Sustainability index for roof covering materials

Charles C.V., Department of Building Economics, University of Moratuwa, Sri Lanka

(email: charles.vignes@gmail.com) Jeyamathan S.J.,

Department of Building Economics, University of Moratuwa, Sri Lanka (email:sjjeyamathan@yahoo.co.in)

Rameezdeen R. Department of Building Economics, University of Moratuwa, Sri Lanka

(email:rameez@becon.mrt.ac.lk)

Abstract

Construction is the largest user of materials of any industry. Hence selecting environmentally preferable building materials is one way to reduce the negative environmental impacts. The insufficiency of scientific data available in Sri Lanka for roof covering material selection is seen as a problem. The purpose of this study is to derive sustainability index for alternative roof covering materials which will assist the design team members to take informed decision. It was intended to take into consideration the environmental, economic and technical performance of the roof covering materials. Life Cycle Assessment (LCA) is adopted to assess the alternatives including the economic and technical performance. The attributes, Embodied energy, Reusability and Hazardous emissions to air measured in terms of Global warming potential (GWP), Acidification Potential (AP) and Criteria air pollutant (CP) are representing the Biophysical aspect of sustainability. The attribute, Life Cycle Cost represents the Economic aspect of sustainability and Functionality measured in terms of thermal performance represents the Technical aspect. According to the overall sustainability index derived, Asbestos takes the highest index while Zn/Al takes the second highest and Calicut tiles take the least index.

Keywords: Embodied energy, Roof covering materials, Life cycle assessment

1. Background

1.1 Sustainable construction

All economic sectors, including the construction industry, now face an inescapable challenge posed by the term “sustainability”. The construction industry is commonly considered as one of the largest industries in both developed and developing countries in terms f investment, employment and contribution to GDP. Consequently, the impact of the construction industry on the environment is also significant [7].

758

In 1987, the World Commission on Environment and Development (WCED) produced a publication entitled Our Common Future (WCED, 1987), which is referred to as the `Brundtland Report’. The publication described the concept of sustainable development as meeting the basic needs of all people and extending to all the opportunity to satisfy their aspirations for a better life without compromising the ability of future generations to meet their own needs [4].

The term `sustainable construction’, was originally proposed to describe the responsibility of the construction industry in attaining ‘sustainability’. First International Conference on Sustainable Construction was held in November 1994 in Tampa, Florida, United States of America. A major objective of the conference was `to assess progress in the new discipline that might be called “sustainable construction” or “green construction” [4].

Green design leads to sustainable development. Green design principles are adopted at design phases of construction. These principals are meant to affect the design so that the construction becomes sustainable.” Green design” is intended to develop more environmentally benign products and processes [3].

Hill and Bowen ended up in figuring out a framework for the attainment of sustainable construction. They outlined two multi-stage frameworks which would lead to sustainable construction. They are as follows,

• Application of Environmental Assessment (EA) • Implementation of Environmental Management system (EMS),

In the planning and design stages of projects, sustainable construction can be achieved by applying the principles, procedures and methods of Environmental Assessment (or Environmental Impact Assessment). A comprehensive traditional EA would evaluate alternatives for the sourcing of certain materials, such as the siting of quarries for stone aggregate, but would be unlikely to consider the life cycle environmental costs of most materials and products used in the construction process [4].

The traditional EA should be expanded to consider life cycle assessment of alternative materials and products which could be used in the construction process. In addition, the EA should ensure that efficiency is a key criterion in the use of water, energy and land. The results of such a life cycle assessment should influence the purchasing specifications for materials and products to be used. These examples illustrate how application of the principles of sustainable construction would expand the practice of EA towards the goal of attaining sustainability [4].

As Environmental assessment methods deal with assessing the whole building in terms of sustainability, they are inherent of the drawbacks that they do not consider the relative importance of criteria and they lack in considering whole life cycle of the product which is necessary as far as sustainable construction is concerned. Current methods for environmental assessment of buildings such as BREAM and BEPAC only focus directly two principles-

759

‘environment’ and ‘futurity’. They do not include criteria which explicitly assess buildings against either ‘equity’ or public participation [2].

1.2 Construction materials

‘If the construction industry is considered globally, it is by far the largest consumer of materials on planet Earth. The fact that construction materials are low-value should not surprise us; neither should it blind us to the importance of these materials. The sheer scale of consumption means that their use has a major impact on the environment, and economists, engineers and environmentalists have all devoted much thought to ways of measuring this impact. A number of criteria or indices of impact have been devised, with the objective of furnishing numerical data, which can help decision making. Qualitative assessments are useful up to a point, but if real progress is to be made it are necessary to quantify the impacts of materials consumption [6].

The concept of sustainable building incorporates and integrates a variety of strategies during the design, construction and operation of building projects. The use of green building materials and products represents one important strategy in the design of a building [5].

1.3 Building materials and sustainability

The overall performance of the building is the most important consideration in achieving more sustainable construction. Building materials play an essential role in increasing the energy efficiency of buildings and contributing to economic prosperity. Traditionally, materials selection for the design and construction of facilities has been based on economic and technological considerations, given the desired life span of a facility and the program of requirements and codes it must meet. In design environments where ecological, health, and ethical impacts are increasingly important, often the only way to choose from many different material alternatives is by relying upon on quantified professional judgment or past experience. The method should allow comparison of not only the technical performance and costs of materials, but also the immediate and long-term impacts their use has on the finite supply of natural resources and the ongoing needs for those resources by society. Together, these impacts comprise a measure of the sustainability of materials and should be given consideration during materials specification [1].

1.4 Aim of the study

Based on the background study, the necessity for scientific data which could assist the process of material selection was identified. And also it was found that such data do not exist in Sri Lanka for roof covering material which has a significant contribution to the sustainability of the whole building. Hence this study aims at developing a sustainability index for roof covering materials which could be used to assist selection.

The objectives for this study were as follows,

760

• To calculate the embodied energy of the roof covering material • To establish the level of reusability of the roof covering material • To calculate the emissions to air during the life of the roof covering material • To determine the life cycle cost of the roof covering material • To determine the functionality of the roof covering materials in terms of thermal

comfort

2. Research Methodology

Life Cycle Assessment was adopted as the methodology for this study. Life Cycle Assessment is a “cradle-to-grave,” systems approach for measuring environmental performance. The approach is based on the belief that all stages in the life of a product generate environmental impacts and must therefore be analyzed, including raw materials acquisition, product manufacture, transportation, installation, operation and maintenance, and ultimately recycling and waste management.

This study was limited to the following roof covering materials,

Asbestos corrugated sheets.

Zn/ Al sheets

Calicut tiles

According to the release ‘Census of Population and housing, 2001’by Census and Statistics department of SriLanka, the above mentioned roof covering materials has the highest usage in housing units in SriLanka. (Simple pitched roof with 30x100 ft plan area was considered for this study).

Selection of the manufacturing organizations

Manufacturing organizations were selected based on their level of maintenance of documentations. Organizations which had obtained SLS standards or the ones which were owned by government were assumed to have proper documentations maintained. Where the organization did not meet the above mentioned requirements, more than one organization was investigated to cross check the figures and the average figures are taken as final figures.

Data Collection Procedure

Semi structured interviews with the professionals or technicians who are familiar with the production processes were done and observations of the processes involved were also adopted as other means of data collection. In addition, documents were referred where ever necessary.

761

3. Methodology and limitation for each objectives

To calculate the embodied energy of the roof covering material

Process analysis has been adopted in calculating the embodied energy for this study because the simple reason that it produces accurate results. Process analysis was carried out only at the final factories at least one for each alternative. Embodied energy figures already available for intermediate products were directly used.

To establish the level of reusability of the roof covering material

Reusability was measured in terms of the importance to be reused. It was calculated by the fraction of prices of old roof covering material and the new roof covering material.

To calculate the emissions to air during the life of the roof covering material

Major portion of the emissions during the life time of the roof covering materials is by transportation and during manufacturing, since the roof covering materials alone do not emit any gasses through its life time. Transportation at the final manufacturing factory was the only transportation considered for this study. Transportations at intermediate productions are not considered due to time constraint. The emissions were related to environmental impacts which could be grouped under LOCAL EFFECTS and GLOBAL EFFECTS. For the transportation by sea, the same emission factors of vehicles were considered because of the non availability of emission factors and of the fact that the emissions by sea transportation are obviously more than that of the land transport.

LOCAL EFFECTS

Acidification Potential; Acidifying compounds may be in a gaseous state either dissolved in water or fix in solid particles.

Criteria air pollutants; are solid and liquid particles commonly found in the air.

GLOBAL EFFECTS

Global warming potential; was considered as Global effect. Global warming potential is represented in grams of CO2 emitted.

In order to express these three impacts in CO2 equivalent values, following normalisation values were used (Table 1). However each impact was given equal importance.

762

Table 1Normalization values for environmental impacts

Impact Normalization Values Global warming 25 582 640.09 CO2 equivalents/year/capita Acidification 7 800 200 000.00 millimoles H+ equivalents/ year/capita Criteria air pollutants 19 200.00 microDALYs / year/capita

To determine the life cycle cost of the roof covering material

Life cycle cost was considered. Initial cost involved the cost of roof covering materials with the costs of roof frame and roof plumbing. Discount rate is arrived at considering the commercial bank lending rates. The interest rate was taken to be 15 percent for this study which is the average of the period, 1977 – 2001.

To determine the functionality of the roof covering materials in terms of thermal comfort

Because a research had already been done comparing the values for thermal comfort of roof covering materials, it was decided to use those as secondary data for this study in order to meet this objective.

4. Data analysis

4.1 Embodied energy

Embodied energy of calicut tiles

Four cases were examined in order to determine the Embodied Energy (EE) of calicut tiles. Table 2 contains the energy consumption at different stages of life cycle based on the findings of case 1. This table displays the energy consumption for 11, 200 numbers of tiles considered. Findings on other three cases had slight differences because of the difference in technology and transportation distances. Average Embodied energy of the four cases investigated amounted to 26,170.29 MJ.

Table 2Energy at different stages of life cycle of calicut tiles

Stages of Life cycle Energy in (GJ) Extraction 0.396 Transportation 3.079 Drying 123.696 Firing 125.047 Pugging and extruding 6.104 Embodied energy 258.322

763

Embodied energy of asbestos sheets

Table 3 displays the energy consumption at different stages of life cycle and the total embodied energy of asbestos sheets based on the findings at the factory investigated for 800 Asbestos sheets of the size 10’x3’. Only one factory was investigated for asbestos sheets.

Table 3Energy at different stages of life cycle of Asbestos sheet

Stages of Life cycle Energy in GJ Production of asbestos ore 64.602Production of cement 129.616Transportation 7.279Manufacturing 3.330Embodied energy 204.827

Embodied energy of Zn/Al sheets

Table 4 contains the energy consumption at different stages of life cycle and the total embodied energy of Zn/Al sheets based on the findings at the factory investigated for 12 Tons of Zn/Al sheets of 0.35 mm thickness. Only one factory was investigated for Zn/Al sheets.

Table 4Energy at different stages of life cycle of Zn/Al

Stages of Life cycle Energy in GJ Production of high tensile steel 417.600 Transportation 7.256 Manufacturing 0.046 Embodied energy 424.902

4.2 Environmental impacts

Environmental impacts of calicut tiles

The following table displays the average impacts of the four cases investigated for calicut tiles.

Table 5Environmental impacts of calicut tiles

Effects g CO2 Equivalents Global warming 2,894,797.89 Acidification 17.28 Criteria air pollutants 1,176.89

764

Environmental impacts of asbestos sheets

Table 6 Environmental impacts of asbestos sheets

Effects g CO2 Equivalents Global warming 484,183.00 Acidification 6.51 Criteria air pollutants 443.47

Environmental impacts of zn/al sheets

Table 7 Magnitudes of the Environmental impacts of Zn/Al sheets

Effects g CO2 Equivalents Global warming 482,710.20 Acidification 7.79 Criteria air pollutants 529.73

4.3 Reusability

Table 8 Reusability of the alternatives

Roof Covering materials

Average market price of old material (Rs)

Market price of new material

Reusability

Asbestos sheets 56.25 110.00 0.51 Zinc alum sheets 398.50 907.00 0.44 Calicut Tiles 6.50 24.00 0.27

Value indexes for each variables considered

Table 9 Value index for Embodied energy

Roof covering material EE per 1 square meter of roof plan area

Value index

Asbestos sheets 134.90 100.00 Zinc alum sheets 1,448.43 9.31 Calicut Tiles 549.57 24.38

Value index = Minimum value of EE x 100

Embodied energy value

765

Table 10Value index for Global Environmental impacts

Roof covering material Global environmental impact in terms of CO2

Value index

Asbestos sheets 318.88 44.78Zinc alum sheets 142.81 100.00Calicut Tiles 49,211.56 0.29

Value index = Minimum value of Global impact x 100

Global impact

Table 11Value index for Local Environmental impacts

Roof covering material Local environmental impact Value index Asbestos sheets 0.30 50.00Zinc alum sheets 0.15 100.00Calicut Tiles 25.08 0.59

Value index = Minimum value of Local impact x 100

Local impact

Table 12Value index for Life cycle cost

Roof covering material Life cycle cost Value index Asbestos sheets 654,440.00 100.00Zinc alum sheets 2,803,186.00 23.34Calicut Tiles 1,040,520.00 62.89

Value index = Minimum value of Life Cycle Costing x 100

Life Cycle Cost

Table 13Value index for Reusability

Roof covering material Reusability Value index Asbestos sheets 0.51 100.00 Zinc alum sheets 0.44 86.27 Calicut Tiles 0.27 52.94

766

Value index = Reusability x 100

Amount of best case

Table 14Value index for Functionality

Roof covering material Functionality ranking Index Asbestos sheets 2 50.00 Zinc alum sheets 3 33.33 Calicut Tiles 1 100.00

Value index = Minimum rank value x 100

Functionality rank

The following table contains the sustainability indexes for each alternatives considered. This sustainability index was arrived at by summing the value indexes derived for each variable for each roof covering alternative considered.

Table 15 Sustainability index

Roof covering material Sustainability index Asbestos sheets 444.78 Zinc alum sheets 352.25 Calicut Tiles 241.09

The following radar chart, graphically illustrates the level of sustainability of the each roof covering material considered. More the area a material is dispersed from the centre of the graph, the more its sustainability.

767

0

10

20

30

40

50

60

70

80

90

100

EE

Global environmental

Reusability

Local environmental

Functionalty

Cost

Asbestos Zinc Calicut

Figure 1 Graphical representation of sustainability of roof covering materials

5. Conclusion

Based on the findings of this research, Asbestos sheets have the lowest embodied energy coefficient where as calicut tiles have the highest. It is because of the reason calicut tiles uses fire wood extensively for production. Asbestos sheets are less energy consuming. However this increased energy consumption could be off set against the calicut tiles’ longest life time.

As far as Global impacts are concerned, Zn/Al sheets have the lowest Global impact where as Asbestos and calicut tiles have higher Global impacts. The reason for the calicut tiles to have higher values for Global impacts (E.g. Global warming) is that it uses fire wood extensively which results in increased emission of CO2. Calicut tiles have the highest effect on the local environment too, due to its long transportation with large quantities and the immense use of fire wood. Asbestos sheets have high reusability index whereas the Zn/Al sheets have the second highest and calicut tiles takes the least. When comparing asbestos sheets and calicut tiles based on life cycle costing, asbestos sheets takes the lower NPV value, because of the reason that its frame cost is significantly less than that of calicut tiles’, even though it has one replacement during the life of the building. For Zn/Al sheets the cost of roof frame and roof plumbing are comparatively high and it has three replacements during the life time of the building. Hence Zn/Al takes the highest NPV among other two roof covering materials. calicut tiles have the

768

highest thermal performance reducing the cost of roof insulation and Asbestos and Zn/Al sheets have their thermal performance ranked second and third respectively.

The findings of this research are based on two limitations. Each attributes of sustainability was given equal importance; embodied energy and life cycle cost may not be of equal importance. No normalisation values were used in order to add the value indexes together to arrive at the sustainability index; reusability and environmental impacts are in two different units.

References

[1] Annie ,RP, Makarand ,H, Jorge ,A,V 2000, A Decision Support System for Construction Materials Selection using Sustainability as a Criterion,

[2] Cooper, I. 1997, Environmental assessment methods for use at the building and city scales: constructing bridges or identifying common ground, Evaluation of the built environment for sustainability, Chapman Hall,

[3] Hendrickson, C, Conway-Schempf, N, Lave, L, McMichael, F 1998, Introduction to Green Design, Green Initiated, Carnegie Mellon University, Pittsburgh PA

[4] Hill, RC, & Bowen, PA 1997, ‘Sustainable construction: Principles and framework to attainment’, Construction Management and Economics, vol.15, pp. 223-239.

[5] Integrated Waste Management Board, Green building materials. Retrieved July 06, 2007, from http://www.ciwmb.ca.gov/GreenBuilding/Materials/

[6] Sturges, JL 2000, ‘Construction Materials Selection and Sustainability, School of the Built Environment’, Leeds Metropolitan University, UK

[7] Zhang, ZH, Shen, LY, Peter, ED, Treloar, G, 2000, ‘A frame work for implementing ISO 14000 in construction’, Environmental management and health, vol. 11 (2), pp. 139-148.

769