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GREEN MAINTENANCE FOR HISTORIC MASONRY

BUILDINGS: AN EMERGING CONCEPT

Alan M Forster - a.m.forster@hw.ac.uk (Corresponding Author)

Kate Carterβ - k.carter@ed.ac.uk

Phillip F G Banfill

- p.f.g.banfill@hw.ac.uk

Brit Kayan γ - bk41@hw.ac.uk

School of the Built Environment, Heriot-Watt University, Edinburgh, United Kingdom

βEdinburgh School of Architecture and Landscape Architecture, University of Edinburgh, United

Kingdom

γ Faculty of the Built Environment, University of Malaya, Kuala Lumpur Malaysia

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GREEN MAINTENANCE FOR HISTORIC MASONRY

BUILDINGS: AN EMERGING CONCEPT

Abstract

Maintenance is essential for long term performance of any building. It enables the simultaneous

retention of value in a structure and contributes to a countries’ Gross Domestic Product. The

efficacy of maintenance interventions for historic buildings can be assessed based on cost,

conformity to building conservation philosophy and increasingly, environmental sustainability.

Carbon and energy savings in historic buildings are considered as difficult to achieve due to

limited retrofitting capability. Maintenance is one mechanism by which it may be possible to

achieve carbon savings, initiated through necessary proactive and reactive regimes.

A model for evaluating the efficacy of maintenance interventions is proposed, utilising material

life cycle data and cradle to site techniques for embodied CO2 determination. Additionally,

formulaic expressions can be used to calculate the relative merits of any selected maintenance

intervention over a given timeframe. Internationally, the model represents a framework for

selection of maintenance interventions in relation to cost, philosophy and carbon emissions. The

strength of this integrated multi-criteria approach to decision making is that it enables carbon

emissions to be accounted for in the determination of efficacy of masonry repair types.

Key words

Green Maintenance, Carbon reduction, longevity, life cycle assessment, philosophy

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1. Introduction

Maintenance of stonework is crucial in ensuring that the financial, environmental and social

capital invested in masonry buildings worldwide is not wasted. Traditionally, maintenance has

been recognised as a cost commitment associated with a building (Wise, 1984), but any

maintenance intervention also has a carbon commitment and there is an increasing international

focus on reducing carbon in the built environment (Stern, 2006). This largely centres on new

build, and the upgrading and maintenance of existing buildings receives little attention in the

context of carbon reduction although it contributes to the lifetime carbon emissions in a way that

cumulatively may be significant. Maintenance is essentially a way of prolonging the life span of a

building. Associating maintenance with a life cycle carbon approach leads to the concept of

‘green maintenance’, which can be seen as maintenance with minimal environmental impact.

The objective of this paper is to study different maintenance regimes over a 100 year period to

demonstrate how this concept can model the associated carbon commitment and facilitate options

appraisal for historic buildings.

2. Maintenance of Historic Buildings: Cost, Philosophy, Environment

Ageing of buildings results in decay and deterioration. William Morris, founder of the Society for

the Protection of Ancient Buildings (SPAB) in 1877, endowed the organisation with the aphorism

‘to stave off decay with daily care’, reflecting the important role maintenance plays in retaining

the value embodied in the historic fabric (SPAB, 2008:1).

Internationally the importance of building maintenance is well recognised as an essential

mechanism for retaining cultural heritage and preserving the capital (financial, social and

environmental) associated with the building fabric. This has been embedded in the principal

building conservation legislative frameworks and charters (Bell, 1997; BS7913, 1998). A main

tenet of these frameworks is sustainability, but this tends to be seen in terms of retention of the

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building, i.e. prolonging the life of cultural assets (ICOMOS, 1993), rather than the processes in

maintaining the structure. The adoption of the ‘World Heritage Convention’ by UN member

states is aimed at promoting conservation of historic buildings and sites (UNESCO 1972), and

this has resulted in four decades of work to preserve buildings of international importance.

Various proactive schemes [Monumentenwacht (2000); Raadvad Bygningssyn] have been

successfully implemented to achieve conservation maintenance objectives. In Italy the Merlioni

Laws have been enforced since 1990 to implement maintenance activity (Maintain Our Heritage,

2004). Australia has implemented the ‘Heritage incentives programme’ acting as a stimulus for

maintenance activity (Office of Environment & Heritage). Malaysia has implemented a

governmental ‘funding allocation programme’ that targets funding towards early maintenance

interventions (Kayan, 2006). Historic Scotland (2005; 2007) targets advice to encourage

maintenance of historic masonry. Underlying this worldwide interest, is an increasing focus on

existing buildings and their relative historic importance. Innumerable unlisted, masonry structures

form a large part of our built environment, creating a sense of place and continuity of

architectural form (BS7913: 1998). Whilst these buildings do not all have legislative protection,

they do need appropriate high quality maintenance to ensure satisfactory long term performance

and aesthetic continuity.

While maintenance is recognised as beneficial, it can be difficult to implement for many reasons

(Forster and Kayan, 2009). Historic Scotland (2008:28) indicates that “there can be difficulties in

identifying a generic hierarchy of maintenance interventions within historic buildings”. The

approach taken to evaluate masonry repairs is almost always set within the parameters of

budgetary constraints, but maintenance of historic masonry buildings must also be implemented

within a framework that is soundly based on ethics and principles. Forster (2010a:92) states that

‘repairs selected, based upon the ethical concepts and a combination of the principles, should be

defensible and should in theory lead to naturally ‘good’, well founded conservation

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interventions’. The essential principles of building conservation philosophy are: least

intervention; like-for-like material replacement; honesty and distinguishability; integrity;

reversibility; respect for historic patina; and respect for traditional craft skills (Bell, 1997). The

success of a maintenance intervention is therefore evaluated not only on the quality of the repair,

but also on its conformity to these principles.

Retention of traditional masonry buildings is important not only from a cultural perspective but

also from an economic standpoint. The scale of this issue is reflected in the fact that 50% of

national wealth across Europe is contained within the existing built environment. Maintenance of

these buildings contributes significantly to Gross Domestic Product (Balaras et al., 2005). A lack

of regular maintenance significantly devalues these assets due to associated premature

deterioration. Within the United Kingdom, maintenance accounts for half of the total expenditure

on construction. There are nearly 450,000 listed buildings and 10.6 million pre-1944 buildings

within the UK, making up the largest part of the built environment (Maintain Our Heritage,

2004). The financial value of repair works was estimated at £36 billion in 2002 (at 2002 prices)

(DTI, 2002; Arup, 2003). Of this value masonry is not an insignificant sum, and it has been

estimated that in Glasgow alone, the cost of masonry repairs required over a 20 year period is

approximately £600 million (at 2010 prices) (SSLG, 2006). Other major cities with a tradition of

masonry construction may require similar investment, contributing significantly to many

international economies. Nevertheless, despite its importance, and the size of the sector,

maintenance appears to be poorly regarded by the public and construction industry alike. The

financial cost of masonry repair using traditional materials and techniques is often greater than

with modern materials, due to the higher cost of materials and the need to use specialist

subcontractors operating within a perceived niche market (Forster and Kayan, 2009). However,

Cassar (1994:42) emphasises that ‘with dwindling resources and escalating cost, pragmatic

choices are often necessary and inevitable’. Even so, interventions that fit within the

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philosophical framework are generally of high quality, are more compatible with the existing

fabric, and endure longer than insensitive, often inappropriate repairs.

Adding to the complexity of prioritisation within the philosophical and economic context, a third

and emerging factor in the evaluation of maintenance is environmental sustainability. This paper

seeks to overlay environmental impact on to this framework and attempts to evaluate

maintenance in terms of cost, philosophical principles and environmental considerations. This

tripartite approach draws parallels with the generally accepted model of sustainable development

(Brundtland, 1987) and offers a potentially useful framework for evaluation of ‘sustainable’ or

‘green’ maintenance interventions.

Fig. 1: Parameters for Evaluating Maintenance Interventions for Historic Buildings

The Venn diagram in figure 1 represents the traditionally accepted model of sustainability with

environmental, societal and economic factors, overlaid with the three factors that influence

maintenance for historic buildings, namely; environment, cost and philosophy. Those

interventions that intersect with all three aspects would potentially be considered as being the

most sustainable.

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To evaluate the long term maintenance requirements of historic buildings in relation to the

tripartite approach proposed for ‘green’ maintenance, it is therefore necessary to understand the

cumulative effect of routine maintenance operations in terms of not only cost and philosophy, but

also environmental impact. The proposed evaluation framework has the potential to allow

selection of maintenance options that provide a sustainable solution.

3. Maintenance and its impact upon carbon and energy use

Existing buildings have an important role to play in the reduction of carbon emissions and energy

consumption to meet global targets such as the Scottish Government’s commitment to reduce

greenhouse gas emissions in Scotland by 80% in 2050 (Scottish Government, 2009). Hammond

& Jones (2008a:96) state that the “UK construction industry consumes over 420 Mt of materials,

8Mt of oil and releases over 29 Mt of carbon dioxide annually, including a significant quantity of

new materials disposed of as waste”. A sizeable proportion of this is attributed to repair and

maintenance of existing buildings. However, resources associated with maintenance are far less

than those required to create a new building. The National Trust for Scotland (NTS) suggests that

‘the greenest building is the one that is already built’ (NTS, 2005:1), referring to the resources

already depleted for its construction which will negate the need for using further resources from

the ground. The focus of efforts to reduce carbon emissions from existing buildings appears to be

on their improvement by reducing heat loss, conserving energy and using more renewable sources

of energy (EU, 2010). ‘For existing buildings, it is clear that we cannot make them completely net

zero carbon, but the target is to reduce their carbon emissions steadily and consistently…’

(Scottish Building Standards Agency, 2007:19). While this view is vital for the overall reduction

in carbon emissions, very little work has focused on the carbon and energy associated with the

maintenance processes needed simply to retain buildings in service condition.

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Energy use and carbon emissions associated with maintenance can be distinguished into firstly,

the maintenance interventions, and secondly, the operational energy use linked to the

improvement in performance or slowing the degradation of a building.

3.1 Maintenance Interventions

Maintenance interventions clearly expend energy. All maintenance has environmental impact

with some interventions leading to higher energy and CO2 expenditure than others (Historic

Scotland, 2008). Measurement of the carbon emissions by Life Cycle Assessment (LCA) is the

determination of environmental impacts of products, buildings or other services throughout their

lives (ISO, 2006). This includes evaluation of processes or systems encompassing the extraction

and processing of raw materials; manufacturing; transportation and distribution; use; reuse;

maintenance; recycling and final disposal (Consoli et al., 1993). SBA (2009) developed a model

for a building life cycle assessment indicating 3 distinct life cycle stages (figure 2). The

‘Maintenance, repair and refurbishment’ category of the ‘Use’ stage encapsulates all aspects of

the ‘Product’; and ‘Construction’ stages. The conceptual model for green maintenance focuses on

this area in order to understand the potential for reducing energy use and CO2 emissions.

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Fig. 2: Building Life Cycle stages (after SBA 2009)

Ideally measurement of carbon associated with maintenance would extend from the extraction of

raw materials until the end of the product’s lifetime (including manufacturing, transport, capital

equipment, maintenance, disposal etc…). This is known as ‘Cradle-to-Grave’ analysis, which has

been shown to have a high degree of inaccuracy, due to the large number of variables. In order to

reduce this inaccuracy it has become common practice to specify the embodied energy of

individual materials using ‘Cradle-to- Site’ analysis (Hammond and Jones, 2008b). This approach

includes all of the energy consumed until the product has reached the point of use (i.e. building

site). Crishna et al. (2011) used a ‘Cradle-to-Site’approach to evaluate dimension stone as a

building material and demonstrated the overwhelming significance of transport leading to a vast

difference in carbon emissions depending upon where the stone is sourced. For use in the UK,

sandstone from China had over six times more embodied carbon than the equivalent material

sourced locally. This reinforces the influence of regional materials procurement on the total

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carbon associated within the construction process. Use of the five phases of the ‘Before use’ stage

in the SBA life cycle assessment (fig. 2) will develop a better understanding of carbon associated

with maintenance processes. This essentially represents a ‘Cradle-to-Site’approach.

An important component of maintenance of historic buildings is stone fabric repairs. The three

most common types of repairs for natural stone masonry are: replacement stone, plastic repair,

and pinning and consolidation. Replacement stone is considered very durable when using a

suitably matched stone that is compatible with the underlying substrate (Hyslop 2004). The

philosophical defensibility is generally good and enables the continuity of aesthetic integrity to be

achieved while simultaneously sustaining a workforce of traditionally trained, craft based

operatives (Forster, 2010a; 2010b). Good repairs of this nature use lime mortars and grouting

techniques to ‘fix’ the stone in position (fig. 3). The energy utilised in this process is potentially

considerable as a result of quarry extraction, processing and transportation. However, the life

expectancy of these repairs is good, with one hundred years being a minimal value before

replacement. Replacing natural stone could be considered an unnecessarily intrusive approach as

the preparation requires the removal of potentially sound stone to a depth of approximately

100mm. The alternative approaches of plastic repair or pinning and consolidation are intrinsically

less intrusive.

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Fig. 3: Replacement stone

Plastic repairs are a surface repair to deteriorated masonry faces (fig. 4). The term ‘plastic’ relates

to the plasticity of the materials in application and does not imply that the material contains

polymers (Ashurst and Ashurst, 1988). Deteriorated and friable stone is cut-back until a sound

surface is achieved and then lime-based mortars are used to resurface the stone. Philosophically

these repairs are highly defensible, as they enable the retention of the maximum amount of

existing natural stone, and are in most cases clearly distinguishable from the surrounding host

masonry. The ability to distinguish these repairs can also be viewed as being honest, as no

confusion will prevail when attempts are made to determine old from new fabric (Forster, 2010a).

Plastic repairs undertaken with lime as a binder and a well graded aggregate have the advantages

of flexibility, breathability and compatibility with substrate compared to inappropriate cement

based repairs (Banfill and Forster, 1999). Additionally, lime mortars are well known for their

ability to sequester carbon to ensure their set propagation (Lawrence, 2006). This capability gives

the material better environmental credentials when compared to Portland cement-based

alternatives. The life expectancy of these repairs is generally in the region of thirty years.

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Fig. 4: Plastic repair shown to bottom left, new replacement stone to right

Consolidation and pinning is a technique that stabilises deteriorating masonry, and is

philosophically highly defensible, as it retains the maximum amount of existing stone. Nylon or

stainless steel dowels are inserted into holes that are drilled into delaminating layers or detached

sections of masonry and are fixed in place with modified lime grouts (fig. 5). As the original

fabric is saved they also enable the aesthetic integrity and historic patina to be retained. These

repairs do not utilise a great deal of energy when compared to the former interventions, but their

life expectancy may be low. Additionally they can be quite costly to execute due to the labour

intensive nature of the process.

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Fig. 5: Pinning and consolidation of stone masonry

While this work focuses upon masonry repairs for traditionally built structures any maintenance

process could be evaluated using the proposed framework. The selection process for maintenance

of, and repairs to natural stone is clearly a function of philosophical defensibility, cost, durability

and energy expended. In order to evaluate energy expended and the resulting carbon emissions, a

full analysis using a life cycle approach following the SBA model is necessary. This will enable a

better understanding of the environmental impact of maintenance.

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3.2 Operational Energy Use

Maintenance has a complex relationship with carbon emissions linked to subtle changes to the

building fabric that occur as a result of maintenance. Maintenance primarily aims to retain the

functional state of a building and does not necessarily set out to improve the performance of the

building. However, certain aspects of the degradation of a building can relate to higher energy

requirements: Gaps in masonry (particularly missing mortar) lead to higher air permeability and

associated heat loss; Saturated masonry leads to reduced thermal performance through altered

conductivity of the material; Dampness may require dehumidification. All relate to potentially

higher energy consumption. Therefore some maintenance interventions can reduce or retard the

rising energy consumption associated with a degrading building. The measurement of these

complicated issues adds further to the difficulty in evaluating the energy associated with

maintenance. As stated earlier a ‘Cradle-to-Grave’ analysis, has a high degree of inaccuracy, but

presents a methodology to evaluate the impact of maintenance over the lifespan of a building.

This work does not model the magnitude of impact on carbon emissions in this context. It does

however recognize the role of maintenance in preventing rising energy costs associated with

deteriorating building conditions. It is interesting to note that although legislation to control

carbon emissions has been established in many countries, no specific guidelines are directly

targeted to reduce carbon emissions in historic buildings.

4. “Green Maintenance” Concept and Methodology

There is clearly a relationship between the number, type and longevity of maintenance

interventions undertaken, and the embodied energy and CO2 expended in repairs. A durable

repair requiring fewer repeat interventions may incur less energy over the life span of the building

than a less durable alternative. Obviously, for this concept to be of rational use the initial energy

consumption of the repairs would have to be evaluated using comparable, reproducible methods.

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Although replacing natural stone is a significantly more durable repair than a plastic repair, the

energy associated with the stone replacement is a great deal higher than the aforementioned.

Therefore to understand the energy and carbon associated with maintenance a multi-criteria

approach is required. Evaluating carbon emissions following the five phases of the ‘Before Use’

stage of the SBA model (fig. 2) results in greater reliability of the assessment of environmental

impact.

The longevity of building materials is evaluated by service life predictions. The definition of the

‘service life’ of a building is complex due to various factors, but Balaras et al. (2005:516) define

it as ‘the period of time, post installation, during which all products or materials fail, achieve, or

exceed the minimum acceptable performance’. Clearly, inconsistent data on durability of product

or materials makes the determination and bench marking of component life difficult (Balaras et

al., 2005) and leads to some Estimated Service Life (ESL) predictions being quite unrealistic. In

the case of natural stone masonry, an average life expectancy of 100 years does not take account

of a well maintained building (BCIS, 2009) or the vast differences between stone types. There are

many examples of stone still functioning satisfactorily in buildings that are several hundred years

old. The evaluation of longevity of building components appears to be ill-defined and

inconclusive (Ashworth, 1996; Douglas, 1994) as databases are inaccurate and inconsistent due to

discrepancies in their assessment methods and processes. These issues in turn make it difficult to

assess the carbon and energy saving implications of repairs to historic buildings.

The time between interventions is influenced by many variables, including material durability;

degree of exposure; building detailing; quality of repair and specification. Undertaking repairs at

frequent intervals increases the risk of mechanical damage to the masonry associated with

scaffolding. Less regular masonry repair can reduce the risk of this damage and also, aligns with

the philosophical principle of least intervention.

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Figure 6 diagrammatically illustrates the implications of undertaking maintenance interventions

on the service condition of masonry over time. The downward sloping lines signify the steady

decline in condition over the life of the masonry repairs. Each maintenance intervention brings

the area of masonry back to optimal service condition. It then deteriorates at a rate that depends

on the repair type. Intervention is assumed to occur when the minimum acceptable condition is

reached, and the saw tooth profile results from successive interventions, each extending the life of

the masonry. A steep gradient denotes a repair with short life expectancy, such as pinning and

consolidation, which can extend the service condition by 20 years. Conversely, a shallow gradient

equates to a durable long lasting intervention, such as masonry replacement lasting at least 100

years.

Fig. 6: Impact of maintenance interventions on the service condition over the whole life of a

building.

If the interventions are considered in terms of carbon emissions it becomes possible to model the

whole life cycle of a building in terms of the carbon associated with not only constructing the

building but also maintaining it over its life span. Figure 7 overlays the carbon emissions for each

maintenance intervention on the service condition graph. Each intervention is characterised by its

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longevity and embodied carbon. The model distinguishes between ‘brown’ and ‘green’

maintenance, i.e. those interventions of high and low carbon impact. The cumulative effect of

‘brown’ maintenance increases the total carbon expended far more quickly than ‘green’

maintenance. In this context, brown maintenance is synonymous with interventions that have

poor longevity and higher embodied energy, whilst green maintenance is associated with repairs

that have high longevity and low embodied energy.

In principle, the more frequent the maintenance intervention, the higher the embodied CO2, but

various mechanisms may exist to reduce the total CO2 expended, such as locally sourcing

materials, using regional companies to undertake the work and selecting alternative repair

solutions. A ‘Cradle-to Site’ approach is required to fully account for CO2 associated with all

aspects of the repair to fully appreciate its environmental impact. On the face of it an intervention

with low carbon emissions has less environmental impact. However, the complexity of life span

and combinations of repair types, suggests a whole life cycle approach is necessary in

determining ‘brown’ from ‘green’ maintenance.

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Fig. 7: Relationship between longevity of repair and total cumulative carbon expended

If we evaluate the efficacy of repairs in terms of CO2 expenditure, then the type of repair selected

could be tailored to suit environmental aspects rather than longevity alone. This practical

approach may be welcomed as society moves towards a low carbon economy and ‘green’

procurement selects and prioritises materials with low embodied energy. Additionally, as carbon

trading becomes more prevalent this method of evaluation can be converted into a supplementary

financial cost. Philosophical aspects of maintenance are essentially subjective, but are an integral

component of achieving ‘good conservation’. Retention of existing masonry fabric best satisfies

philosophical tenets, however, it is inevitable that masonry will require intervention at some

stage. Good quality, durable materials and well executed craft based techniques offer

philosophically defensible interventions.

Figure 8 shows how the ‘Environmental Maintenance Impact’ (EMI) builds up. This is the

cumulative effect of maintenance interventions over the masonry’s life denoted in this case by n1,

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n2, n3… Each intervention has a carbon impact (ce) and a longevity (l). The total carbon

expended by maintenance interventions is illustrated by equation 1.

Fig. 8: Determination of theoretical ‘Environmental Maintenance Impact’ (EMI) of

interventions

Carbon expended on maintenance

n

i

ice1

(1)

where;

n = number of interventions

ceI = carbon expenditure for the ith intervention [evaluated by using ‘Cradle-to-Site’ tools]

[CO2/Kg]

If we include the initial state of the masonry in the form of its total embodied carbon (CO2op), the

total carbon after the nth intervention is given by equation 2. The total carbon embodied in the

structure is that from the ‘Before use’ stage in figure 2, while the carbon expended in the repairs

defined in ‘Maintenance, repair and refurbishment’ stage in figure 2.

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Total embodied carbon + carbon expended = CO2op +

n

i

ice1

(2)

Equation 2 correlates with the steps associated with the maintenance interventions shown in

figure 7, and assumes that all the repairs are immediately replaced once their life expectancy has

been reached. By adding the total embodied carbon for maintenance interventions to that of the

masonry fabric we can determine the total embodied carbon for the masonry at any point over its

life span.

6. Testing the Model

To test the model the functional unit of repair is defined as a square metre of façade. Four repair

scenarios are defined for the maintenance of a square metre area of delaminated stone masonry

over a study period of 100 years (figure 9). Certain combinations of masonry repair are more

common than others i.e. pinning and consolidation would be done only once and then followed

by stone replacement. It would be highly unusual to pin and consolidate a plastic repair.

Scenario 1: Replace in natural stone

Replacing the defective material with natural stone is assumed to require the cutting back of

approximately 100mm of the defective material and building in a new section of stone. The life

expectancy is taken to be 100 years and all of the replacement stone’s EMI is attributed to the

study period.

Scenario 2: Pinning and consolidation, followed by stone replacement

Pinning and consolidation of the masonry is assumed to require high grade threaded stainless

steel dowels 75mm long and 6mm diameter, inserted at approximately 200mm spacing and

should ensure the survival of the historic fabric for an initial 20 year period. After this point the

repair may fail and require further intervention in the form of replacement stone. As previously

mentioned this process requires the ‘cutting out’ of the defective masonry to a depth of

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approximately 100mm and building in a new section of stone. The replacement stone will last

beyond the 100 year study period and so only 0.8 of its EMI is attributed to the study period.

Scenario 3: Repeated plastic repair

The delaminated surface of the masonry is assumed to be cut back to a point at which sound

substrate is reached and lime based mortar used to resurface the stone. The repair depth is

assumed to be 30 mm and the intervention is reapplied every 30 years (3.33 times in the study

period).

Scenario 4: Single plastic repair followed by stone replacement

In contrast to scenario 3, if deterioration has occurred to the substrate forming the base of the

plastic repair it is necessary to further cut back the natural stone. This will prevent repeated

plastic repairs due to build up of excessive thickness. In this situation the plastic repair and the

decayed natural stone is assumed to be removed after 30 years and new stone built in to a depth

of 100 mm. As with scenario 2 the replacement stone will last beyond the 100 year study period

so only 0.7 of its EMI is attributed to the study period.

Fig. 9: Repair scenarios

Three organisations entrusted with the repair and maintenance of traditional buildings - Historic

Scotland, National Trust for Scotland and City of Edinburgh Council - gave access to their

maintenance records for masonry buildings. A detailed evaluation will be reported later but the

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data confirmed the validity of the assumed lifetimes of the four repair scenarios, for the same

location, Edinburgh. Table 1 summarises the EMI, evaluated in terms of embodied CO2

expenditure, over the 100 year study period, for each scenario. In each scenario the EMI is

calculated from data relating to the average embodied carbon associated with the repair of a 1m2

area of masonry, determined on a ‘Cradle-to-Site’ basis including both materials and transport.

Table 1: Carbon emissions associated with alternative repair scenarios undertaken on one

square metre of masonry wall

Scenario 1 Scenario 2 Scenario 3 Scenario 4

Stone

replacement kgCO2e/m

2 36.4 36.4 - 36.4

Number of

interventions 1 0.8 - 0.7

Pinning and

consolidation kgCO2e/m

2 - 13.9 - -

Number of

interventions - 1 - -

Plastic repair kgCO2e/m2 - - 15.1 15.1

Number of

interventions - - 3.33 1

Total EMI kgCO2e/m2 36.4 43.0 50.3 40.6

*Materials data derived from: Crishna et al 2011; Hammond and Jones, 2008a, 2008b, Transport data

derived from Defra, 2009; IFEU, 2008.

From the data shown in table 1, it is evident that, of the individual interventions, stone

replacement has the highest initial embodied CO2. However when this is placed in context of a

100 year maintenance profile it has the lowest EMI because of the short life expectancy of the

other interventions. In particular, repeated plastic repair turns out to have a nearly 40% higher

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EMI over 100 years than replacement stone. Additionally, the transport of materials has a major

impact on the results, as was noted by Crishna et al (2011), and accounts for approximately a

quarter of the EMIs reported in table 1. Therefore the use of durable, locally sourced materials

should be encouraged. The implication of this approach is that ‘green’ procurement is one

significant mechanism to reduce the CO2 associated with the repair. The implementation of this

model will enable comparative analysis to be undertaken on similar buildings from various

organisations, within the same region. This novel method for viewing and evaluating maintenance

for buildings, shifts the emphasis away from cost towards embodied CO2 retention within the

fabric, and CO2 expenditure on the maintenance interventions. It focuses on how ‘green’ the

maintenance works are. This concept also indirectly helps support the conservation needs of the

historic building fabric as it may encourage a minimal intervention based approach to

maintenance.

7. Discussion and Conclusion

While there is an international consensus on the philosophy of historic building conservation,

which recognises the importance of maintenance as a positive benefit, maintenance is a neglected

issue in many countries. This paper has proposed that significant reductions in CO2 and energy

can be achieved by ‘Green Maintenance’, which could be of value to those making decisions for

repair and maintenance. It also indicates the importance of procurement strategies and longevity

of repairs.

The development of the formulaic expression for green maintenance will enable those entrusted

with repair selection to make rational decisions relating to CO2 expenditure and durability. The

data utilised to test the model should become more rigorous with time as LCA and life

expectancy information becomes more widely available, for a greater number of products. It is

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the authors’ view that this approach should be adopted by large organisations responsible for

maintaining and repairing buildings both historic and modern.

Recognising the need to overlay the environmental outcome with an evaluation of philosophical

defensibility, a well founded intervention may not necessarily correlate with low CO2

expenditure. This framework facilitates a deeper analysis of the tensions between philosophy of

repair, set against carbon emissions and cost. For example, the pinning, dowelling and

consolidation of a deteriorating piece of natural stone may be highly defensible in terms of

minimal intervention, whilst simultaneously being good in terms of CO2 and cost expenditure in

executing the repair. However, over the equivalent lifespan of a building there is higher carbon

associated with this approach than associated with stone replacement. When philosophical

decisions are set within the context of carbon emissions and cost, initially difficult decisions can

be easier to defend.

As previously mentioned, embodied carbon and energy analysis appears to be problematic as in

practice it has many complications. Hammond & Jones (2008a) claim that, the analysis carries a

natural level of variation, and methodological differences in calculations, boundary conditions

restriction and general incorrect assumptions (Hammond & Jones, 2008a). The next stage of the

work will involve large scale testing of the model using the maintenance records provided by the

three industrial collaborators, using ‘Cradle-to-Site’ assessment and life-cycle inventory analysis

tools. Internationally the development of the model requires local data to evolve the

understanding of carbon emissions associated with local materials and processes. This will enable

a greater understanding of the implications of maintenance interventions in different international

and regional settings.

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8. Acknowledgements

The authors would like to thank the contribution made by the National Trust for Scotland,

Historic Scotland and the City of Edinburgh Council for access to maintenance and repair data.

9. References

Arup (2003) Maintaining Value-Module 5: Demand and Supply, Building the Business Case for

Planned Maintenance, Arup Research + Development, London.

Ashurst, J. & Ashurst, N. (1988) Practical Building Conservation: Stone Masonry (Volume 1),

Gower Technical Press Ltd, Aldershot.

Ashworth, A. (1996) Estimating the Life Expectancies of Building Components in Life-Cycle

Costing Calculations. Structural Survey, 14 (2), 4-8.

Balaras, C.A., Droutsa, K., Dascalaki, E. & Kontoyiannidis, S. (2005) Deterioration of European

apartment buildings. Energy and Buildings, 37(5), 515-527.

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