CHEMICAL ENGINEERINGTRANSACTIONS
VOL. 52, 2016
A publication of
The Italian Association
of Chemical Engineering
Online at www.aidic.it/cet
Guest Editors:Petar Sabev Varbanov, Peng-Yen Liew, Jun-Yow Yong, Jiří Jaromír Klemeš, Hon Loong Lam
Copyright © 2016, AIDIC Servizi S.r.l.,
ISBN978-88-95608-42-6; ISSN 2283-9216
Comparison of Material Compositions of Roofs in term of
Environmental and Energy Performance
Eva Kridlova Burdovaa, Silvia Vilcekova*a, Jaroslav Vojtusb, Anna Sedlakovab
a
Institute of Environmental Engineering, Faculty of Civil Engineering,Technical University of Košice, Vysokoškolská 4, 042
00 Košice, Slovakia
b
Institute of Architectural Ingineering, Faculty of Civil Engineering,Technical University of Košice, Vysokoškolská 4, 042 00
Košice, Slovakia
silvia.vilcekova@tuke.sk
In world with limited amount of energy sources and with serious environmental pollution, interest in comparing
the environmental embodied impacts of buildings using different structure systems and alternative building
materials will be increased. The selection of building materials used in the constructions (floors, walls, roofs,
windows, doors, etc.) belongs to one of the most important roles in the phase of building design. This decision
has impact on the performance of building with respect to criteria of sustainability. The energy used in
extraction, processing and transportation of materials used in building constructions can be significant part of
the total energy used over the life cycle of building, particularly in nearly-zero energy buildings. The
environmental impacts are expressed by indicators such as embodied energy (EE) from non-renewable
resources, embodied CO2.eq emissions (GWP, Global Warming Potential) and embodied SO2eq emissions (AP,
Acidification Potential) within system boundary from Cradle to Gate. The aim of analysis is to identify the
environmental quality of material compositions for designed variants of roof constructions. The final values of
assessments are compared by using methods of multi-criteria decision analysis.
1. Introduction
Directives in the European Union are ensuring that buildings in this region are moving towards nearly zero
energy buildings (nZEB) (Goggins et al., 2016). The construction industry in general and buildings in particular
are key drivers of natural resource consumption and emissions into the environment, aside from their effects
on the economy and society. Considering these effects that occur throughout a building’s whole life cycle,
including but not limited to production of construction materials, demolition of building and waste disposal,
various assessment methods and tools are being developed to account for the different aspects of
sustainability (Ceniter, 2014). Construction has been accused of causing environmental problems ranging
from excessive consumption of global resources both in terms of construction and building operation to the
pollution of the surrounding environment, and research on green building design and using building materials
to minimize environmental impact is already underway. However, relying on the design of a project to achieve
the goal of sustainable development, or to minimize impacts through appropriate management on site, is not
sufficient to handle the current problem. The aim for sustainability assessment goes even further than at the
design stage of a project to consider its importance at an early stage, before any detailed design or even
before a commitment is made to go ahead with a development. However, little or no concern has been given
to the importance of selecting more environmentally friendly designs during the project appraisal stage; the
stage when environmental matters are best incorporated (Ding, 2008). During the last few decades there has
been an increasing interest in environmental assessments of the built environment. As a result, we can find
several qualitative and quantitative assessment tools (Forsber et al., 2004). In the life cycle of a building,
various natural resources are consumed, including energy resources, water, land, and minerals. Many kinds of
pollutants are also released back into the global or regional environment. These environmental inputs and
outputs result in global warming, acidification, air pollution etc., which inflict damage on human health, primary
production, natural resources and biodiversity. The building sector, constituting 30–40 % of the society's total
DOI: 10.3303/CET1652210
Please cite this article as: Kridlova Burdova E., Vilcekova S., Vojtus J., Sedlakova A., 2016, Comparison of material compositions of roofs in
term of environmental and energy performance, Chemical Engineering Transactions, 52, 1255-1260 DOI:10.3303/CET1652210
1255
energy demand and approximately 44 % of the total material use as well as roughly 1/3 of the total CO2
emissions (Erlandsson et al., 2003), has been identified as one of the main factors in greenhouse gas
emissions. There is no doubt that reducing the environmental burden of the construction industry is essential
to sustainable development (Li, 2006). In recent years, the desire to quantify the environmental impact of
human activities has increased more and more in order to help mitigate climate change. Various
environmental certification systems are being established such as the Environmental Product Declaration
(EPD) and thanks to this trend, the quantifiable impact, such as carbon footprint or energy demand can, for
instance, be seen on a product's label and in advertisements in daily life. This raises our awareness about
environmental problems and leads competition in industry. Life cycle assessment (LCA) is an internationally
recognized and ISO standardized accounting tool to quantify the environmental impacts of a product, a
process or a service throughout its life cycle, by identifying, quantifying and evaluating all the resources
consumed and all the emissions and wastes released in an analysis known as a "from cradle to grave"
(Iannone et al., 2014). LCA studies the potential environmental impacts throughout a product’s or system’s life
(i.e. from cradle to grave), from raw material acquisition through production. In the life cycle impact
assessment (LCIA) stage, an assessment is made of the potential human, ecological, and depletion effects of
energy, water, and material usage; and the environmental releases identified in the inventory. The impact
assessment is where the potential effects on the chosen environmental issues are assessed (Adams et al.,
2014). LCA supports industry and policymakers in making reasonable decisions concerning products,
processes and policy strategies. Since LCA is a data-intensive method, the availability of adequate and
reliable data is a fundamental issue for the assessment (Peeredoom, 1999). According to study (Frischknecht
et al., 2006) the ideally complete LCA database not only includes all datasets, but at the same time should
include the links in between them according to economic interrelations. This would result in a huge number of
interlinked datasets and an even larger number of links (inputs and outputs). Takano et al. (2014) investigates
numerical and methodological differences in existing databases related to building LCAs. They state that the
databases show similar trends in the assessment results and the same order of magnitude differences
between the reference buildings are shown by all the databases. In study (Rocha et al., 2014) the LCA is used
for the evaluation and comparison of main environmental life cycle impacts and energy balance of ethanol. In
another study (Iannone et al., 2014) the LCA was carried out to compare the environmental impacts and the
energy efficiency of four kinds of wines.
The aim of many papers is to analyse how to improve energy efficiency of buildings. Study of Hannoudi et al.
(2015) investigated façade system for existing office buildings in Copenhagen. Another study (Lupíšek et al.,
2015) is focused on design strategy for low embodied carbon and low embodied energy buildings. Study of
Sedláková et al. (2014) is focused on evaluation of structures design concept of lower structure from
embodied energy and emissions. Comparison of environmental and energy performance of exterior walls is
presented in another study (Vilčeková et al., 2015a). Salcido et. al. (2016) compares alternative materials
used in reticulated dome construction from embodied energy and environmental impact. Castell et al. (2013)
analyse the environmental impact of alveolar brick construction systems with and without phase change
materials. Buildings are major consumers of energy. Types of energy used during a building’s life cycle
comprise embodied energy, operational and maintenance energy, demolition and disposal energy. Embodied
energy (EE) represents the total energy consumption for a building construction, i.e., sum of embodied energy
of building materials, transportation energy of materials and building construction energy. Praseeda et al.
(2016) points out that EE of building materials represents major contribution to embodied energy in buildings.
The construction industry has significant environmental, social and economic impacts on the society. As a
result, the last decades have witnessed the rapid growth of the green building sector in order to mitigate the
negative impacts associated with construction related activities. Similar to conventional building projects,
green building projects have a variety of objectives that may not necessary be compatible. These include
upfront cost vs. ongoing savings; and energy savings vs. building users' health and wellbeing (Shi, 2016).
Zhang et al. (2015) proposes a detailed carbon emission inventory for buildings and divides the life-cycle of a
typical building into three stages based on material and energy flow: the materialization stage, the operation
stage, and the disposal stage. This study provides a standard method for life-cycle carbon assessment of
buildings, which will be critical for future low-carbon development. As study (Gardezi et al., 2016) states the
housing sector holds a very pivotal role in providing basic living needs and this role becomes more crucial with
an increase in population and rapid urbanization in any country.
Comparison of material compositions of variants of roof constructions is the main goal of this paper. Presented
alternatives of roof constructions are analysed from environmental quality and energy aspects. Methods of
multi-criteria decision analysis are used for investigation.
1256
2. Materials and methods
Three variants of roof constructions were designed to optimally economical and structurally accurate detail.
These variants were designed to meet the recommended value of heat transfer coefficient U = 0.10W/m.K.
Evaluated roof constructions are illustrated in Figure 1. Variant 1 consists of reinforced concrete slab, gravity layer,
vapour barrier, thermal insulation from EPS, separating layer, waterproofing from PVC and ceramic paving. Roof 2
consists of reinforced concrete slab, gravity layer, separating layer, waterproofing, from PVC, thermal insulation
from XPS, gravel and ceramic paving. And finally Roof 3 consists of reinforced concrete slab, gravity layer,
separating layer, thermal insulation from XPS, separating layers, gravel and vegetation layer.
Firstly, the variants are evaluated in terms of energy performance. Thermo-physical parameters are calculated for
Slovak climatic conditions (STN EN 730540): θe- outdoor air temperature (-13 °C); θi- indoor air temperature
(20 °C); Rh- relative air humidity outdoors (84 %) and Rh- relative air humidity indoors (50 %).
(a) Variant 1 (b) Variant 2 (c) Variant 3
Figure 1: Roof constructions
Table 1: Compositions of roofs and thermo-physical parameters
No. Assemblies Thickness
d[m]
Thermal
coefficient
λ [W/(mK)]
Specific heat
capacity
C [J/kg.K]
Density
ρ [kg/m3]
μ [-]
1 Reinforced concrete slab 180 1.58 1,020 2,400 29
Gravity layer - perlite
Vapour barrier - bitumen
Thermal insulation - EPS
Separating layer - geotextile
Waterproofing - PVC
Paving mat
Ceramic paving
50
1.5
350
1.5
1.5
25
30
0.13
0.21
0.037
0.16
1,150
1,470
1,270
960
450
1,140
20
1,400
11
300,000
70
16,700
2 Reinforced concrete slab
Gravity layer - perlite
Separating layer - geotextile
Waterproofing - PVC
Thermal insulation layer - XPS
Fine gravel
Ceramic paving
180
50
1.5
1.5
350
50
30
1.58
0.13
0.16
0.034
0.65
1.01
1,020
1,150
960
2,060
800
840
2,400
450
1,400
30
1,650
2,000
29
11
16,700
100
15
200
3 Reinforced concrete slab 180 1.580 1,020 2,400 29
Gravity layer - perlite
Separating layer - geotextile
Vapour barrier - bitumen
Separating layer - geotextile
Thermal insulation - XPS
Separating layer - geotextile
Gravel
Separating layer - geotextile
Vegetation layer
50
1.5
1.5
1.5
350
1.5
50
1.5
100
0.13
0.16
0.034
0.65
2.3
1,150
960
2,060
800
920
450
1,400
30
1,650
2,000
11
16,700
100
15
2
Material compositions of roof assemblies are evaluated from environmental and thermo-physical indicators.
Environmental indicators are calculated by LCA method. The results of assessment are compared through
mathematical method such as Concordance Discordance Analysis (CDA), Ideal Point’s Analysis (IPA), Weighted
1257
Sum Approach (WSA) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) (Vilcekova et
al., 2015a).
3. Results and discussion
Thermal-physical parameters for evaluated alternatives are presented in Table 2.
Table 2: Thermal-physical parameters of roof constructions
Variant d [mm] U [W/m2.K] R [m2.K/W] θsi [°C] fRsi,p [-] ν [1] Ψ [h]
1 641 0.099 9.98 19.20 0.976 732.9 13.10
2 663 0.091 10.91 19.26 0.978 1,727.9 19.60
3 737.5 0.090 10.92 19.26 0.978 2,274.9 21.30
The results of environmental indicators evaluation for total values per square meter are illustrated in Figure 2.
Environmental profiles of roof constructions show that variant3 achieved the lowest value of embodied energy
(620.279 MJ.m2) and variant 2 achieved highest value of embodied energy (1,589.89 MJ.m2). The best variant
from CO2 emissions is variant 1 with value of 76.97 kgCO2eq.m
2and the worst is variant 2 with value of 124.54
kgCO2eq.m
2. The best variant in term of SO2 emissions is variant 3 (0.3352 kgSO2eq.m
2) and the highest value of
SO2 emissions achieved variant 1 (0.5294 kgSO2eq.m
2).
Figure 2 illustrates EE and CO2 emissions and Figure 3 the SO2 emissions and ∆OI3STR. The ∆OI3STR indicator
describes the impact of building material in the given structure layer. The ∆OI3 indicator for one building material
layer indicates by how many OI3 points that layer of building materials raises the OI3CON of a construction. In other
words, if we eliminate one layer from a structure the OI3CON of the construction will sink by ∆OI3 points.
a) b)
Figure 2: (a) Embodied energy; (b) CO2 emissions of roof structures
a) b)
Figure 3: (a) SO2 emissions; (b) OI3CON of roof constructions
The percentage weights of environmental indicators are determined according to their impacts on the
environment, i.e. global impacts of EE and ECO2 and regional impact of ESO2. In Table 3 is shown significance
1024.27
1586.89
620.279
0
500
1000
1500
2000
Roof 1 Roof 2 Roof 3
76.97
124.54
95.53
0
20
40
60
80
100
120
140
Roof 1 Roof 2 Roof 3
0.3352
0.5294
0.4061
0
0,1
0,2
0,3
0,4
0,5
0,6
Roof 1 Roof 2 Roof 3
55.33
10.901
54.41
0
20
40
60
80
100
120
Roof 1 Roof 2 Roof 3
1258
weights of environmental indicators determined by Saaty method. Variant 3 (Table 4) is appeared to be the most
environmentally suitable. Determined values of environmental impacts for variant 3 are 620.279 MJ.m2, 95.53
kgCO2eq and 0.4061 kgSO2eq for embodied energy, CO2 emissions and SO2 emissions, respectively.
Table 3: Weights of relative significance for environmental indicators
Indicators EE ECO2 ESO2
Weights [%] 40 40 20
Table 4: Results of MCDA for environmental evaluation
Order Variant CDA Variant IPA Variant WSA VariantTOPSIS
1 Roof 1 0.8179 Roof 1 0.1672 Roof 1 0.8328 Roof 1 0.7489
2 Roof 3 0.9902 Roof 3 0.2291 Roof 3 0.7709 Roof 3 0.7399
3 Roof 2 4 Roof 2 1 Roof 2 0 Roof 2 0
In Table 5 is shown significance weights of overall indicators (environmental and thermo-physical indicators)
determined by Saaty method. Variant 3 (Table 6) is appeared to be the most suitable from environmental and
thermo-physical indicators.
Table 5: Weights of relative significance for determined indicators
Indicators EE ECO2 ESO2 d [mm] U [W/m
2.K] θsi [°C]
Weights [%] 20 20 10 10 20 20
Table 6: Results of MCDA for overall evaluation
Order Variant CDA Variant IPA Variant WSA Variant TOPSIS
1 Roof 3 2.0248 Roof 3 0.2647 Roof 3 0.7353 Roof 3 0.6368
2 Roof 1 2.8929 Roof 1 0.4318 Roof 1 0.5682 Roof 1 0,6203
3 Roof 2 3.3214 Roof 2 0.5524 Roof 2 0.4476 Roof 2 0.3708
4. Conclusions
The goal of this paper was to assess the alternative material solutions for roof assemblies to support decisions
made at the design phase of the project. Solutions were aimed at reducing the embodied environmental
impacts and improving energy performance. In this study cradle-to-gate life cycle analysis was used and
focused on environmental indicators such as embodied energy and emissions of CO2eq. and SO2eq. The
selection and combination of materials influences the amount of energy consumption and associated
production of emissions during the building operation phase. Methods of multi-criteria decision analysis (CDA,
IPA, WSA, TOPSIS) were used for the interpretation of results of assessments. Variant 3 of roof construction
designed from vegetation layer and thermal insulation of XPS with graphite is evaluated as the best solution.
Study (Vilcekova et al., 2015b) presents as the best solution also an extensive green roof, which is consisted
of clay plaster, a massive wood panel, straw bales between I-profiles, DHF boards, wooden formwork,
waterproofing, a drainage layer, and substrate. This variant was determined to be the best material
composition for both assessments (i.e., environmental evaluation and evaluation based on environmental and
thermal-physical parameters).
Acknowledgments
This study was financially supported by Grant Agency of Slovak Republic to support of projects No. 1/0307/16.
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