Embodied energy and CO2 in UK dimension stone
N. Crishna*, P.F.G. Banfill** S. Goodsir*
*SISTech Ltd, Heriot-Watt University, Edinburgh, EH14 4AS
**School of the Built Environment, Heriot-Watt University, Edinburgh, EH14 4AS
Corresponding author: Professor PFG Banfill, School of the Built Environment, Heriot-Watt
University, Edinburgh, EH14 4AS, UK.
Phone +44 131 451 4648. Fax: +44 131 451 3161. Email p.f.g.banfill@hw.ac.uk
Abstract
A process based life cycle assessment of dimension stone production in the UK has been carried out
according to PAS 2050. From a survey of eight production operations, on a cradle-to-site basis for
UK destinations the carbon footprint of sandstone is 77 kgCO2e/tonne, that of granite is 107
kgCO2e/tonne and that of slate is 251 kgCO2e/tonne. These values are considerably higher for stone
imported from abroad due to the impact of transport. Reducing the reliance on imported stone will
contribute to emissions reduction targets as well as furthering the goals of sustainable development.
Keywords
Stone; Embodied CO2; Life cycle assessment; Carbon footprint
1
1. INTRODUCTION
Stone masonry is characteristic of the built environment in the north of the UK, and
especially Scotland. Indeed, for many centuries dimension stone1 has played a major
role in Scotland’s economic development and cultural heritage. In the 1850s there were
over 700 operational quarries but by 2000 this number had dropped to around 50
(Scottish Executive, 2006). This decline has been linked to a loss of craft skills, a
greater demand for industrially produced building materials such as brick and concrete,
and increasing imports of building stone. However these changes have had a cost in
terms of environmental impact and, in particular, carbon dioxide emissions. Despite this
decline, stone continues to be needed for new construction, where existing vernacular
styles are to be maintained, and for repair, maintenance and extension of historic
buildings and structures, in accordance with internationally recognised best
conservation practice.
The Climate Change (Scotland) Act 2009 lays out the Scottish Government’s
commitment to reduce greenhouse gas emissions in Scotland by 80% in 2050 (Scottish
Government, 2009). The relative roles of imported and indigenous stone in achieving
this target are unclear because, while there are clear guidelines and regulations for new
construction and there is established data about the environmental impacts of materials,
there is no similar data inventory for traditional structures. In particular, there is little
existing information on the impact of building stone (Hammond and Jones, 2008b).
1
Dimension stone is the result of quarrying a naturally occurring rock that can subsequently be fabricated
by hand or machine to a specific size or shape for use in construction. Building stone or freestone are
alternative terms.
2
This paper reports a study aiming to understand the impact, in terms of energy use and
greenhouse gases, of the quarrying and processing of natural stone used in the repair of
traditional buildings and construction of new buildings. It reports a process-based life
cycle assessment (LCA), carried out on data collected from quarries and stone yards, to
calculate the energy and carbon dioxide embodied in sandstone, slate and granite
dimension stone, and considers the role of imported stone. It presents, for the first time,
high quality data on Scottish and UK stone production, linked to a consideration of
transport and logistics.
2. LITERATURE REVIEW
2.1. Life cycle assessment and embodied carbon accounting
Accounting for the carbon footprint of products and buildings has become a well
developed approach to quantifying the success of climate change mitigation initiatives
(BSI, 2008a, 2008b). In the built environment, the focus is either on the emissions
during the operational life of the asset or on the embodied emissions defined as ‘the
total carbon dioxide equivalent that is emitted during the different stages of extraction,
processing, use and disposal of the material’ (UKWIR, 2008). Embodied energy
contributes 10-20% of the lifecycle energy consumption of conventional buildings but
the trend towards lower operational energy in highly efficient ‘green’ buildings is
increasing this proportion (Ramesh et al, 2010), with contributions reported up to 40%
(Chen et al, 2000) and 45% (Thormark, 2002) over a 50 year period. By definition an
embodied carbon analysis originates from a life cycle assessment (LCA). A recent
development in life cycle carbon accounting is the PAS 2050 standard (BSI, 2008a,
2008b).
3
2.2 Previous work on dimension stone
Much effort has been devoted recently to documenting the environmental impacts of the
different materials used in construction and most of the results are incorporated in
commercial software, handbooks (Anderson, 2002; Anderson et al, 2009), websites
(e.g. www.greenbooklive.com) and tools (e.g. BREEAM) which are widely used by
academia and industry. The ‘Environmental Profiles’ database for materials, produced
by BRE, is an attempt to produce standardised environmental data on construction
materials in the UK (Anderson et al, 2009). Embodied energy coefficients of materials
were initially produced for New Zealand (Alcorn, 1998, 2001, 2003). The Inventory of
Carbon and Energy (Hammond and Jones, 2008a, 2008b) summarises embodied energy
and CO2 coefficients for building materials, using data collected from primary and
secondary sources in the public domain, and employs a cradle-to-gate analysis for the
majority of the materials included. However, sandstone is not listed.
In contrast to these comprehensive listings for other building materials, there are fewer
studies of dimension stone in the public domain and those that exist differ in the use of
boundaries and resulting carbon and energy estimates. Alshboul and Alzoubi (2008)
and the University of Tennessee (2008a, 2008b, 2008c) have published some figures
from Jordan and USA respectively. The latter is an ongoing LCA study that has
collected industry data from 15 stone quarries and operations across the US and has
published results for granite, limestone and slate. In Scotland, a preliminary study of a
sandstone quarry by Venkitachalam (2008) found that transportation emissions were a
high proportion of the total carbon footprint.
4
Table 1 summarises published embodied energy and CO2 values and supports the view
of Hammond and Jones (2008b) who state that the data for stone LCA results are
‘generally poor’. Table 2 compares the activities and sources of CO2 included within the
system boundaries of these studies, and highlights the inconsistency across the different
work. It is worth noting that the ISO 14040 and PAS 2050 standards recommend the
use of wider boundaries, but in practice most studies have focused on first and second
order impacts (Alshboul and Alzoubi, 2008; Venkitachalam, 2008), and commonly
exclude the embodied CO2 associated with the manufacture and maintenance of capital
equipment and infrastructure.
Table 1. Reported embodied energy and CO2 values for stone
Source Study
Alcorn (2003)
Alshboul and Alzoubi (2008)
Venkitachalam (2008)
University of Tennessee
(2008a)
University of Tennessee
(2008b)
University of Tennessee
(2008c)
University of Bath ICE (2008b)
University of Bath ICE (2008b)
General
General
Sandstone
Embodied
Energy
(MJ/kg)
0.656
0.309
0.122
Embodied
CO2
(kgCO2/kg)
n/a
n/a
0.0095
Granite
5.908
0.62
Cradle-to-gate
Slate
0.208
0.028
Cradle-to-gate
Limestone
0.964
0.105
Cradle-to-gate
Granite
Limestone
0.1 to 13.9
0.3
0.006-0.78
0.017
Cradle-to-gate
Cradle-to-gate
Type of
stone
5
Boundaries
Cradle-to-grave
Cradle-to-site
Cradle-to-site
Table 2. LCA System Boundaries used by different standards and studies
PAS 2050
BRE
Material
Profiles1
University
of
Tennessee
studies2
Stone
Study:
Scotland3
Stone
Study:
Jordan4
Cradleto-grave
Cradle-tograve
Cradle-tosite
Cradle-tosite
Cradle-tosite
Cradleto-gate
Materials (used in the production
process)




Energy generated onsite




Use of electricity






Use of fuels on site






Use of fuels off site (transport)






Energy embodied in fuels


Energy use in offices and factories


Treatment and disposal of waste
products


Recovery of used products (including
reuse, recycling and energy recovery)


Manufacture of ancillary materials

Manufacture, maintenance and
decommissioning of capital
equipment

Manufacture, maintenance and
decommissioning of capital
infrastructure

Boundaries include
Any other processes within the life
cycle which are associated with GHG
emissions
ISO
14040




1
Anderson et al, 2009; 2 University of Tennessee 2008a; 2008b; 2008c; 3 Venkitachalam, 2008; 4 Alshboul
and Alzoubi, 2008
3. METHODOLOGY
3.1. System boundaries
A process-based LCA approach to extraction and processing has been used to quantify
the carbon footprint of dimension stone. In order to produce consistent, comparable
results, the boundaries and guidelines specified in PAS 2050 have been followed as far
as practicably possible with any deviations from the PAS 2050 methodology identified
below.
6
As a first step all the materials, activities and processes that contribute to the production
of dimension stone were identified and a process map developed and verified in
discussion with quarry and stone yard owners. This defines the flows of energy through
the life cycle (Figure 1).
Figure 1. Process map of the life cycle of dimension stone
Quarrying
Overburden
removal
Quarry
backfilling
Scrap stone
Crushing at
crushing facility
Extraction
Transport
Processing
Primary
processing
Quarry
backfilling
Scrap
stone
Transport
& storage
Secondary
processing
Crushing at
facility
Other
disposal
Distribution
Finishing and
packaging
Transport
to site
The second step was to define the system boundaries for the cradle-to-gate and cradleto-site LCA. The boundaries of the cradle-to-gate analysis conducted in this research
are consistent with the Business-to-Business (B2B) approach outlined in PAS 2050 and
7
the main inputs are shown in Figure 2. Four sources of energy use were excluded from
this study: (i) the manufacture and maintenance of machinery and vehicles, (ii) water
Figure 2: System boundaries - Inclusions and exclusions in each stage of the life cycle
Cradle-to-Site
Cradle-to-Gate
QUARRYING
PROCESSING
DISTRIBUTION
Included
Included
Included
 Energy use by heavy
machinery
 Energy use by on-site
transport: lorries and
loaders
 Energy use for backfilling
 Energy used to dispose of
waste/scrap
 Use of black powder
 Energy use by on-site
machinery e.g. primary
and secondary saws etc.
 Energy use by on-site
facilities e.g. heaters, dust
extractors
 Energy use by on-site
offices
 Energy used to dispose of
waste/scrap
 Energy use by on-site
transport: forklifts
 Energy used to transport
material to site/storage
Excluded
 Energy
embodied
in
machinery used on site
 Energy embodied in onsite transport: lorries and
loaders
 Energy embodied in black
powder production
Excluded
 Energy embodied in
vehicles
used to
transport stone to yard
Excluded
 Energy embodied in
machinery used on site
 Energy embodied in water
used on site
use on site, (iii) construction and maintenance of buildings and (iv) the production of
black powder / explosives. Excluding energy embodied in the production of black
powder was due to lack of existing information on explosives. As the amount of
8
explosive used at the quarry (compared to the energy use) is minimal this exclusion has
not made a material difference to the results of this work and is considered to be in
accordance with PAS 20502. For the cradle-to-site analysis, the cradle-to-gate figures
have been supplemented with additional data associated with the transport of stone to a
number of example destinations in Scotland, considering only direct fuel use, excluding
manufacture and maintenance of vehicles.
The functional unit adopted for this work is kilograms of carbon dioxide equivalent per
tonne of finished dimension stone (kgCO2e/tonne) and it is assumed that the output
product consists of regular blocks finished flat on all six faces, but without significant
decorative treatment. The only process emissions associated with the production of
stone are from the combustion of black powder at the quarry. The emission factors for
fuels and electricity used include associated NO2 and CH4 emissions.
3.2. Data collection and quality
Based on the process map (Figure 1) survey questionnaires were developed for owners
of quarries and stone processing facilities to report fuel use and production for calendar
year 2008 and to state the main destinations of their stone products. Sandstone, granite
and slate operations across Scotland, the UK and in the Republic of Ireland were
contacted, with an emphasis on sandstone quarries, and the response rate is shown in
Table 3. Eight operations, covering all three stone types and a range of scale of
operation, were visited to contextualise the data. The relatively low response rate (38%)
is probably due to the small scale and seasonal nature of some operations, and a
2
Sandstone and granite quarries were seen to use between 50 and 125 g of black powder per tonne of
stone quarried as compared to diesel usage of between 2 kg and 7 kg per tonne. Even if the embodied
energy in black powder was equal that of diesel, the increase in the overall results for sandstone and
granite would be 0.01% and 0.04% respectively.
9
perception by operators that finding data would take significant time out of their
business. The majority of the activity data from the 12 returns received was based on
actual records kept by the organisation, rather than estimates. However, the data on
main destinations for stone products was based largely on estimates.
Table 3. Number of UK stone operations contacted and responses received
Type of
stone
Sandstone
Slate
Granite
No. of operations
contacted
Quarry
Stone
and yard
yard
13
6
6
n/a
6
n/a
Responses received
Quarry
and yard
4
2
3
Stone
yard
3
n/a
n/a
Location
Scotland and Derbyshire
Cumbria and Wales
Cornwall and Ireland
The primary data was supplemented by secondary data on emission factors drawn from
standard sources, including Defra, European Commission and industry-specific sources
(see Table 4). The only exception to this was the emission factor for black powder
which was developed stoichiometrically.
3.3. Calculation of embodied CO2
For each stage in the life cycle, the energy used for each activity was multiplied by the
appropriate emission factor (Table 4) and summed. The overall figure was then
allocated among products and by-products using the system expansion method (BSI
2008b) and the total tonnage of quarried stone or stone product. Overall Scottish and
UK embodied carbon for each stone type is an output-weighted average of all the
quarries and stone yards who provided data.
10
Table 4. Sources of secondary data used in this study
Emission Factors
Type of
factor
Applied to
Source
Fuels: diesel, gas
oil, fuel oil, LPG
Combustion
factor
Cradle-toGate analysis
Defra / DECC (2009)
Fuels: diesel, gas
oil, fuel oil
Life-cycle
factor
Cradle-toGate analysis
European Commission (2008)
Fuels: LPG
Life-cycle
factor
Cradle-toGate analysis
World LP Gas Association (2008)
Freight Transport:
road (UK)
Tonne.km
factor
Gate-to-site
analysis
Defra / DECC (2009)
Freight Transport:
road (worldwide)
Tonne.km
factor
Gate-to-site
analysis
IFEU (2008). (This work was
commissioned by various EU freight and
rail organisations.)
Freight Transport:
sea
Tonne.km
factor
Gate-to-site
analysis
Defra / DECC (2009)
‘Black Powder’
explosive
Combustion
factor
Cradle-toGate analysis
Developed stoichiometrically from
process chemistry.
3.4. Modelling transport impact of imported stone
It was particularly important to understand the carbon impact of transport because of
the volume of stone now being imported from abroad. Although HM Revenue and
Customs maintains detailed data on imports and exports, there is very little collated,
published information on the volume of stone imports into the UK. Industry reports
(Natural Stone Specialist, 2006) and interviews with project stakeholders identified
Portugal, Spain, Italy, and Poland in the EU and Brazil, India and China as principal
sources, so four representative countries were chosen – Spain, Poland, India and China.
Inconsistent disaggregated data and the variable data quality made it unfeasible to
calculate top-down CO2 figures for these countries so their dimension stone industries
were investigated. A desk-based review, followed up with phone interviews with
industry professionals in the UK and in each country established the structure and scale
of the stone industry, the types of stone produced and exported, the location of the main
11
stone producing areas in each country, the modes of transport and the routes followed
within the country and to the UK. The average road and shipping distances were used to
model the CO2 associated with the transport of stone to two hypothetical destinations in
Scotland: Edinburgh, for all three stone types, and Aberdeen, for granite only. (Granite
is the predominant stone in Aberdeen’s built environment.) It is assumed that stone is
quarried and processed within the country of origin before export to UK and that the
shortest practicable transport routes are followed.
4. RESULTS AND COMMENTARY
4.1. Carbon footprint of natural stone from the UK
Table 5 presents the embodied CO2 associated with sandstone, granite and slate
produced by quarries and stone processing facilities in the UK. The figures are outputweighted and based on data collected for the calendar year 2008. The cradle-to-gate
values in Table 5 reflect the energy used in quarrying and processing of the stone, while
the cradle-to-site figures reflect the transport of stone within the UK.
Table 5. Cradle-to-gate and cradle-to-site embodied carbon
Stone type
Embodied carbon (kgCO2e/tonne)
Cradle-to-gate
Cradle-to-site
Sandstone
64.0
77.4
Granite
92.9
107.5
Slate
232.0
251.8
Slate has the largest footprints of the three stones and its cradle-to-gate footprint is
inflated by the amount of waste that is associated with quarrying and processing.
Quarry operators’ estimates for slate waste are 85% compared to 29% for sandstone and
47% for granite. Taking these proportions into account to calculate the footprint on a
total production basis (i.e. including waste) reverses the order with slate having the
12
lowest footprint. The scale of wastage can be attributed to the thinly bedded and easily
breakable nature of slate, requiring much more bed rock to be quarried and processed in
order to produce slate product, as compared to sandstone and granite. We return to the
issue of waste later.
The cradle-to-site figures are based on data collected from each stone yard on the mode
of transport and destinations for stone processed in the yard in 2008, and therefore
reflect the average impact of transport to construction sites (mostly within the UK). For
slate this is slightly higher than granite and sandstone comparators due to the clustering
of slate quarries in the study (Cornwall and Cumbria) and the UK wide distribution
(and associated carbon cost of transport) of the slate product from these operations. For
most of the Scottish sandstone operators, distribution is largely regional or local.
Figure 3 shows the disaggregated impacts for each stone type and the allocation of CO2
to the main stages in the life cycle of the stone. The largest component is attributable to
processing, mostly due to the number of stages and the variety of machinery associated
with each stage in processing. The largest source of processing emissions is the
electricity to run stone preparation machinery, dust extraction devices and water pumps.
13
Figure 3: Disaggregated embodied CO2 in UK stone
4.2. CO2 associated with the import of natural stone
Table 6 presents the results of the transport modelling from various countries of origin
on the cradle-to-site CO2 emissions. The impact of transport increases with distance
from the country of origin, with transport from China resulting in an over 550%
increase while transport from Spain increases the embodied CO2 by 7% for slate and
2% for granite which is equivalent to transporting stone end to end in the UK. For stone
sourced from Spain and Poland, most of the transport impact is attributable to road
journeys within each country, and although the journey by sea to the UK is
considerably longer the CO2 impact is lower, due to the lower CO2 impact (per tonnekilometre) of shipping. For stone sourced from India and China, the largest contribution
is attributable to shipping over the long distances involved.
14
Table 6. Effect of transport from different countries of origin on embodied CO 2 in
dimension stone delivered to Edinburgh and Aberdeen
Stone type
UK Cradle-to-Site*
(kgCO2e/tonne)
Cradle-to-Site from countries indicated
(kgCO2e/tonne)
Spain
Sandstone
77.3
133.7
Granite
158.0
161.2
Slate
297.4
318.2
Poland
188.0
India
China
312.3
504.0
336.5
415.5
568.1
* These figures are based on UK cradle-to-gate (Table 5) plus transport to development sites in
Edinburgh and Aberdeen.
Although the results presented here are estimates, they highlight the very large CO2
impact of transport of imported stone. In Table 6 the shortest route and simplest
logistical scenario has been assumed, whereas in reality the transport impacts associated
with the global stone trade may be even higher due to the reported practice of shipping
rough stone from Europe to India or China for processing (taking advantage of lower
labour costs) before exporting it back to the EU.
4.3. Uncertainty of results and sensitivity analysis
The quality of any LCA is directly related to the quality of the inventory data. Weidema
and Wesnaes (1997) describe data quality indicators based on reliability, completeness,
and temporal, geographical and technological correlation. They give definitions for five
levels of data quality from ‘excellent’ to ‘unreliable’. A high proportion of the input
data for the UK study was based on bills and records kept by the actual quarry operators
for 2008 for the area of study, and these data are based on a small but representative
sample of quarries. Therefore the confidence that can be attached to this part of the
work is high and under this classification the data quality is excellent.
15
The results for production and processing in other countries are necessarily less reliable
because of differences in methods between countries. Nevertheless, as shown in Table
6, even if the cradle-to-gate component in India and China could be reduced to zero, the
transport to site would still exceed the total for UK production.
The results of the analysis were found to vary with the method used to allocate between
stone products and by-products. When allocating by weight or volume of stone, the
carbon footprints of all three stone types were seen to be significantly less than the
results presented here, whereas when allocating by financial value, the reverse was
seen, especially in the case of slate where slate by-product i.e. inert fill material is sold
at a much lower price than slate product (which is the most expensive of all three stone
types). The system expansion method, used in this study, is based on the assumption
that by-products of a process are displacing other materials in the global market and
therefore a carbon credit is assigned to the main product in question. This method was
selected for this work as the data on embodied carbon values for fill materials and
aggregates are of better quality and are consistent across different databases, whereas
there is a lack of recorded information on standardised prices across the stone industry
and the price of the same product varies from yard to yard.
5. DISCUSSION
5.1. Comparison with other UK construction materials and possible improvements
It is clear that dimension stone is a low carbon construction material when compared to
other UK materials (Table 7). The main impacts are related to processing, transport to
site and the volume of waste stone produced, and, clearly, quarrying and processing of
the sandstone and granite are not very energy intensive compared to the production
16
processes of other materials like brick or concrete. Provided the stone is locally or
domestically sourced the carbon emissions associated with it are less than other
building materials.
Table 7. Embodied carbon associated with common construction materials (adapted
from Hammond and Jones, 2008b)
Material
Embodied Carbon
(kgCO2/tonne)
64
Sandstone
Granite
93
Marble
112
General Concrete
130
Cement Mortar - (1:2:9 Cement:Lime:Sand mix) (1)
143
General Clay Bricks
220
Slate
232
Timber: Sawn Softwood
450
Timber: Sawn Hardwood
470
Facing Bricks
520
General Building Cement
830
Steel: Bar and Rod (2)
1710
Steel: Galvanised sheet (3)
2820
Source
This work
Hammond,
Jones
This work
Hammond,
Jones
All figures are for Cradle-to-gate, (1) This is the closest mortar to those used for traditional stone listed
in the Inventory, (2) Typical values, (3) Primary steel
Slate, on the other hand, has an impact comparable to materials like brick and concrete,
because of the amount of waste stone produced by slate quarries and yards. While slate
waste can be used in lower-grade by-products, its tonnage outweighs by many times the
desirable architectural slate and this increases the overall energy consumption.
While most of the quarries and yards investigated produced virtually no waste material,
operators having found ways of using all waste stone produced during the processing
stage so that almost nothing goes to landfill, there is clearly room for improvement in
the slate sector. Slate scrap is used as landscaping material and slate dust has been used
17
as filler in plastic products (Gutt et al, 1975) but further efforts to exploit the waste will
reduce the impact of slate. Sandstone and granite operators use larger pieces of waste
to produce rough walling stone for local farms, while the finer scrap is used to produce
aggregate.
The main uses of energy at a dimension stone quarry are diesel and petrol for drills,
excavators, front end loaders and dump trucks, and a limited amount of explosives. The
main uses of energy in the stone yard are electricity for the stone-processing machinery,
pumping of water and extraction of dust; diesel and gas oil / fuel oil for finishing and
shrink wrapping of products; LPG or diesel for heating the yards; and diesel or petrol
for transporting the finished stone. Electricity is also used in any office or retail
buildings attached to the yard. Clearly there is potential for further reducing the
emissions from stone production by using electricity generated from renewable sources,
some of which could be used to charge hybrid electric vehicles for transport.
For example, the cradle-to-gate embodied CO2 of sandstone (64 kgCO2e/tonne) includes
116 kWh/tonne of electricity, which accounts for 60 kgCO2e/tonne, taking the current
UK emissions factor for network electricity as 0.52 kgCO2e/kWh. If this were replaced
by renewably generated electricity at a very low emission factor, it would be possible to
further reduce the impact of sandstone. Even without much progress towards a zero
carbon UK electricity supply network this could be achieved by local installations at
quarries and stone yards. This has been achieved at a sandstone quarry and stone yard in
Spain, claimed to have zero impact, by using photovoltaically generated electricity
(Areniscas, 2008). Some quarries may be able to exploit local watercourses to generate
18
small scale hydro-electricity. These measures offer the possibility of reducing the
impact of stone production to low levels.
5.2. Impact of importing stone to Scotland
The transport of imported stone has a very big effect on the overall footprint of stone,
with by transport from India or China to Scotland increasing it several-fold. Even if the
cradle-to-gate emissions embodied in stone were to be reduced to a minimum or zero,
the transport to Scotland would still have a significant CO2 impact.
The transport estimates are also conservative in that they assume the shortest transport
route between the country of origin and Scotland, and the simplest scenario, whereby
stone that is quarried in one region is processed in the same region before being
transported to the UK. In reality rough blocks are transported long distances before
being processed, and then transported again before being used at a construction site. For
example, in 2008 raw granite and marble block was exported to China from Italy,
Egypt, Iran, Brazil and India, processed in China, and then re-exported to countries in
the EU and to the USA (IMM 2009). This trend of exporting rough block to the Far
East and Brazil for processing before importing the processed stone to the EU and the
US is well established in the global stone trade (AIDICO, 2008; IMM, 2009; Natural
Stone Specialist, 2009).
It is logical to assume that the cradle-to-gate carbon footprints of stone from countries
like India, China and Brazil would be lower than the UK footprints presented in this
paper due to economies of scale and an expected greater dependence on manual labour.
However, the investigation of the main stone producing and processing areas in China
19
and India during this research showed considerable transport by road of rough block
from one area to be processed in another. In China, granite is extracted from 27
different areas in eastern, central and northern regions, whereas processing hubs are
restricted to two or three areas in southern China (Natural Stone Specialist, 2009). The
distances covered (and the associated impacts of transport) are therefore large and this
would increase the carbon footprint of the stone significantly.
5.3. Limitations of this study
One potential limitation of this work is that there is no differentiation between stone
products. The functional unit was chosen as a tonne of stone production, and the results
given are for the weighted average of all dimension stone products produced at the
stone yards which took part. Alternative functional units could be envisaged, such as for
example a square metre (m2) of façade replacement in repairs, where the weight of the
stone used will depend upon the thickness required. It seems reasonable to expect that
more processing per tonne will be needed for thinner stonework, and that the carbon
footprint would be higher for a thinner product. This of course is unlikely to affect the
transport element of any stone product.
Slate is predominantly used in roofing and here an appropriate functional unit would be
a square metre of roof covering. At every point on a slate roof there is a double layer of
slates each 5 – 10 mm thick, so 50 kg is used per m2 of roof. In contrast, interlocking
concrete tiles are 30 mm thick and, if overlapped by 25% of their area, 85 kg is used per
m2. Finally, galvanised steel sheet is 1 mm thick and, if overlapped by 10%, 8.5 kg is
used per m2. Using the data in Table 7 for these quantities of material suggests that the
embodied carbon of a slate roof is the same as that of a concrete tile roof at about 11
20
kgCO2/m2, half that of a galvanised steel roof (24 kgCO2/m2). Therefore, despite the
amount of waste produced, slate compares favourably with the alternatives.
The study explicitly excluded any consideration of the technical suitability of the stone
concerned. For repair, maintenance and extension of historic buildings and structures
material must be sourced from the original quarries or from compatible sources to
accord with internationally recognised best conservation practice. Where the original
stone is no longer available this may be difficult because compatibility is not just a
matter of appearance or texture but has a technical dimension: introduction of stone
with markedly different porosity and sorptivity can hasten the decay of adjacent
material, leading to further problems (Hyslop, 2004). This has the potential to hinder
the conservation of the very buildings that contribute to quality of life and attract the
tourists that benefit Scotland’s economy (Scottish Executive, 2006).
Finally, this paper does not consider the economic issues surrounding stone production
and use, and it would be worthwhile to undertake a life cycle cost analysis to
understand the economic drivers that contribute to the overall emissions associated with
both new construction in stone and the repair, maintenance and conservation of existing
stone masonry.
5.4. Implications for policy
In global terms, the implications of these results are clear cut: increasing production and
use of indigenous stone at the expense of imports will reduce the overall carbon
footprint of the dimension stone used in the Scottish and northern UK built
environment. In terms of the domestic Scottish target of reducing CO2 emissions, the
21
overall footprint of stone construction depends on whether the emissions from
international shipping are included, as required by the EU Emissions Trading Scheme.
While the issues of international trade are complex and beyond the scope of this paper
(see for example Sanchez-Choliz and Duarte, 2004, Weber et al, 2008, Andersen at al
2010), it may be noted that Li and Hewitt (2008) compared imports from China against
domestic production and concluded that the UK effectively reduced its emissions by
about 11% in 2004 by sourcing goods from China. Depending on the accounting
approach adopted, it is possible that, in the immediate vicinity of the port of arrival,
imported stone will have a lower allocated footprint than indigenous stone, but the
contribution of transport within Scotland is such that imported stone’s footprint will
mostly exceed that of locally produced stone.
As a low energy material, dimension stone has a considerably lower carbon footprint
than alternative construction materials available within the UK, a comparison that is not
obscured by the international issues. For sustainable construction, it will be preferred to
brick and concrete, its principal competitors. Switching from these materials to
dimension stone and roofing, wherever it is technically feasible, will directly contribute
to the emissions reduction target. There is also an opportunity to further reduce the
carbon impact of the Scottish stone industry by supporting the widespread deployment
of micro-renewable technologies among stone quarry and stone yard operators, most of
which are located in rural areas and can be classed as small businesses. Some support is
available already under the Scottish Government’s Rural Priorities scheme (Scottish
Government, 2010a) but a more targeted approach such as exists for the agricultural
sector may be more effective in reducing the carbon emissions from the Scottish stone
industry. This would not only aid Scotland’s carbon reduction targets, but would also
22
support the government’s latest commitment to producing 80% of electricity from
renewable sources by 2020.
The wider case for promoting the use of indigenous Scottish stone over imported stone
is more closely related to the issue of sustainable development, which may be viewed
against three criteria – economic growth, environmental protection and social progress.
Stone quarries are typically rural operations and with the stone being used locally the
income stays within the local community, which benefits economically. The use of
local stone contributes to the quality and distinctiveness of the built environment, which
results in economic growth through tourism and leisure visitors. The environment is
protected because not only is stone a low impact, low carbon material but use of
resources is maximised, with waste reduced, and shorter travel distances for materials.
Use of compatible stone prolongs the lifetime of existing buildings, maintains the built
heritage and fosters the inhabitants’ sense of place. Social progress is facilitated
because quarries can offer skilled employment in typically rural areas, preventing
outward migration. Scottish dimension stone quarries are good neighbours with
minimal adverse impact on communities. The health and safety of the workforce is
high, without exploitation, nor the need to subscribe to ethical trading initiatives in
originating countries as described in eg Marshalls (2008).
Scottish planning guidance (Scottish Executive, 2010b) states that new housing should
take account of the scope for using local materials and that dimension stone and slate
are particularly important because they contribute to the Executive’s policies on the
historic environment, on improving housing conditions, on sustainable development
and on the design of settlements. Therefore reserves should be safeguarded in
23
development plans because reopening dormant sites and securing active sites is
important in providing for future supply. It notes that reserves are often worked on
small sites, in limited quantities and intermittently over long periods and therefore
planning authorities should ensure that conditions do not impose undue restrictions on
such operations. Scottish dimension stone tends to meet these objectives better than
imported material and the technical need for compatibility adds a further stimulus to
policies fostering the use of indigenous stone in Scotland.
6. CONCLUSIONS
A process-based life cycle assessment of dimension stone production in the UK has
produced high quality data for the carbon footprint of sandstone, granite and slate for
use in Scotland. On a cradle-to-site basis for UK stone delivered to UK destinations the
carbon footprints of sandstone, granite and slate are 77, 107 and 251 kgCO2e/tonne
respectively. Importation of stone from abroad considerably increases these values and
with conservative assumptions about the embodied CO2 in shipping, road transport and
logistics the cradle-to-site footprint rises from 134-318 kgCO2e/tonne for Spain up to
415-568 kgCO2e/tonne for China. Increasing the use of indigenous stone in Scotland
will help reduce Scotland’s carbon footprint and contribute to the Scottish
Government’s emissions reduction targets. More widespread use of local stone will also
help further the goals of sustainable development in the country and support the
planning system.
7. ACKNOWLEDGEMENTS
We thank the quarry and processing facility owners and managers in Scotland, England,
Northern Ireland and the Republic of Ireland who gave their time and participated in
24
this project. We do not name them but appreciate their contribution. We thank Craig
Kennedy, Historic Scotland, Colin Tennant, formerly Scottish Stone Liaison Group,
and Peter Harrison, Harrison Stone Consultants for their support and interest, without
which the project would not have been possible. We thank Katarzyna Przybycien and
Sean Zhang for information on the stone industry in other countries. The project was
supported financially by Historic Scotland.
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