55%
of its energy in its use phase to make the building comfortable with
the heating, ventilation, and air conditioning (HVAC) system. The load
on HVAC comes from the heat gain or losses through the building
envelope comprising the roof, wall, and windows. Heat transfer from
the roof is very significant in low-rise buildings compared to high
rise. It contributes approximately 26% to the load of HVAC (refer
Fig. 1). Hence, energy efficient roof design can reduce the heat transfer,
thus the load on HVAC. It has been estimated that a 10 to 40%
reduction in air conditioning expenditure can be achieved through the
climate-responsive design of a roof [1].
India has diversified climate types distributed all over. Hence, one
roof type could not be effective in all climates. This research paper aims
to find a suitable roofing system for various climate types of India, viz.
hot and dry, warm and humid, temperate, composite and cold (ECBC,
2017). The roofing system comprises roof form, material, and finishes.
The simulation has been carried out initially for optimum roof form,
then materials and finishes identified through literature review. The
cases made for the simulation were checked for all the climate types
and cities selected, as given in Table 1.
2. Challenges in implementing roofing systems across diverse climatic zones
Implementing roofing systems tailored to diverse climatic zones in
India presents several challenges that warrant thorough consideration.
∗ Corresponding author.
E-mail addresses: bano.farheen@foaaktu.ac.in (F. Bano), mtahseensiddique@yahoo.co.in (M. Tahseen).
https://doi.org/10.1016/j.grets.2023.100065
Received 7 November 2023; Received in revised form 1 December 2023; Accepted 26 December 2023
Available online 29 December 2023
2949-7361/© 2023 The Authors. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC
BY license (http://creativecommons.org/licenses/by/4.0/).
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
importance of aligning roofing solutions with regional preferences and
regulations.
Incorporating these challenges into our research aims to provide
a comprehensive understanding of the complexities involved in implementing roofing systems across India’s diverse climatic regions.
Acknowledging and addressing these limitations will facilitate more
informed decision-making processes for stakeholders involved in sustainable construction practices.
3. Methodology
The research was carried out in the following steps:
1. Initially, all literature studies are done. It includes data collection from research papers, the internet, and books.
2. This review gives an insightful overview of the energy-efficient
roof to understand the energy-efficient roof technology. Moreover, which roofing system is efficient in which climate type.
3. Review of Vernacular roofing system in different climatic condition to understand the Cultural and social aspects.
4. Lastly, selected roof form, materials, and finishing techniques
would be simulated in different climate types one at a time.
Fig. 1. Heat Gain through various Building Envelope Components (a) in multistoried
buildings (b) in a single storied building.
Source: Bano & Kamal (2016).
Table 1
Climate type and selected cities.
Source: ECBC (2017).
Climate type
City
Hot and dry
Warm and humid
Temperate
Composite
Cold
Ahmedabad
Mumbai
Pune
New Delhi
Srinagar
4. Literature review
One of the primary challenges lies in assessing the suitability of
roofing systems in distinct climatic conditions. Extreme temperatures,
variable precipitation levels, humidity, and other environmental factors
significantly influence the efficacy of these systems. Understanding
how these elements impact the performance and durability of roofing
solutions is imperative for successful implementation.
When we consider the residential and commercial buildings and
their climate, no two buildings are equivalent to energy consumption.
As a result, multiple types of roofs are designed to suit various building
designs and climatic conditions.
Buildings roofing system depend upon their climatic conditions.
A lot of engineers and architect works on the efficiency of a roof
in a particular climate. To understand, how different roofing system
helps reduce energy consumption in the building, a study from 10
sources from each climate type has been carried out in this research
paper, which includes published research papers and books available
on related topics. The data collected from these sources has been
systematically presented in Table 1.
The data has been broadly categorized into various parameters
(such as location, climate, roof type, roof form, energy saving). Further
comparative analysis of all these studies on these parameters provides
us with the roofing systems’ idea.
2.2. Material availability and suitability
4.1. Hot and dry
The availability and suitability of roofing materials within different regions pose notable challenges. Disparities in material accessibility, cost-effectiveness, and compatibility with local construction
practices influence the feasibility of adopting specific roofing systems.
This section will delve into how these factors affect the practicality and
widespread adoption of energy-efficient roofing solutions.
Recent researches of roofing system in hot and dry climate have
been reviewed and listed down in Table 2 considering their roof form,
material and finishes together with the building typology, city and its
energy saving potential.
Following inferences has been drawn from the literature review of
roofs in hot and dry climate:
This section outlines the multifaceted limitations and practical challenges associated with deploying specific roofing solutions across varied
regions.
2.1. Climatic suitability
1. Roof Form- Flat roof, vaulted roof and domed roof can be used
in hot and dry climate, out of which vaulted and domed roof
are the most efficient roof forms (without any insulation). In
the domed roof, heat gain decreased by 25%, despite the dome
covering only 60 to 70% of the roof [2]. In the vaulted roof, the
decrease in roof gains is of more excellent value than with the
domed roof, where the vaulted roof covers the entire 100% of
the roof area [3]. This leads to a decrease in the average indoor
temperature in August of close to 1.5 ◦ C.
2. Material- Reinforced Cement Concrete (RCC) is the basic structural material of the roof. Insulating materials like Expanded
polystyrene (EPS), Extruded polystyrene (XPS), polyurethane
foam (PUF), Glass fiber, rockwool and water have been used
above the roof to reduce heat gain [1,4,5]. The lowest U-value
can be achieved through PUF and economical insulated roof
solution can be achieved by using rockwool [6,7]. Phase change
2.3. Maintenance and longevity
Long-term maintenance requirements and the durability of roofing
systems under diverse environmental stresses are crucial considerations. Addressing challenges related to maintenance needs, potential degradation, and the longevity of these systems within different climatic zones is essential for evaluating their sustainability and
practicality.
2.4. Cultural and regulatory considerations
Local cultural preferences, architectural styles, and regulatory frameworks significantly impact the acceptance and adoption of roofing
systems. Discussing the challenges arising from these factors will shed
light on the barriers to widespread implementation and highlight the
2
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 2
Literature review of roofs in hot and dry climate.
Building
type, city
Roof type
Materials (base
material, insulation,
finishes) with
thickness
Residential,
CairoAlexandriaAswan
Sloped
Reinforced concrete
150MM
Residential
Cairo, Egypt
Vaulted
roof Non
insulated
Reinforced concrete
150MM, Soft sand
70MM, cement
mortar20MM
Albedo bright white
paint (0.1 visible
absorptance) 10MM
Residential,
Iraq/Hyderabad
Flat,
Insulation
School,
Mexico
Aswan,
Egpt/Iraq
U-value
Energy
savings
Construction details
Reference
12.5%
Mahmoud &
Ismaeel (2019)
3.15
32%
Dabaieh et al.
(2015)
Insulation of 50 mm
above 150 mm RCC
roof
0.6–
0.261
16.18
Dhaka et al.
(2012)
Najim & Fadhil
(2015)
Flat, Green
roof
Characteristics of
the soil: Specific
heat = 1000
(J/kg-K), D =
400 kg/m3
Characteristics of
the plants: Leaf area
index = 4, height of
plants = 0.1 m, leaf
emissivity = 0.9
0.3–.09
31.61 and
39.74% of
energy
saving
Ragab &
Abdelrady (2020)
Roche (2009)
Farrell et al.
(2012)
Flat, PCM
40 mm of
RT31-PCM
20 mm Paraffin wax
40%
13.9%
Elawady et al.
(2022)
Al-Yasiri & Szabó
(2021)
Residential,
Kerman city
Iran shiraz,
Iran
Flat, Roof
pond
Pond height
50–100 mm
58.1%
material is also used as an insulating material above or below
the RCC roof as heat exchange and reduce energy consumption
by 13 to 40% with variation in PCM depth [8,9].
3. Finishes- Cool Roofs, Green roof, Roof pond, shaded roof ponds,
Photovoltaic roof, Biosolar roofs and double skin roofs are the
options for energy efficient finishes over the roof to heat transfer
in hot and dry climate [1]. Out of these Roof pond, Green roof,
and Cool roof are the most efficient roofing type. Cool roof and
Goudarzi &
Mostafaeipour
(2017)
Abuseif & Gou
(2018)
Photovoltaic roof has the lowest payback time. The cool roof
is cheaper and can reduce 50 to 65% energy consumption in
a building. Green roof reduces 30 to 50% energy consumption,
minimize ambient and indoor temperature in a building. But
has high-cost and high payback time. Finishing like high albedo
bright white paint, ceramic roof tile reddish or white colored
can be used in cool roof. In the green roof, we can use concrete
slab (100-200MM) and metal deck roof for the base material.
3
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 3
Literature review of roofs in warm and humid climate.
Building
type, city
Roof type
Materials (base
material, insulation,
finishes) with
thickness
U-value
Energy
savings
Construction details
Reference
Experimental
cell,
Venezuela
Flat, Roof
Ponds
Galvanized steel
120MM, Water
100MM, Polystyrene
covered by glass
fibber 50MM
41 to 66
[12]
Residential
and
commercial,
Italy
Pitched,
ventilated
roofs
Brick tiles 30MM,
Wooden planking
10MM, Air gap
100MM, Rigid
fiberglass panels
40MM, Cement
mortar 10MM
Up to 50%
[13]
Residential,
Thailand
Pitched roof
solar
chimney
Fastening a gypsum
board to the lower
part of the rafter,
the air ducts with
thickness of
14–16 cm are
formed under the
roof tile.
Residential
Madurai,
India
Flat, Green
Roofs
Concrete slab
200MM, Water
Proof Membrane,
Insulation, Drainage
board 0MM,
Moisture Retention
layer 5MM, Soil
100M
0.4
40%
[15]
Residential
Madurai/
Mumbai,
Flat, Cool
roof
Concrete slab
100MM , Lime
concrete (brick bats)
50MM, elastomeric
white coating with
solar reflectance 0.6
Concrete slab
1000MM, Plaster
20MM, Extended
polystyrene
insulation , plaster
board 90MM
2.44,
0.618
25%
economical
[15]
[16]
[14]
Over its waterproof membrane was placed, then root protection
barrier, Rigid insulation, Aeration layer, water retention layer,
filter fabric and lastly engineered soil with planting [10,11].
Following inferences has been drawn from the literature review of
roofs in warm humid climate:
1. Roof Form- The pitched roof and flat roof are the best options in
humid climate due to high humidity and rainfall [17].
2. Materials- We can use concrete as a base material for the cool
roof and Insulatoring materials like PUF, rockwool, water, etc
[4]. Lesser the U-value more the energy efficiency in building, while rockwool turns out to the economical solution with
optimum energy efficiency [18].
4.2. Warm and humid
Recent researches of roofing system in warm humid climate have
been reviewed and listed down in Table 3 considering their roof form,
material and finishes together with the building typology, city and its
energy saving potential.
4
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 4
Literature review of roofs in warm and humid climate.
Building
type, city
Roof type
Materials (base
material, insulation,
finishes) with
thickness
U-value
Energy savings,
cost
office,
London/
Banglore
Flat Cool
roof
The cool roof paint
was selected from
ABOLIN (Cool Barrier
012 – CB012) with an
SR value of 0.6 and
infrared emittance of
0.88.
0.6
8.5%–
10%
Payback period
of cool roof
cost s 2.78
[19]
[16]
residential,
Italy/Italy
Pitched
roof Cool
roof
Clay tile, White
engobe, Thin
pigmaentsl
18%,
[20]
[21]
office,
Europe
Flat,
Cool/
Green
roof
Concrete slab
200MM, WATER
PROOF MEMBRANE,
Insulation, Drainage
board 50MM,
Moisture Retention
layer 25MM, Soil
100M
10%
[22]
[23]
3. Finishes- Cool Roofs, green roof, ventilated roofs, Photovoltaic
roof, Biosolar roofs are the options in which Cool Roofs, ventilated roofs, and Photovoltaic roof are the most energy-efficient
roofing system [1]. Green roof minimize ambient and indoor
temperature in a building. Ventilated roof allow the hot air to
escape keeping roof cooler. Energy saving is slightly lower in
this climate than the hot and dry climate because uncomfortable
hours are low in this climate. Ventilated roofs can reduce up
to 50% energy consumption. Green roofs reduce more heat
gain compared to the cool roofs and can reduces 40% energy
consumption.
Construction details
Reference
4.4. Composite
Recent researches of roofing system in composite climate have been
reviewed and listed down in Table 5 considering their roof form,
material and finishes together with the building typology, city and its
energy saving potential.
Following inferences has been drawn from the literature review of
roofs in warm humid climate:
• Roof Form- A flat roof is preferred in composite climate for both,
reducing heat loss in winters, and heat gain in the summer time.
• Materials- Insulated roofs can reduce heat transfer in this type of
climate type.
• Roof Finishes - Cool roof and Green roof are extensively used in
composite climate coupled with PV panels.
4.3. Temperate
4.5. Cold climate
Recent researches of roofing system in temperate climate have been
reviewed and listed down in Table 4 considering their roof form,
material and finishes together with the building typology, city and its
energy saving potential.
Following inferences has been drawn from the literature review of
roofs in temperate climate:
Recent researches of roofing system in cold climate have been reviewed and listed down in Table 6 considering their roof form, material
and finishes together with the building typology, city and its energy
saving potential.
Following inferences has been drawn from the literature review of
roofs in warm humid climate:
1. Roof Form- The pitched roof and flat roof are the best options in
moderate climate due to rainfall [20].
2. Materials- Concrete slab (100–200 MM) and metal deck roof with
insulating material can be used [16].
3. Finishes- Cool roofs and green roofs works best in this climate
type. Cool roof saves 10 to 20% with some time heating energy
penalty 10% [20]. Green roof reduces 10 to 15% energy consumptions in the building. Biosolar roof is also very useful can
also be used [22].
• Roof Form- A flat and piched roof is preferred in cold climate for
passive heating.
• Materials- Insulated and double skin roofs can reduce heat transfer
in this type of climate type. In cold climate heat loss should
be reduced, which is done by an airtight envelope and good
insulation. Insulation play a important part in cold climate roof.
High thermal mass i.e. Concrete slab, insulation with Extended
polystyrene, PUF.
• Roof Finishes- Skylight roof with louveres could in increasing heat
gain in a building.
5
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 5
Literature review of roofs in composite climate.
Building
type, city
Roof type
Materials (base
material, insulation,
finishes) with
thickness
U-value
Energy
savings,
cost
Construction details
Reference
Office,
Delhi/
Pantnagar
Flat Cool
roof
Concrete slab 100MM
Gypsum plastering
12MM, Sand and
gravel 20MM, White
paint with reflectance
0.70
0.261
16.04
[4]
[16]
[24]
Composite
climatic,
Raipur ,
Chhattisgarh
state
Flat
Green
roof
Concrete slab
200MM, WATER
PROOF MEMBRANE,
Insulation, Drainage
board 50MM,
Moisture Retention
layer 25MM, Soil
100M
Dec. temp.
by 40 C
[25]
[23]
Table 6
Literature review of roofs in cold climate.
Building
type, city
Roof type
Materials (base
material, insulation,
finishes) with
thickness
U- value
Energy
savings, cost
Residential,
Australia
Flat
Insulated
Roofs,
double skin
roof,
skylight
roof
RRC slab wih air gap.
Glass roof with
louvers
–
10%–30%
[1]
[26]
[27]
Commercial,
Ottawa,
Canada
Flat, Vacum
insulated
roof
RCC slab Vacuum
insulated panel above
it
0.4
20%
[28]
5. Recommendation of roofing assembly in Indian green building
rating system and building codes
Construction details
Reference
determines their assignment to these criteria. National building Codes
(NBC) and Energy Conservation Building codes also recommends design buildlines for energy efficient design Guidelines for roofing systems
in Indian climate types. The recommendation by them have been listed
in Table 7.
Roofs not covered by solar photovoltaics, solar hot water, or any
other renewable energy system, or uses and services that render it
improper for the purpose shall be either cool roofs or green roofs. For
qualifying as a cool roof, roofs with slopes less than 20◦ shall have an
initial solar reflectance of no less than 0.60 and an initial emittance
no less than 0.90. Solar reflectance shall be determined and emittance
shall be determined. For qualifying as a Green roof, roof areas shall be
covered by living plants.
Indian green building rating systems are mainly Green Rating for
Integrated Habitat Assessment (GRIHA) and Indian Green Building
Council (IGBC). Building codes applied for energy efficiency are Nation
building code 2016 and Energy Conservation Building Code (ECBC).
GRIHA was chosen as the National Rating System (NRS) after being
modified in 2015 by MNRE, Government of India. It can be adapted
over different climatic zones of the country, including various kinds
of buildings. Both GRIHA and IGBC are working at the national level
and have a list of criteria. The relative significance of several points
6
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 7
Recommendations by rating systems and Codes.
Rating
system/codes
Hot and dry
Warm and humid
GRIHA
Heat transfer from roof should be reduced by 90%. Cool roofs recommended
IGBC
U value of Roof assembly of 1–1.2 W/m2 K.
[30]
ECO-NIWAS
Cool roof with 50% reflectance.
U-Value should not exceed 0.58 W/m2 K
[31]
[32]
NBC/ECBC
School < 10,000
m2 AGA
0.47
0.47
Temperate
0.47
Composite
Cold
Reference
[29]
0.47
0.33
[31]
[33]
Table 8
Vernacular architecture.
Climate
type
Hot and dry
Warm and humid
Temperate
Composite
Cold
Case Study
Bhunga house, Gujarat
Kutch region
Padmanabhapuram
Palace in Kanyakumari
district of Tamil Nadu
Guthu houses, traditional
homes of bunt
community of coastal
Karnataka
Toda hut
Sofi (Traditional) houses in
Ladakh
Form &
material
circular mud walls with a
conical thatched roof.
Have inner diameter in
between 3 m to 10 m
Pitched roof made up of
materials like stones,
timber, clay and palm
leaves, etc. In which
timber is the prime
structural material.
a steeply pitched roof
with Mangalore tiles,
consists of single &
double-storey building
around a huge courtyard.
pent-shaped structure
created with native
materials of lashed
bamboo sticks and
fasteners of rattan, the
bamboo stalk’s pliable
stems. Local materials like
thatch from straw or rods
and local grass, stone,
timbers, and mud are
used.
Flat roof made up of local
materials like mud, clay,
wood, sunburnt bricks,
willow, and timber.
Roof
The roof is made of the
wooden top dome where
bamboo sticks are fixed
with a thick layer of grass
put on a roof and tied
together. The walls cannot
bear the roof’s wood
beam, which runs across
space diagonally and rests
on two wooden posts
Padmanabhapuram
Palace has Pitched roof
with proper ventilation.
Clay tiles are used as a
finished roofing material
supported with wooden
rafters and then pillars
The Guthu house roof is
made up of Mangalore
tiles, terracotta tiles and
glass tiles to let in light
supported by wooden
carved pillars.
Toda hut’s roof consists of
local wooden rafters over
which Thick thatch is
placed made up of unique
local grass.
the roof is made up of
willow joints placing over
the rafters, then applying
the traditional layering of
mud and clays. Layers of
Mud and clays in the roof
provide good insulation and
absorb heat during a sunny
day and slowly radiate it
during the cold nights
[34]
[35]
[36]
[36]
[37]
View
Details
Reference
7
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 9
Simulation inputs for a Classroom for 40 students.
Room Type
Classroom for class 5 students
Occupancy
40 students
Details
Reference
Occupancy hours
8am–5pm
Area
72–80 m2
1.8–2 m2 /pupil
Neufert et al. (2012)
Dimensions
7.2 m × 10 m
If the windows are all
on one side, the max.
room depth is 7.20 m
Neufert et al. (2012)
Infiltration rate
13 cfm/person, 6.5 l/s person
For age 9 year plus
NBC (2016)
LPD
15.1 W/m2
NBC (2016)
Table 10
Simulation cases: Variations in base case to achieve energy-efficient roofs.
Type
Variations
Roof Forms
Flat
Pitched
Vault
Dome
Basecase
30◦ inclined (NS and EW orientation)
NS and EW orientation
In the center
Material
Insulating Material
Double skin roof
water
50 mm PUF and rockwool above deck
100 mm air
50 mm water
Finishes
Cool roof
Green roof
PV roof
Roof pond
Tiles and cool roof paint
Intensive
PV solar panels
100 mm water
6. Vernacular roofing system
The primary purpose of energy efficient to restrict heat transfer
through roof and to make indoor conditions comfortable. Table 11
shows the simulation results on altering selected roof forms in hot and
dry, warm and humid, moderate, composite and cold climate.
Pitched roof in NS orientation has the most negligible heat gain in
hot climates like hot and dry, warm and humid and temperate climate
types; however, if PPD is compared, NS vaulted, and dome roofs seem
the most appropriate option for hot climates to make indoor conditions
comfortable. The composite climate has extreme summers and winter
seasons; thus, heat gain in summer and heat losses in the winter season
is calculated through simulation. On simulation, it is being observed
that apart from the flat roof, all roof forms are energy efficient in a
composite climate when compared based on heat transfer. However, a
dome roof could be optimum for heat transfer and thermal comfort in
both hot and cold seasons. In a cold climate, NS oriented pitched roof
is the most efficient roof based on heat transfer during cold seasons and
thermal comfort.
Vernacular Architecture is the architecture that has been tested for
its efficiency for ages. Vernacular Architecture of different climate types
of India has been analyzed for its techniques of a roofing system to
achieve energy efficiency (see Table 8).
7. Simulation
After a literature review of the roofing system in different climate
types in India, simulation has been conducted to estimate the best
possible roof form, material and finishes. The simulation was carried
out initially for optimum roof form and then materials and finishes
(identified through a literature review) given in Table 9. The cases
made for the simulation were checked for all the climate types listed
above and cities selected as given in Table 1. A classroom for 40 students has been considered a base-case with simulation input parameters
adopted from codes and standards as listed in Table 9 (see Figs. 2 and
3).
9.2. Roofing material simulation results and discussion
8. Simulation cases
Polyurethane foam (PUF), Rockwool, air and water, readily used
insulating materials as insulating material observed through literature
review, are selected for roof insulation. The thickness of these materials
have been kept as per the best practices i.e. thickness for PUF and
Rockwool is kept 50 mm whereas air and water as 100 m (see Table 12).
Simulation shows that PUF is the best insulation material in all climate types for reducing heat transfer and thermal comfort. In contrast,
water is the most inefficient insulating material. An air gap as insulation
can be an economical solution to reduce heat gain and increase thermal
comfort in all climate types. In a hot and dry climate, the variation in
thermal comfort on adding insulation is low compared to temperate
and cold climates (see Table 13).
The base-case model of the classroom has been simulated in different climate types of India discussed above to identify optimum
roof type in terms of roof type, material and finishes. The analysis
was done based on overall heat transfer in kWh from roof and the
predicted percentage of dissatisfied (PPD) index. It estimates how many
occupants in space would feel dissatisfied with the thermal conditions.
All occupied areas in a space should be kept below 20% PPD to ensure
thermal comfort according to the known standards [38] (see Table 10).
9. Result and discussions
9.1. Roof form simulations results and discussion
9.3. Simulation results of roofing finishes
Simulation of roof form was performed to calculate the variation in
heat transfer through flat, pitched, vaulted, and dome roof (Fig. 4) in
various climate types of India and associated PPD values.
Over flat roof three types of roof finishes have been selected for
comparative study viz, cool roof, green roof and roof pond. Cool roof
8
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 11
Simulation results for annual heat gain through roof forms in different climate types.
Simulation data
Charts
Hot and dry- Ahmedabad
Roof form
Heat gain through
the roof in kWh
PPD%
Flat
3531.52
56.85
Pitched roof NS
467.76
59.07
Pitched roof EW
899.18
58.86
Vaulted roof NS
4530.38
51.79
Vaulted roof EW
5001.29
51.91
Dome
3,227.30
52.96
Roof form
Heat gain through
the roof in kWh
PPD%
Flat
5721.67
63.33
Pitched roof NS
2128.65
65.14
Pitched roof EW
2553.5
65.57
Vaulted roof NS
6391
56.43
Vaulted roof EW
6965.13
57.29
Dome
4,806.88
58.04
Roof form
Heat gain through
the roof in kWh
PPD%
Flat
5374.18
46.43
Pitched roof NS
2520.77
46.13
Pitched roof EW
2547.75
48.05
Vaulted roof NS
5853.89
38.2
Vaulted roof EW
6056.01
38.47
Dome
4671.18
39.1
Warm and Humid- Mumbai
Temperate- Bengaluru
Composite- New Delhi
Roof form
Heat gain through
the roof in kWh
PPD%
Heat losses through
the roof in kWh
Flat
5374.81
50.03
2144.18
Pitched roof NS
1492.75
51.07
1868.3
Pitched roof EW
1584.79
51.76
1391.53
Vaulted roof NS
2612.46
44.28
1561.18
Vaulted roof EW
2645.95
45.47
1244.17
Dome
1817.24
45.28
2152.99
Roof form
Heat gain through
the roof in kWh
PPD%
Heat losses through
the roof in kWh
Flat
2876.37
48.46
4921.64
Pitched roof NS
2250.42
49.15
3028.46
Pitched roof EW
2340.75
46.34
3884.42
Vaulted roof NS
5062.28
42.01
5011.32
Vaulted roof EW
6710.24
44.26
4361.27
Dome
3562.84
42.88
4960.54
Cold Srinagar
9
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Fig. 2. Basecase: (a) Plan of a classroom (b) model in design-builder.
Table 12
Roof assembly in the simulation program.
Roof assembly
Insulating material
Polyurethane foam (PUF) (50 mm
thickness)
Rockwool (50 mm thickness)
Air (100 mm thickness)
Water (100 mm thickness)
U-value of material
(W/mK)
0.028
0.033
0.3
0.6
Specific heat
(J/kgK)
1470
710
1000
4190
Density Kg/m3
30
100
1000
1000
U value of roof
assembly (W/m2 K)
0.492
0.568
1.728
2.428
Fig. 3. View of model in designbuilder.
and green roofs are popularly used in hot climates to reduce heat gain
in buildings through roofs. Roof pond is also a passive strategy used to
reduce heat gain through roofs. The properties of these types of roofs
are given in Table 14. These strategies are compared through simulated
by placing them above flat roof in selected climate types.
Table 14 shows the simulation results and its analysis in terms of
the percentage of decrease in heat transfer through roofs and increase
in thermal comfort. Graphs show that a decrease in heat transfer is
directly proportional to an increase in thermal comfort. Cool roofs
perform outstandingly in hot climates like hot and dry, warm and
10
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 13
Simulation results for annual heat gain through roofing materials in different climate types.
Simulation data
Charts
Hot and dry - Ahmedabad
Insulating
material
Heat gain through
the roof in kWh
PPD%
no insulation
3531.52
56.85
PUF
313.25
53.38
Rockwool
365.53
53.45
Air
1372.63
54.55
Water
2247.04
55.74
Heat gain through
roof in kWh
PPD%
Warm and Humid- Mumbai
Insulating
material
no insulation
5721.67
63.33
PUF
689.64
57.21
Rockwool
760.01
57.43
Air
2491.46
60.78
Water
3797.3
62.55
Heat gain through
roof in kWh
PPD%
Temperate- Bengaluru
Insulating
material
no insulation
5468.79
46.43
PUF
663.06
36.71
Rockwool
763.74
37.02
Air
2425.86
42.14
Water
3595.32
44.43
Composite - New Delhi
Roof form
Heat gain through
roof in kWh
PPD%
Heat losses through
roof in kWh
no insulation
5374.81
50.03
2144.18
PUF
573.71
42.6
486.18
Rockwool
778.18
42.83
667.24
Air
1477.45
45.65
2411.61
Water
3559.08
47.22
1653.49
Heat gain through
roof in kWh
PPD%
Heat losses through
roof in kWh
Cold - Srinagar
Roof form
no insulation
2876.37
48.46
4921.64
PUF
374.65
35.95
1421.86
Rockwool
430.17
36.4
1599.93
Air
1195.06
41.56
3233.76
Water
2110.79
43.53
4009.83
11
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Fig. 4. Variations in roof form simulated in design builder.
Table 14
Roofing Finishes in the simulation program.
Cool Roof
Green Roof
Roof Pond
U-value of Roof
(W/m2 K)
4.078
1.4
1.78
Properties of
Roof Finishes
Solar Reflectance: .95
Thermal Emittance: 0.91
Solar Reflective Index: 122
Thermal Conductivity (W/m K) : 0.9
Density (kg/m3 ) : 1850
Specific Heat (J/kg K) : 850
Thermal emissivity : 0.65
Minimal stomatal resistance (s/m) : 180
Solar Absorptance : 0.35
Leaf reflectivity : 0.22
Leaf emissivity : 0.95
Soil thickness (m) : 0.3
Height of plant (m) : 0.3
Thermal Conductivity (W/m K) : 0.6
Density (kg/m3 ) : 997
Specific Heat (J/kg K) : 1000
Roofing Finishes
The pitched roof is the best option in moderate climates due to rainfall with insulation, or a double roof finished with cool roof technique.
The total U-value of the roof in requirements for ECBC Compliant
Building should be 0.33 W/m2 K. In a composite climate, there are both
extreme heat and cold, so there should be a high reflectance surface on
the top of the roof along with high thermal mass and high insulation
protected by hot and cold both. A highly insulted dome roof with a cool
roof coating or green roof is recommended in this climate type.
humid, and temperate, followed by roof ponds. Heat transfer reduction
and thermal comfort achieved through a green roof in a composite and
cold climate are the highest. Hence cool roof is suitable for hot and dry,
warm and humid, and temperate climates, while green is suitable for
composite and cold climate types (see Table 15).
10. Conclusion
This research establishes that roof form, material, and finishes
contribute significantly to the heat transfer through the roof inside
the building and thermal comfort. The literature review, followed by
the simulation, helps formulate the recommendation for roof design in
different climate types of India in table IX. The total U-value of the
roof requirements for ECBC Compliant Building should be 0.33 W/m2 K
except for the cold climate. The U-value for roof in cold climate is
recommended 0.28 W/m2 K (see Table 16).
Vaulted and domed roofs are the most efficient roof forms in hot and
dry climates (without any insulation). Insulators (Resistive insulators)
like polyurethane, Rockwool, air and water can be used. The lowest Uvalue can be achieved by corrugated fibrous cement with 50 mm PUF.
Green roofs and Cool roofs are the most efficient roofing type. Cool
roof with finishes like high albedo bright white paint, ceramic roof tile
reddish or white colored is recommended. The total U-value of the roof
requirements for ECBC Compliant Building should be 0.33 W/m2 K
The pitched roof is the best option in humid climates due to high
humidity and rainfall with light material and ventilated roof. Cool roofs
and PUF insulation reduce heat transfer inside the building. The total
U-value of the roof requirements for ECBC Compliant Building should
be 0.33 W/m2 K. Energy saving is slightly lower in this climate than in
the hot and dry climate.
An airtight envelope with insulation can reduce heat loss in cold
climates. Green roof works best in this climate. Pitched roofs and flat
roofs are the best options in the cold climate.
11. Future research directions
In concluding this study, critical areas for future research in advancing energy efficiency within building envelopes emerge. Future
investigations should prioritize the development of advanced building materials tailored to diverse climates, explore the integration of
smart technologies for optimized energy usage, and delve deeper into
innovative design strategies to minimize energy demand while maximizing occupant comfort. Additionally, comprehensive lifecycle assessments and studies examining socio-economic implications are crucial for evaluating long-term sustainability and fostering widespread
adoption of sustainable construction practices. Collaboration among
multidisciplinary teams and fostering knowledge-sharing platforms will
also play a pivotal role in accelerating advancements in sustainable
building technologies and methodologies.
12
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 15
Simulation results for annual heat transfer and thermal comfort through roof finish in different climate types.
Simulation data
Charts
Hot and dry - Ahmedabad
Insulating
material
Heat gain through
the roof in kWh
PPD%
Flat roof
3531.52
56.85
Cool roof
−5123.15
45.1
Green roof
−1759.68
49.43
Roof Pond
−2716.79
47.4
Insulating
material
Heat gain through
the roof in kWh
PPD%
Flat roof
5721.67
63.33
Cool roof
−3472.86
48.46
Warm and Humid- Mumbai
Green roof
−1033.22
53.61
Roof Pond
−1813.76
51.04
Insulating
material
Heat gain through
the roof in kWh
PPD%
Flat roof
5468.79
46.43
Cool roof
−4438.91
27.83
Temperate- Bengaluru
Green roof
−1453.46
30.86
Roof Pond
−2371.04
29.06
Composite - New Delhi
Roof form
Heat gain through
the roof in kWh
PPD%
Heat losses through
the roof in kWh
Flat roof
Cool roof
5374.81
50.03
2144.18
−791.98
42.23
4119.05
Green roof
−704.63
39.89
1348.37
Roof Pond
−401.12
40.58
2333.12
Roof form
Heat gain through
the roof in kWh
PPD%
Heat losses through
the roof in kWh
Flat roof
2876.37
48.46
4921.64
Cool roof
−1231.83
47.72
10,056.00
Green roof
−440.69
36.64
2834.26
Roof Pond
−666.94
40.64
5820.13
Cold - Srinagar
13
F. Bano and M. Tahseen
Green Technologies and Sustainability 2 (2024) 100065
Table 16
Recommended roof forms, materials and finishes in different climate types of india.
Climate type
Hot and dry
Warm and humid
Temperate
Composite
Cold
N
V.H
H
M
N
L
H
V.H
N
V.H
H
M
N
H
M
M
L
N
H
M
M
L
N
H
M
M
L
V.H
M
M
H
V.H
M
L
V.H
M
ROOF FORM
Flat
Pitch
Vault
Dome
N
L
H
V.H
N
V.H
H
M
No insulation
PUF
Rockwool
Air
Water
N
H
M
M
L
N
H
M
M
L
Cool Roof
Green Roof
Roof Pond
V.H
M
M
V.H
M
M
ROOF MATERIAL
ROOF FINISHES
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Farheen Bano: Writing – review & editing, Writing – original draft,
Visualization, Software, Resources, Methodology, Investigation, Data
curation, Conceptualization. Mohammad Tahseen: Writing – review
& editing, Validation, Formal analysis.
Declaration of competing interest
I hereby declare that the disclosed information is correct and that
no other situation of real, potential or apparent conflict of interest
is known to me. I undertake to inform you of any change in these
circumstances, including if an issue arises during the course of the
meeting or work itself.
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