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Parametric study of the impact of Impact of

building
building envelope systems on envelope
systems
embodied and operational carbon
of residential buildings
Amneh Hamida, Abdulsalam Alsudairi and Khalid Alshaibani Received 8 August 2020
Revised 9 January 2021
Department of Architecture, College of Architecture and Planning, 4 March 2021
Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia, and Accepted 19 March 2021

Othman Alshamrani
Department of Building Engineering, College of Architecture and Planning,
Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia

Abstract
Purpose – Buildings are responsible for the consumption of around 40% of energy in the world and account
for one-third of greenhouses gas emissions. In Saudi Arabia, residential buildings consume half of total energy
among other building sectors. This study aims to explore the impact of sixteen envelope variables on the
operational and embodied carbon of a typical Saudi house with over 20 years of operation.
Design/methodology/approach – A simulation approach has been adopted to examine the effects of
envelope variables including external wall type, roof type, glazing type, window to wall ratio (WWR) and
shading device. To model the building and define the envelope materials and quantify the annual energy
consumption, DesignBuilder software was used. Following modelling, operational carbon was calculated.
A “cradle-to-gate” approach was adopted to assess embodied carbon during the production of materials for the
envelope variables based on the Inventory of Carbon Energy database.
Findings – The results showed that operational carbon represented 90% of total life cycle carbon, whilst
embodied carbon accounted for 10%. The sensitivity analysis revealed that 25% WWR contributes to a
significant increase in operational carbon by 47.4%. Additionally, the efficient block wall with marble has a
major embodiment of carbon greater than the base case by 10.7%.
Research limitations/implications – This study is a contribution to the field of calculating the embodied
and operational carbon emissions of a residential unit. Besides, it provides an examination of the impact of each
envelope variable on both embodied and operational carbon. This study is limited by the impact of sixteen
envelope variables on the embodied as well as operational carbon.
Originality/value – This study is the first attempt on investigating the effects of envelop variables on carbon
footprint for residential buildings in Saudi Arabia.
Keywords Building envelope, Embodied carbon, Life cycle assessment, Operational energy
Paper type Research paper

1. Introduction
Buildings are associated with environmental impacts and are responsible for the significant
release of greenhouse gases (GHGs) (Alrashed and Asif, 2014; H€akkinen et al., 2015). The
building industry accounts for 19% of GHG emission in the world, and is considered a major
consumer of construction materials (Ching and Shapiro, 2014; Giesekam et al., 2016; Hollberg
and Ruth, 2016). Buildings generally demand two types of energy; operational energy (OE)
and embodied energy (EE) that both contribute to carbon footprint (Iddon and Firth, 2013;
Shreve and Shreve, 2018). Operational carbon accounted for the greatest amount of total
carbon footprint, whilst embodied carbon is emitted during materials harvesting, production,
International Journal of Building
Pathology and Adaptation
The authors would like to thank Imam Abdulrahman Bin Faisal University for the support and facilities © Emerald Publishing Limited
2398-4708
provided to carry out this research. DOI 10.1108/IJBPA-08-2020-0064
IJBPA transportation, construction and disposal, representing a lower carbon share (Ching and
Shapiro, 2014; Iddon and Firth, 2013; Monahan and Powell, 2011). In Saudi Arabia, the
building sector consumes almost 80% of total electricity at the national level during the
operational phase (Al-Ghamdi and Alshaibani, 2018; Asif et al., 2017). In 2017, Saudi
residential buildings consumed 49.6% of electrical energy (ECRA, 2017). Moreover, the
Electricity and Cogeneration Regularity Authority reported that 70% of electrical energy is
consumed during cooling as a result of the harsh climate (SEEC, 2018). Energy production in
Saudi Arabia depends on fossil fuels, further contributing to GHGs. Between 1990 and 2017,
carbon dioxide quantity in Saudi Arabia increased from 156 to 589 metric tons of CO2,
respectively (Al-Shaalan et al., 2014; Alamri, 2018; AlHashmi et al., 2017).
The life cycle assessment (LCA) is a quantitative approach that evaluates the
environmental impact of building materials and the processes (Asif et al., 2017; Saunders
et al., 2013). The whole LCA of any building includes all the evaluation for five building life
cycle stages. These stages are defined by the European Committee for Standardization EN:
15978, which are, A1-3 product stage, A4-5 construction process stage, B1-7 use stage, C1-4
end of life stage and D benefits and loads beyond the system boundary (Vilches et al., 2017).
A “cradle-to-gate” approach comprises energy and non-energy inputs including the raw
materials extraction and product manufacturing (Dixit, 2017).
The building envelope is the dominant element of a building that plays an essential role in
affecting operational energy. Thus, heat flow, air and moisture must be controlled effectively
(Allen and Iano, 2013; Azari et al., 2016; Azari and Kim, 2014; Granadeiro et al., 2013; Rivard
et al., 1998). The envelope must be designed to be responsive to the harsh hot climate by the
selection of materials, fenestration size and glazing type (Numan et al., 2001). The Saudi
Building Code National Committee developed the Saudi Energy Conservation Code for low-
rise (residential) buildings (SBC 602). This code indicates the minimum requirements for
exterior building envelopes that include insulations, U-values of windows and doors and
solar heat gain coefficient (SHGC) ratings (SBCNC, 2018).
Therefore, this study aims to contribute to the body of knowledge regarding a building’s
carbon footprint in harsh climate. It aims to explore the impact of sixteen envelope variables
that are compliant with SBC 602 requirements on the operational and embodied carbon over
20 years of a typical Saudi house in Riyadh. Accordingly, the main objectives of this study are
(1) to perform an energy simulation for quantifying the annual energy as well as the
operational carbon;
(2) to carry out measurements of embodied carbon of envelope materials;
(3) to examine the impact of each envelope variable on the carbon footprint.

2. Literature review
The environmental impact of embodied and operational energy has been studied extensively.
Internationally, the Hoxha (2019) study provided comprehensive measures of embodied
carbon emissions of two typical apartments in Kosovo in terms of construction materials. The
study indicates that the utilisation of steel, concrete and precast fabricated concrete plays an
essential role in the incensement of embodied carbon (Hoxha, 2019). Iddon and Firth (2013)
compared operational carbon and embodied carbon of a typical detached house in the UK.
The authors found that operational energy accounts for 74–80% of total carbon emissions
over 60 years. On the other hand, the cradle-to-gate embodied carbon accounted for 20–26%
(Iddon and Firth, 2013). Another study emphasised the combined assessment for operational
and embodied carbon of various insulation types of a typical semi-detached residential
building located in the UK. The additional insulation materials played a role in increasing
total carbon (Resalati et al., 2020). Furthermore, Azari (2014) examined six environmental Impact of
impacts based on envelope scenarios for a two-storey office building in Seattle, US. Four building
envelope components (which are insulation material, window to wall ratio (WWR), window
frame material and double-glazing cavity gas) were selected to create six envelope
envelope
combinations. This study affirmed that the building operational stage plays a vital role in systems
increasing environmental impact amongst all the stages. Furthermore, it is indicated that
envelope elements have a major influence on thermal performance of the indoor environment.
It has been recommended that future studies should perform a parametric analysis to explore
building envelope factors and how they affect environmental performance and energy use
(Azari, 2014). Similarly, in Canada, Alshamrani et al. (2014) developed a model that integrates
the LCA methodology with Leadership in Energy and Environmental Design (LEED) ratings.
The model aims to enable selection of a Canadian school’s envelope types and structural
systems in terms of sustainable design. Moreover, the model can be utilised during design for
assessing three main rating categories of the LEED system: LCA, energy and materials and
recourses. The authors achieved this by testing seven configurations of envelope elements,
including structural frame type, exterior wall type, floor type and roof type. The study
revealed that concrete and masonry buildings lead to energy consumption increases and
impacts the environment, such as global warming potentials during the manufacture phase
(Alshamrani et al., 2014). Another study examined in Hong Kong the effect of five building
envelope measures; exterior wall insulation, window overhang, exterior wall colour, WWR
and window glass type on the energy performance in a hot–humid climate. The results
revealed that building envelope design measures had a significant effect on building energy
use. Furthermore, cooling energy had decreased nearly to 46.81% with the application of
efficient envelope design measures. This included changing the window glass type which
mitigated the cooling load by as much as 20.26% (Sang et al., 2014). To further study the
environmental, social and economic impact of building façades, Saleem et al. (2018)
investigated the life cycle energy (LCE), LCA and life cycle costing (LCC) of four building
façade materials: brick, aluminium, granite and glass. A medium-rise commercial building
located in Belo Horizonte, Brazil, was selected as the location of choice. The granite façade
appeared to be the optimal sustainable alternative. Although the operational phase has major
impact on the environment, economics and society, the study identified air cavities between
the external and supported façade as a way of conserving energy during building of the
operational stage (Saleem et al., 2018). In the Middle East and North Africa (MENA) region, in
Jordan, Jaber and Ajib (2011) assessed the optimal residential building located in the
Mediterranean region in terms of energy efficiency. It was found that choosing the optimal
building orientation, optimum window size with the use of shading device and the optimum
thickness of thermal insulation contributes to saving the annual energy use by 27.59%;
furthermore, the LCC reduced by 11.94% (Jaber and Ajib, 2011). Locally, in Saudi Arabia, Asif
et al. (2017) examined the LCA of construction materials utilised in an existing three-bedroom
house located in Dhahran. The study focused on the embodied energy of 18 construction
materials of the house. A cradle-to-gate approach was adopted focussing on the construction
phase, where five environmental impacts were considered, including the global warming
potential (GWP). The study found that concrete accounts for 91% of the total construction
material and has the highest GWP compared to the other materials. The authors
recommended that future studies investigate environmental friendly construction
materials and techniques (Asif et al., 2017). Although the study conducted a
comprehensive life cycle assessment for building materials, operational carbon was not
considered. Another study aimed at improving the energy use intensity (EUI) of residential
buildings in Saudi Arabia, which focused on selecting the optimal design of the building
envelope based on the requirements of the Saudi Building Code for the energy conservation
requirements (SBC-601). This study conducted an energy simulation to calculate energy
IJBPA consumption throughout five climate zones in Saudi Arabia. Each simulation includes five
envelope parameters which are wall insulation, roof insulation, window area, window
glazing, window shading and thermal mass. Additionally, the study performed a cost
sensitivity analysis which pointed out that the energy cost has a lower impact on the initial
cost of the optimal envelope design associated with energy efficiency measures than the cost
of electricity rate and energy cost (Alaidroos and Krarti, 2015). This study has emphasised
energy use regardless of the environmental impacts associated with the embodied energy of
the envelope materials.
Table 1 is an inventory for previous studies that focused on the impact of building
envelope design on the environmental impact. The table shows which envelope parameter
was considered for each study as well as the measures that were performed.
According to previous studies, the building envelope is a major building element that has
an essential impact on both embodied and operational carbon. However, none of these studies
provided a holistic assessment of embodied and operational carbon emissions of a typical
residential building located in a harsh and hot climate such as Saudi Arabia. Furthermore, not
all the previous studies conducted a parametric study to examine envelope elements that
have the greatest amount of carbon emission. Thus, the present paper is a novel contribution
in the field of embodied and operational carbon emissions of a typical Saudi family house.
This study focuses on sixteen envelope variables compliant with the requirements of the
Saudi Building Code SBC 602.

3. Methodology
This study comprises two main quantitative methods: (1) energy simulation and (2)
calculation of operational and embodied carbon, as depicted in Figure 1. The study focuses on
16 envelope variables categorised under five inputs: (1) external wall type, (2) roof type, (3)
glazing type, (4) WWR and (5) shading device. Furthermore, a parametric study is conducted
to examine the impact of each building envelope variable on operational and embodied
carbon.

3.1 Base case model description

A typical Saudi family house represents the base case model for this study, as part of a large
housing project developed by the Ministry of Housing. The project contains 500,000 units
that are established or to be built among the cities in Saudi Arabia (Lasker, 2016). Each
residential unit measures a built-up area of 230 m2. The house consists of two floors and three
bedrooms (Figure 2; ground floor -A, and first floor -B) (Ministry of Housing, 2020).
The Saudi Building Code SBC 602 entitled Saudi Energy Conservation Code for a low-rise
residential building was produced by the Saudi Energy Efficiency Centre (SEEC) (SBCNC,
2018). The SBC 602 is based on the International Energy Conservation Code (IECC) and the
American Society of Heating Refrigerating and Air-Conditioning Engineers (ASHRAE)
(AlFaraidy and Azzam, 2019; Krarti et al., 2017). The code sets the minimum energy efficiency
requirements for low-rise residential units in Saudi Arabia. It indicates the minimum
requirements for building envelope insulation, fenestrations and doors U-factors, and the
solar heat gain coefficient (SHGC) ratings (SBCNC, 2018). Riyadh city (24.70N Latitude,
46.73E Longitude and 620 m above sea level) was chosen as the main location for the base
case model in this study, and it is categorised under climate zone 1 according to SBC 602. This
zone is an extremely hot region with a maximum dry bulb (DB) of 47.2 and has cooling degree
days (CDD) 10 around 6,107 (SBCNC, 2018). Table 2 demonstrates the requirements for zone 1,
including thermal performance for external wall assembly, roof assembly, glazing type,
WWR, infiltration rate and lighting power density (LPD). The characteristics of the base case
 Building’s Measures Impact of
envelope Number of building
Building type variable Description EE OE LCC scenarios References
envelope
Two-story office Wall type Insulation material U U 6 Azari (2014) systems
building Roof type Insulation material
Window to –
wall ratio
(WWR)
Glazing type Double-glazing cavity
gas
School building Wall type Structural frame type U U 7 Alshamrani
and exterior wall type et al. (2014)
Roof type –
High-rise Window to – U U 5 Sang et al.
residential tower wall ratio (2014)
(40 Floors) (WWR)
Wall type Exterior wall insulation
and exterior wall colour
Glazing type Window glass type
Shading Window overhang
device
medium-rise Wall type Four building facades U U U 4 Saleem et al.
commercial materials including (2018)
building brick, granite, aluminium
and glass
Residential Building – U U Jaber and Ajib
building orientation (2011)
Shading –
device
Window to Window size
wall ratio
(WWR)
Wall type Thermal insulation
thickness
Roof type Thermal insulation
thickness
Residential Wall type Wall insulation and U U One scenario Alaidroos and
building thermal mass for 5 different Krarti (2015)
Roof type Roof insulation and climate zone
thermal mass
Glazing type Window glazing
Shading Window shading
device Table 1.
Window to Window area Building’s envelope
wall ratio environmental impact
(WWR) from previous studies

Figure 1.
Overview research
approach
IJBPA

Figure 2.
Typical Saudi family
house floor plans
(Ministry of
Housing, 2020)

Wall assembly Maximum: U- 0.342 W/m2. k

Roof assembly Maximum: U- 0.202 W/m2. k
SRI (Solar Reflectance Index) Light colour
SRI ≥ 50
Glazing Maximum: U- 2.66 W/m2. k
Double glazing
SHGC ≤ 0.25
Window to wall ratio 0–25%
External shading devices Overhanded 30 cm
Door Maximum: U- 2.839 W/m2. k
Infiltration rate for fenestration 1.5 L/s/m2, 0.75 ach
Indoor conditions
Table 2. DB: Dry bulb Summer: DB 23.98 RH: 50%
SBC 602 residential RH: Relative humidity Winter: DB 21.18 RH: 30%
building requirements Lighting power density (LPD) 10 Watts/m2
for Zone 1 Note(s): SBCNC (2018)

model of the typical Saudi house are in compliance with the minimum requirements of SBC
602, (Table 3) (Hamida et al., 2020). The weather file that is used in this study is Riyadh 404380
(IWEC) that is generated by The International Weather for Energy Calculations (IWEC)
datasets which are a converted format suitable for EnergyPlus (EPW).

3.2 Choices of building envelope

The building cooling load in Riyadh consumes 70% of total electrical energy consumption in
Saudi Arabia (AlFaraidy and Azzam, 2019). The cooling load directly relies on electrical
energy that is generated through burning fossil fuels, leading to the increase energy use
intensity (EUI). Generally, building components that contribute to high usage of cooling load
in Saudi houses are the roof, walls and glass (Numan et al., 1999). Therefore, five envelope
parameters were selected for this study; exterior walls, roof, glazing type, WWR and shading
Weather file SAU_Riyadh.404380_IWEC Impact of
Orientation The front elevation facing the East building
Geometry Stories number 2
Gross built area 375 m2 envelope
Gross floor area 230 m2 systems
Ground floor area 194 m2
First floor area 90 m2
Plan proportion 6:7
Total building height 6.7 m
Gross wall area 318 m2
Glazing area 15 m2
WWR 5%
External wall construction Layers 15 mm cement plaster
(Base wall) 100 mm concrete block
90 polystyrene
100 mm concrete block
15 mm cement plaster
U-value 0.34 w/m2. k
Roof construction (Base roof) Layers (outside to 20 mm Ceramic tile
inside) 20 mm mortar
10 mm sand
100 mm polyurethane
4 mm bitumen felt
200 mm concrete slab
15 mm cement plaster
U-value 0.21 w/m2. k
Floor construction Layers (top to bottom) Ceramic tiles
Mortar
Sandstone
Reinforced concrete
Asphalt Insulation
Concrete high density
Base-course stone
Earth
U-value 2.02 w/m2. k
Glazing type (Base glazing) Double clear glazing (6 mm glass, 12 mm air gap, 6 mm glass)
U-value 2.6 w/m2. k
Air leakage 1.5 L/s/m2, 0.75 ach
External shading Horizontal panel projected 30 cm
devices
Occupants Numbers Total: 6 (2 adults and 4 children)
Density 0.0211 person/m2
Schedule Residential: weekdays (Sunday to Thursday): Unoccupied
from 8 a.m. to 4 p.m.
Lighting Lighting display 7.3 kW/m2
density
Target illuminance 150 lux
HVAC system Package terminal air conditioner (DX system) CoP: 2.5
Heating 21.18C
Heating setback 18.18C
Cooling 23.98C
Cooling setback 27.98C Table 3.
Humidification setpoint 30% Characteristics and
Dehumidification 50% specifications of
setpoint typical Saudi
Source(s): Hamida et al. (2020) family house

devices. These were chosen due to their importance in increasing the building’s operational
energy and the environmental impacts.
(1) External wall
IJBPA Currently, a wide range of insulation materials are applied in the building sector such as
polyurethane, polystyrene and rock wool. Polyurethane is an optimum insulator as it has a
highly efficient thermal performance and is cost effective (AlFaraidy and Azzam, 2019).
A previous study based in Saudi Arabia revealed that the application of polystyrene
insulation led to the reduction of electrical energy up to 10% (Numan et al., 1999). Hence, the
selected wall variables include both insulators, polyurethane and polystyrene. Table 4 lists
the thermal and physical features of the four exterior wall variables. All external wall
variables are compliant with required thermal transmittance of SBC 602. All include a
continuous thermal insulation, mandatory to all external walls above grade in residential
buildings.
(2) Roof type
The building roof is directly exposed to solar heat, resulting in an increased cooling demand
(Algarni, 2019). The SBC 602 states that the roof assembly must include thermal insulation.
Table 5 demonstrates the thermal and physical features of three roof variables.
(3) Glazing type
Fenestrations are considered a significant factor for increasing heat gain. However, the use of
high performance glazing type such as double-glazed low-E windows contribute to reducing
the energy consumed for cooling loads (Abdul and Budaiwi, 2015). Table 6 illustrates the four
glazing variables that are double glazed with an air cavity.
(4) Window to wall ratio (WWR)
The WWR for zone 1 must not exceed 25% of the wall (SBCNC, 2018). Hence, the three WWR
variables are 25%, 20% and 10% (Table 7).
(5) Shading devices
The shading devices used are overhangs, side fins and louvres. All are effective elements that
contribute to mitigating the cooling energy, particularly during summer (Alaidroos and
Krarti, 2015; Kirimtat et al., 2016). Table 8 includes the two variables of external shading
devices.

3.3 Description of envelope scenarios

In Figure 3,16 scenarios of envelope combinations are presented . In each scenario, only a
single envelope variable is modified, whilst the other building parameters are controlled,
according to the base case model characteristic. For instance, “WALL 1” scenario has the
same characteristics of base case model, except the wall type, which is changed to “Wall 1:
Thermal block wall”.

3.4 Embodied and operational carbon calculations

The LCA method is partially applied in this study to quantify both embodied and operational
carbon. Hence, the aim of the LCA is to compare the amount of embodied and operational carbon
amongst the 16 envelope scenarios. The functional unit is measured in kgCO2 =m2 for both
embodied and operational carbon. The building life span is determined according to the
Demography Survey 2016 issued by the General Authority for Statistics. The majority of houses in
Riyadh city are around 20 years old (General Authority for Statistics, 2016). The system boundary
is limited to the product stage (A3: manufacturing) and the use stage (B6: operational energy use).
(1) Operational carbon
DesignBuilder is a simulation tool with a graphical user interface (GUI) and uses EnergyPlus
as a dynamic simulation engine for energy calculations of comprehensive dynamic
 Impact of
Wall Type U-factor Section building
Layers from outside to inside W/ m2. k
Wall 1. Thermal block wall
envelope
0.20 20 mm cement plaster
systems
Layers:
(1) 12 mm plaster 75 mm concrete block

(2) 75 mm Concrete block

(3) 160 mm Expanded polystyrene
(4) 75 mm Concrete block 160 mm Expanded polystyrene insulation
(5) 12 mm plaster

75 mm concrete block

20 mm cement plaster

Wall 2. Efficient block wall with marble

0.24
50 mm marble
Layers:
25 mm mortar
(1) 50 mm Marble
(2) 25 mm Mortar 50 mm concrete block
(3) 50 mm Concrete block
(4) 50 mm polyurethane board 50 mm Expanded polystyrene insulation
(5) 200 mm Concrete block

200 mm concrete block

20 mm cement plaster

Wall 3. Thermal block wall

0.31 12 mm cement plaster
Layers:
(1) 12 mm plaster 100 mm concrete block

(2) 100 mm Concrete block

(3) 70 mm polyurethane
(4) 150 mm Concrete block 70 mm Foam polyurthane

(5) 12 mm plaster

150 mm concrete block

12 mm cement plaster

Wall 4. External Insulation and Finish

System 0.33 12 mm cement plaster

Layers: 70 mm Foam polyurthane

(1) 12 mm Plaster
(2) 70 mm polyurethane
(3) 150 mm concrete block
(4) 12 mm plaster 150 mm concrete block

12 mm cement plaster Table 4.

External wall variables
IJBPA
Roof Type U-factor Section
Layers from outside to inside W/ m2. k
Roof 1. Green Roof 0.19
Vegetation layer
1 mm Slab-Filter layer
Layers: 1 mm polypropylene fiber
8 mm water drainage/ storage elements (DAKU FSD)
(1) Vegetation layer 50 mm Expanded polystyrene insulation
(2) 1 mm Slab-Filter layer 4 mm Bitumen layer

(3) 1 mm polypropylene fibre

(4) 1250*100*80 mm water drainage/
storage elements 300 mm concrete ribbed slab

(5) 4 mm Anti-Root & Rot

waterproofing membrane
(6) 50 mm Expanded polystyrene
10 mm cement plaster
insulation
(7) 4 mm Bitumen layer
(8) 300 mm concrete ribbed slab
(9) 10 mm ceiling plaster
Roof 2. Siporex light concrete Tiles 0.18
20 mm Ceramic tile
20 mm Mortar
Layers: 25mm Sand
(1) 50 mm Tiles+ Mortar 4 mm waterproof membrane
50 mm Expanded polystyrene insulation
(2) 25mm Sand,
(3) 4 mm waterproof membrane 100 mm Foam Concrete

(4) 50 mm Expanded Polystyrene

(5) 100 mm Foam Concrete
(6) 200 mm Siporex slab panel 200 mm Siporex

(7) 15 mm Cement plaster

15 mm cement plaster

Roof 3. Reinforced Concrete Insulated 0.20

slab 20 mm Terrazzo
20 mm Mortar
25mm Sand
4 mm waterproof membrane
Layers: 4 mm Polyurethane
(1) 20mm Terrazzo
100 mm Foam Polyurethane
(2) 20 mm Mortar
(3) 25 mm Sand
(4) 4 mm waterproof membrane 200 mm Reinforced Concrete
(5) 100 mm polyurethane
(6) 200 mm RC slab
Table 5. (7) 15 mm cement plaster 15 mm cement plaster

Roof type variables

parameters (Abdul and Budaiwi, 2015; AlHashmi et al., 2017). It enables the user to quantify
building energy performance data using advanced tools for 3-D modelling (DesignBuilder,
2019a; IBPSA-USA, 2019). A field visit to a Saudi house under construction, part of the
housing project developed by the Ministry of Housing, was undertaken. The aim was to
compare the actual amount of energy consumption taken from an electrical bill with the
output of the annual energy consumption generated by DesignBuilder. This field visit
included an exploration of the main envelope materials; exterior wall assemblies, roof
assemblies and glazing type (Plate 1). According to the Demography Survey 2016 issued by
the General Authority for Statistics, the age of 32% of Saudi houses in Riyadh City is around
20 years, which represents the greatest portion among other approximate house ages
 Impact of
Roof Type U-factor SHGC Section building
Layers from outside to inside W/ m2. k (solar heat envelope
gain
coefficient)
systems
Glaz 1. Doubled low-e glazing
6 mm low-e glass, 12 air, 6 mm low-e glass 1.65 0.634

6 12 6
Glaz 2. Doubled bronze tint glazing 0.38
(DTG) 2.61
6 mm tint glass, 13 mm air, 6 mm tint glass
6 13 6
Glaz 3. Doubled low-e clear glazing 0.568
6 mm clear glass, 12 mm argon gas, 6 mm 1.52
clear glass
6 12 6
Glaz 4. Doubled low-e tint glazing 1.16 0.373
6 mm tint glass, 12 mm argon gas, 3 mm
tint glass Table 6.
6 12 6 Glazing type variables

Table 7.
Window to wall ratio
(WWR) variables

(General Authority for Statistics, 2016). In addition, the King Abdullah Petroleum Studies and
Research Centre (KAPSARC) report pointed out that carbon emissions factor for electrical
energy production in Saudi Arabia is 0.757 kgCO2 per kWh (Krarti et al., 2017). Hence, the
method of calculation is defined in equation (1) for quantifying operational carbon resulting
from the cooling load over 20 years of the base case model. The annual cooling load is
obtained by the run of energy simulation in DesignBuilder.
OCCO2 ¼ OE 3CF 3A (1)

Where,
OCCO2 5 Operational carbon emissions (kgCO2), resultant from the cooling load;
OE 5 Operational Energy (kWh);
variables
IJBPA

Table 8.
Shading device
Shading Device SD 1. Overhang \vertical side fins shading device SD 2. Louvers shading device
Direction Overhang applied for South elevation Applied for all elevations except north
Vertical side fins applied for East and West
elevations
Specifications 50 cm projection 15 cm projection from window, 5 blades, 35 cm
vertical spacing, 300 angles, 25 cm blade depth
WWR 5% 5%
Illustration Horizontal window
overlap
Overhang Vertical offset from top of Vertical offset from
Projection window top of window Louvre blades
Horizontal offset from
window left Horizontal offset vertical spacing
from window right

Win
Window Louvre blades
Blade depth
Window

Angle Horizontal window Window

overlap
Distance from
window
Left Sidefin Front Elevation
Right Sidefin
Projection Side Elevation
 Impact of
building
envelope
systems

Figure 3.
Envelope design
scenarios

Plate 1.
Existing materials for
the building envelope
assemblies of the base
case model

CF 5 Carbon Factor 5 0.757 kgCO2/kWh;

A 5 Approximate age 5 20 years.

(2) Embodied carbon

DesignBuilder provides a calculation for embodied carbon emissions of building materials
(AlHashmi et al., 2017). It estimates embodied and equivalent carbon data obtained from the
IJBPA Inventory of Carbon Energy (ICE) database (DesignBuilder, 2019b). The ICE database was
developed by the Sustainable Energy Research Team at the University of Bath (University of
Bath, 2020; Kumanayake and Luo, 2017). This database provides equivalent carbon (kgCO2)
as embodied carbon and includes the impact of other greenhouse gases, such as sulphur
dioxide and methane, emitted during processes involved in production of the material
(DesignBuilder, 2019b). The first LCA study of a Saudi residential building indicated that
there is an absence of the local databases. Accordingly the study adopted the use of
international databases for calculating the embodied energy as well as the environmental
impacts (Asif et al., 2017). Hence, due to the lack of a comprehensive Saudi database, data
from ICE database are utilised in this study.

4. Result
4.1 Operational carbon
Field visit data were used to define the characteristics of an existing Saudi house developed
by the Ministry of Housing. Accordingly, an energy simulation was performed for the
existing building. Figure 4 illustrates the 3D model of the existing house in DesignBuilder to
quantify monthly energy consumption. The calibration approach of the simulation model
was done by comparing the model monthly usage predictions in DesignBuilder to monthly
utility bill data. An electricity consumption bill was also obtained from the owner of one of the
houses located in Majmaah city, Riyadh region. The difference between actual consumption
of utility bill and building energy modelling over the 12 months over are demonstrated in
Figure 5. Energy consumption results were mostly similar between the actual results and
simulation results. The relative change between the measured and predicted overall energy
consumption was found to be 11%. However, in October and November the actual energy
consumption was higher than energy generated by DesignBuilder. Also, in April, May and

Figure 4.
Existing house model
in “DesignBuilder”
 Impact of
building
envelope
systems

Figure 5.
Calibration of the
simulation results

June, the actual energy was significantly lower than the energy simulation results. These
months were excepted due to occupant behaviour; where the homeowner indicated that the
building was unoccupied during the end of April, May and the start of June. Accordingly, the
differences in energy consumption between utility bill and energy simulation during July,
August, September, December, January, February and March were almost identical were the
relative change was 4%.
Seventeen energy simulations and calculations for embodied and operational carbon were
performed for 16 envelope scenarios and the base case model. Table 9 displays results for the
annual energy consumption and the operational energy for the base case model and
scenarios.

Operational energy (kWh) Operational carbon (kgCO2)

Base 16,865 255,336

WALL 1 16,230 245,722
WALL 2 15,852 239,999
WALL 3 16,530 250,264
WALL 4 17,530 265,404
ROOF 1 16,707 252,944
ROOF 2 16,710 252,989
ROOF 3 16,831 254,821
GLAZ 1 16,172 244,844
GLAZ 2 16,501 249,825
GLAZ 3 16,236 245,813
GLAZ 4 15,986 242,028
WWR 10% 18,188 275,366
WWR 20% 22,653 342,966 Table 9.
WWR 25% 24,856 376,320 Operational energy
SD 1 16,604 251,385 and operational carbon
SD 2 16,287 246,585 results
IJBPA 4.2 Embodied carbon
The detailed results of the embodied carbon of the building materials for the base case model
of the typical Saudi house are demonstrated in Table 10. Table 11 further demonstrates
embodied carbon results for the envelope elements including the external wall, roof and
glazing. In terms of building materials, concrete block was found to be the largest share of
embodied carbon of 23.65%. On the other hand, in terms of envelope element, the roof
contributes to the largest ratio of embodied carbon of 42.19%.

5. Discussion
5.1 Comparison of operational and embodied carbon results
Our results show that over 20 years, the operational carbon was a major factor contributing to
total life cycle carbon (Figure 6). The “WWR 25%” scenario represents the greatest

Percentage of
Materials embodied Area Mass Embodied Equivalent CO2 material to overall
carbon and inventory (m2) (kg) carbon (kgCO2) (kgCO2) total

Foam – polyurethane 147.9 399.2 1197.7 1197.7 3.87%

Concrete roofing slab 147.9 14786.0 4879.4 5027.2 16.25%
aerated
Urethane/polyurethane 6.6 0.9 2.6 2.6 0.01%
(thermal break)
Clay tile (roofing) 147.9 7393.0 3400.8 3548.6 11.47%
Granite 147.9 5766.9 2249.1 2422.1 7.83%
Plaster (dense) 653.3 12739.5 1528.7 1656.1 5.35%
Aluminium 13.2 11.0 94.5 101.6 0.33%
EPS expanded 326.7 441.0 1102.5 1437.6 4.65%
polystyrene (standard)
Mortar 295.7 18630.9 3539.9 3539.9 11.44%
Concrete block 653.3 91462.8 7317.0 7317.0 23.65%
(medium)
Cast concrete 147.9 11622.4 929.8 929.8 3.00%
Cast concrete (dense) 88.2 18529.4 1482.3 1482.3 4.79%
Table 10. Bitumen/felt layers 147.9 1005.4 1709.3 1709.3 5.52%
Envelope materials Double clear glazing 15.9 572.4 572.4 1.85%
embodied carbon Sub Total 30944.3 30005.8 30944.3 100%

Constructions embodied Area Embodied carbon Equivalent CO2 Percentage of element

carbon and inventory (m2) (kgCO2) (kgCO2) to overall total

Exterior door 6.6 97.0 104.2 0.34%

External wall base model 326.7 9948.2 10410.8 33.64%
Base building roof 147.9 12760.3 13056.0 42.19%
Project internal floor 88.2 1482.3 1482.3 4.79%
Ground floor 147.9 5145.5 5318.5 17.19%
Sub total 717.2 29433.42 30371.86 98.15%
Glazing embodied carbon and inventory
Table 11. Base model glazing 15.9 572.4 572.4 1.85%
Envelope elements Sub total 15.9 572.4 572.4 1.85%
embodied carbon Building total 733.1 30005.8 30944.3 100%
 Impact of
building
envelope
systems

Figure 6.
Results of operational
and embodied carbon
for the base case model
and the 16 envelope
scenarios

operational carbon emission of 1568 kgCO2/m2, while “WALL 2” shares the greatest
embodied carbon emission of 143 kgCO2/m2. In addition, the results demonstrate that
operational carbon accounts for the greatest proportion of 90% of total life cycle carbon, while
the embodied carbon is responsible for only 10% (Figure 7). Compared to the previous study
conducted by Iddon and Firth (2013), cradle-to-gate embodied carbon accounted for 22.3%,
while operational energy accounts for 77.7% of total carbon emissions over 60 years for a
UK house.
Moreover, in this study, the embodied carbon comprises the ratio of embodied carbon
within building envelope elements: the roof, external wall and glazing. The roof is a major
contributor of embodied carbon by 53%, followed by the exterior wall accounting for 44%.
The glazing is the lowest element in embodied carbon, accounting for 3%. Compared to a
previous study by Iddon and Firth (2013), the roof was the least parameter that contributes to
the embodied carbon, while the external walls and openings were the major elements that are

Figure 7.
(A) Proportion of the
average total
operational carbon and
embodied carbon (B)
Proportion of the
average total embodied
carbon for the building
envelope elements for
the 16 scenarios
IJBPA contributors to embodied carbon for a UK house (Iddon and Firth, 2013). Furthermore, in this
study roof and external wall variables consist of concrete, which is indicated from a previous
study by Asif et al. (2017) as a major material that shares the highest amount of embodied
energy among the building materials by 43.4% of a three-bedroom house in Saudi Arabia
(Asif et al., 2017).

5.2 Sensitivity analysis

Sensitivity analysis is a method that is necessary to evaluate the design parameters based on
their impacts on building performance (Østerg ard et al., 2017). Accordingly, sensitivity
analysis was utilised in this study to explore the impact of each envelope variable on both
operational and embodied carbon of the residential unit. This was run in comparing the
performance of the base case model with each sixteen envelope scenarios. This analysis
enables the prediction of how each envelope variable affects the model regarding embodied
and operational carbon. To this aim, two sensitivity analyses were carried out by controlling
the characteristics of the Saudi base house specified in Table 3. One independent variable was
changed through 16 combinations for each analysis. Each of these combinations was
compared with the base case model results.
Figure 8 demonstrates the impact of how each independent variable on carbon emissions
results from operational energy (cooling load). The WWR variables play a vital role in
increasing the operational carbon resulted from the cooling load. Additionally, the “WWR
25%” is the most significant variable, which increases these dependent variables by nearly
50%. It was noted that from a previous study by Azari (2014) that low to medium WWR leads
to mitigate the environmental impacts including the global warming potential (carbon
emissions) (Azari, 2014).
On the other hand, the exterior wall (WALL 2) and glazing type (GLAZ 4) mitigate the
operational carbon. All glazing types, roof, most of the exterior wall variables and shading
device variables decreased the operational carbon over 20 years of operation.
Figure 9 illustrates the effect of independent variables on the embodied carbon caused
during the production of the building envelope materials. WALL 2 and WALL 3 increase
embodied carbon by 11% and 6%, respectively. WALL 1 and WALL 4 mitigate embodied
carbon by 18% and 12%, respectively. Besides, roof types ROOF 1, ROOF 2 and ROOF 3 were
involved in reducing the amount of embodied energy by 11%, 18% and 6%, respectively.
However, all the glazing types, WWR and shading device variables were ineffective on the
embodied carbon.

Figure 8.
Impact of envelope
variables on
operational carbon
compared to base
case model
 Impact of
building
envelope
systems

Figure 9.
Impact of envelope
variables embodied
carbon compared to the
base case model

6. Conclusion
This study evaluated the impact of sixteen envelope variables on the life cycle of operational
and embodied carbon of a typical Saudi family house with 20 years of operation. Our results
revealed that operational carbon is the major contributor to life cycle carbon that shares 90%
of the total carbon, while embodied carbon represents 10% of carbon footprint. A sensitivity
analysis revealed that 25% of the WWR parameter contributed to the greatest amount of
operational carbon by 47.4%, compared to the base case model. Thus, the minimum WWR
has a significant role in mitigating the total carbon emissions. On the other hand, the efficient
block wall with marble (WALL 2) shares the greatest amount of embodied carbon, more than
the base case by 10.7%. However, this wall type has the potential for saving around a 6%
carbon footprint resulted from operational energy. Additionally, the findings of this study
affirmed that concrete block contains the predominant ratio of embodied carbon amongst
other envelope materials. Besides, the roof assembly shares the largest proportion of
embodied carbon, followed by the external wall assembly. This study provided an insight
into the significant relation between the envelop variables and the carbon footprint in the
residential buildings in Saudi Arabia.
For further studies, it is essential to develop a model that quantifies operational and
embodied carbon at the early design stage, to minimise both outputs. Additionally, carbon
emissions derived from other life cycle stages of a typical Saudi house could be investigated.
This includes the construction and end of life stages, which were not considered in this study.
Other building systems that were not included in this paper, such as lighting, cooling and
heating could be considered for future research to study their impact on carbon emissions.

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Corresponding author
Amneh Hamida can be contacted at: amneh.hamida@gmail.com

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