Sustainability of Biomaterials in
Construction
understanding the issues for products using plant - and animal-based materials
by Dr Jo Mundy
with contributions from John Hutchinson, Dr Gary Newman and Mark Lynn
Overview
As pressure on resources grows and the
demand for sustainability rises, much
attention is being given to the use of
materials from plants and animals as the
basis for a wide range of products. However,
it is extremely difficult to get a clear picture
of the consequences of using such
'biomaterials' as alternatives to existing
(typically non-biological) options.
This paper is aimed at manufacturers
interested in manufacturing with these
products and those interested in selecting
them. It is also of interest to those producing
policy relating to these materials and
researchers seeking to assess them.
Contents
Overview ....................................................................................................................
1
Background ..................................................................................................... 1
2
Commercial issues ........................................................................................... 2
2.1
Production and procurement ................................................................ 2
2.2
Standards ............................................................................................. 2
2.3
Economic issues ................................................................................... 3
2.4
Practical issues ..................................................................................... 3
3
Social issues .................................................................................................... 4
4
Environmental performance issues................................................................... 4
4.1
Environmental problems related to agricultural systems ........................ 5
4.2
Methodological problems for agricultural LCAs ..................................... 5
5
Conclusions ................................................................................................... 15
6
References .................................................................................................... 15
The paper reviews the key economic, social
and environmental issues for biomaterials and the approaches being taken to address them. It
highlights the need to ensure that these materials are assessed in a way that is comparable to
approaches being used to assess existing materials that are performing the same function.
Sustainability of Biomaterials in Construction
1
Background
Biomaterials have a long history of use as construction materials, such as timber for framing, boarding
and roofing, and reeds and straw for roofing and flooring. Where the use of these materials is well
established and their performance known then they continue to be used for these applications.
However, where such materials are used in novel applications or novel combinations, or both, then
there may be resistance to their uptake unless their performance in practical, economic and
environmental terms can be demonstrated.
Biomaterials present us with the opportunity to capture and exploit properties that have evolved in
nature to provide certain performance characteristics. Biomaterials have the potential to provide
construction materials with the following benefits:
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Capture and storage of carbon extracted from atmospheric CO2 by recent photosynthesis
Sustainable production as crops grown annually or as longer harvest-cycle forest.
Biodegradability at end of life. (Controlled decay inside an anaerobic digester would produce
both organic fertiliser and bio-methane to supply energy)
Low or almost zero linear coefficients of thermal expansion
The property of controlling temperature and humidity in enclosed spaces by phase changes of
water in cells
High vapour diffusivity and 'Fickian' vapour dispersal
Usually high specific heat capacity
Low thermal diffusivity
Often good performance-to-weight ratios
Lower embodied energy.
Achieving lower embodied energy requires us to minimise the processes and materials, such as
coupling agents, synthetic glues, biocides, preservatives and fire-retardants, used to produce the final
product. The more we are able to deploy nature's answers to adhesion and preservation, the less we will
need to use man-made alternatives.
A key question in the development of biomaterials is: "Should we work with a biomaterial's inherent
properties or should we process it to produce a different structure and achieve a different
performance?" A key criterion for judging this question's answers is the requirement for sustainable
development. This paper explores the economic, social and environmental issues that should be
assessed when seeking to evaluate the sustainability of biomaterial products.
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Sustainability of Biomaterials in Construction
2
Commercial issues
2.1 Production and procurement
Many applications of bio-based materials in construction are relatively new and the market structure
characterised by a low concentration of SMEs that are making the transition to a more mainstream
model. These business models are currently operating in the UK:
a) Direct manufacture
i.
Small scale running of high capacity equipment - operating plants sub-optimally is likely
to result in more inputs per unit of production and so increase the environmental
burden of associated with each unit of production. However, when demand eventually
meets capacity, reduced unit impacts may be achieved via the effects of scale and
specialised production equipment.
ii.
Small scale production using low capacity equipment - this may offer a lower impact
model particularly if local materials are sourced and sold locally for products with
relatively little processing or additional materials. However, energy and other
environmental impacts may be greater for certain materials when processing methods
are applied on a very small scale. This appears to be the case for raw wool scouring for
instance.
b) Utilise existing UK capacity - the use of spare capacity in complimentary industries within the UK
to produce bio-based materials for construction. This enables the biomaterial company to
benefit from scale economies and associated environmental benefits from an earlier stage. In
the medium term, sharing capacity may not be the most efficient way of minimising
environmental impacts or maximising the impact of specialisation. This approach reduces the
impact of building new capacity in the short term and can allow for an efficient transition from
small to large scale dedicated production.
c) Import and distribute - the importing and distribution of biomaterials from established overseas
markets such as Germany. The biomaterial company can benefit from established scale
economies and potentially better social and environmental standards of production. Certain
bio-based materials such as hemp and flax are not widely available in the UK so sourcing these
types of material from overseas provides a way of utilising these crops from areas where they
are abundant. However, the energy-related impacts will depend on the energy mix of the
country of origin plus there are additional transport impacts, particularly important for low
density finished goods.
2.2
Standards
The nascent state of the segment means there are few standards that embrace the sector and the
various product groups within. As such products can fail to meet the expectations of specifiers. This can
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Sustainability of Biomaterials in Construction
be addressed through technical approvals such as British Board of Agrément (BBA) certification or the
European Technical Approval (ETA) for established products such as insulation. However, it can prove
more difficult for newer or novel applications to gain standard recognition.
The different inherent properties of bio-based materials can also make standardised tests derived for
synthetic products difficult to apply and can affect the results. For example, 'hot-box' measurement of
thermal conductivity of sheep's wool generates anomalous variation in the lambda value. The initial
result is very good. It can be as low as 0.029 Wm-1K-1 for a densely woven textile or mat. The value then
increases steadily as heat continues to be applied. Most quoted lambda values for wool are around
0.035 Wm-1K-1; good, but not as good as the best synthetic insulations. It is not clear if this effect is
caused by the hygrothermal properties of the sheep's wool.
2.3
Economic issues
The economics of non-timber biomaterial supply is greatly influence by local and national agricultural
policy. In the case of UK sheep’s wool, all wool must be purchased through the British Wool Marketing
Board (BWMB) scheme, which can result in a great disparity between the final processed cost of fibre
compared to the farm gate price. The nature of the BWMB scheme can also cause large fluctuations in
raw material costs that can affect stable finished goods prices. Similarly, the availability and cost of
crop fibres such as hemp or flax can be influenced by agricultural subsidies and opportunity costs
associated with demand for other crops. The availability of hemp recently has been strongly affected by
the downturn in the automotive sector, since this is a key sector for hemp and a strong driver for its
production. Climate and seasonality factors can also introduce additional uncertainties. All of these
factors create a relatively complex supply chain which ultimately contributes to the cost of finished
goods.
2.4
Practical issues
As with other production processes using input materials that are inherently variable, producing
biomaterials with consistent physical or mechanical properties can be a challenge. The producer is also
subject to seasonal availability issues and the influence of the climate prevailing during the growing
period on the quality of the input material and ultimately on the performance of the final product.
Biomaterials have additional properties that are less widely understood and often more difficult to
quantify such their hygroscopic and hygrothermal properties. Natural fibres are capable of binding
between 25% and 40% of their weight in moisture meaning they can act as buffers or sinks for moisture
within certain building structures. The ability of natural fibres to bind moisture leads to greater
hygrothermal stability which can be an important property for certain applications such as thermal
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Sustainability of Biomaterials in Construction
insulation where the insulation performance can be greatly influence by the presence of free moisture.
This ability to take up moisture also influences their potential durability and service life.
There are also practical issues to be addressed during the life of these materials; their performance in
use is highly influenced by whether appropriate design decisions were taken to incorporate them into
the building to achieve their potential service life.
3
Social issues
Environmental and social issues surrounding the supply of bio materials have been well recognised in
the field of forestry and sustainable forest management schemes, such as the schemes of the Forest
Stewardship Council and the Pan European Forestry Council, have been developed to help assess this
aspect. Whereas these may represent more extreme aspects, they highlight the importance of
responsible sourcing to the biomaterials sector. Sourced and utilised responsibly, biomaterials offer
the opportunity to utilise highly sustainable material sources in a variety of end-uses and to contribute
to the sustainability goals of the construction sector as a whole.
Biomaterials in construction also face the same issues as the biofuels sector, as described in the
Gallagher Review, the key ones being the potential displacement of food crops and the Climate Change
impacts of changing land use. It is also possible that biomaterials will come under pressure in the area
of water consumption as supplies of fresh water come under ever greater stress.
4
Environmental performance issues
Agricultural systems raise particularly complex issues for Life Cycle Assessment (LCA) methodology.
These issues include:
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Allocation between co-products (including stored carbon benefits)
The selection of agricultural reference systems
Emissions from fertilisers and biocides in the field
The origin and transport of commodity products
The handling of biogenic emissions such as N2O emissions from agricultural soils
The use and choice of a ‘reference land use’ system
The end-of-life scenario and associated assumptions (particularly the assumed proportion of
methane emitted during biodegradation).
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Sustainability of Biomaterials in Construction
4.1 Environmental problems related to agricultural systems
The following environmental problems have been identified for agricultural systems (Milà i Canals,
2003):
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Energy consumption (contributing to climate change, acid rain, resource depletion etc.)
The use of nitrates and phosphates (causing pollution of surface- and groundwater)
Agri-chemical use (resulting in toxicity impacts)
Reducing soil quality (producing soil degradation, pollution, erosion etc.)
Water depletion
Decrease of biodiversity due to prevalence of mono-culture.
4.2 Methodological problems for agricultural LCAs
These relate to:
1. Method choice
2. Goal definition and functional unit
3. Inventory analysis
i.
Boundaries
ii.
Processes included and capital goods
iii.
Substance flows to and from soil
iv.
Choice of data sources with respect to the study’s goal
v.
Location of nutrient emissions
vi.
Groundwater abstraction and link with desiccation
vii.
Allocation
viii.
Crop rotation
4. Classification and Characterisation
5. Sustainability indicators
6. End of life
4.2.1 Method choice
LCA was developed to be location-independent (Wegener Sleeswijk et al., 1996). However, in
agriculture, differences in local conditions, such as soil type and climate, may influence the
environmental impacts resulting from a given emission. Inventory data may be very dependent upon
local conditions; site-dependent aspects might have a greater influence on an agricultural LCA’s results
than activity-dependent aspects.
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Sustainability of Biomaterials in Construction
4.2.2 Goal definition and functional unit
Most agricultural LCAs are aimed at assessing the impacts of producing foods; agricultural systems are
typically multi-functional (Milà i Canals, 2003); they can be related to keeping the land to a definite
appearance as well as to the production of products.
The functional unit for non-food crops (whether wholly non-food, e.g. hemp, or partially as the nonfood part of a food crop, e.g. wheat straw) can also be faced with the complication of multiple functions
from the system. However, the purpose of the non-food product will guide the selection of the
functional unit. A study may produce a ‘delivered unit’ rather than a functional unit, with the delivered
unit being an amount of the non-food crop material typically from cradle-to-farm (or factory) gate.
4.2.3 Inventory Analysis
The main Life Cycle Inventory Assessment (LCIA) topic in reported agricultural LCA studies appears to
be the need to develop new impact categories addressing the impacts caused by agricultural systems.
The issues of land use, land quality and biodiversity have received particular attention.
Three aspects related to agricultural land use have been highlighted (Cowell and Clift, 1997): actual or
potential productivity of land; effects on biodiversity, and aesthetic value of landscapes. Soil quality
and generic land quality indicators have been studied by many to assess the impacts on potential
productivity of land. The following have been suggested Mattsson et al. (2000) as useful indicators of
long-term soil fertility and biodiversity: soil erosion, soil organic matter, soil structure, soil pH,
phosphorus and potassium status of the soil, and the impact on biodiversity. However, they
acknowledge that these indicators are a mix of quantitative and qualitative and difficult to aggregate.
Biodiversity indicators have been researched by many and the Hemeroby concept explored (see
Brentrup et al. (2002) for a review), which considers a classification scheme for land based on its
‘naturalness’.
However, there is no single definition of land use; some researchers exclude landscape effects, others
distinguish between the impacts of occupation and ecosystem impacts that change the time needed
for the ecosystem to return to its natural state. There is general consensus that land use covers any
human activity requiring land to carry it out.
4.2.4 Boundaries
Since there are no factory walls it can be difficult to answer the question, “where does the agricultural
system border the environment system?”
How the soil is regarded can have a considerable influence on the final results: some have argued for its
exclusion but others regard it as an ancillary product that is required by the system and altered by it,
even though it does not remain part of the final product. The alteration of the soil by the agricultural
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Sustainability of Biomaterials in Construction
system introduces a time boundary consideration as it has implications for future activities - this is
covered in the section on crop rotation.
Cowell (1998) raised the question of time boundaries and suggested that activities in the past affecting
actual productivity should also be included in the analysis. Examples of such activities are fertiliser use
that is useful for more than one crop, hedge establishment and maintenance etc. Therefore, the system
under study should include all these relevant activities, and so comprise full crop rotations, whole forest
rotations, etc.
Accounting for crop rotations is addressed in a subsequent section.
Taking time into account for forest-based products presents practical problems in that a forest stand
ready for harvest now in the UK was planted 70 to 100 years ago, and little or no information is available
on the practices applied to that stand to establish and maintain it. It is also true that a stand planted
now will have known establishment practices but its future management, whilst planned now, is likely
to vary over its 70- to 100-year life time. Consequently, time-dependency is usually addressed by
assuming that past and future practices are the same as those used currently.
4.2.4.1 Processes to be assessed and capital goods
This presents a particular challenge - it is not practical to assess all activities relating to a product's
production and the process tree must be cut off at various points. Deciding what processes to assess
and what to exclude requires an understanding of the system and the likely impacts; many state that
the only processes that can be omitted are those that contribute scarcely if at all to the environmental
interventions associated with the functional unit – though this requires experience to assess because it
is difficult to determine how important a process is until its contribution to the whole has been
assessed.
The following list sets out the agricultural processes that should typically be included in an LCA for
agricultural products (Wegener Sleeswijk et al., 1996):
1. crop cultivation
a. fertiliser use (materials and application fuels)
b. crop protection (materials and application fuels)
c. soil tillage (application fuels)
d. irrigation (extraction and application fuels)
e. sowing (materials and application fuels)
f. harvesting (application fuels and organic waste disposal)
g. capital goods: production and maintenance of machinery, farm tracks and roads and
buildings.
2. livestock breeding
a. feeding (materials and application fuels)
b. care (materials and application fuels)
c. manure-related activities (materials , treatment and application fuels, and waste
manure disposal)
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Sustainability of Biomaterials in Construction
d. shed maintenance (materials, application fuels, and waste disposal)
e. milking (materials and machinery fuel use)
For other processes, the choice for or against inclusion can be made using ‘cut-off’ rules. The text below
has been extracted from ISO 14044 (2006) to illustrate this approach (see section 4.2.3.3.3 of ISO 14044
for more details):
Several cut-off criteria are used in LCA practice to decide which inputs are to be included in the
assessment, such as mass, energy and environmental significance. Making the initial
identification of inputs based on mass contribution alone may result in important inputs being
omitted from the study. Accordingly, energy and environmental significance should also be
used as cut-off criteria in this process.
a) Mass: an appropriate decision, when using mass as a criterion, would require the inclusion in
the study of all inputs that cumulatively contribute more than a defined percentage to the mass
input of the product system being modelled.
b) Energy: similarly, an appropriate decision, when using energy as a criterion, would require
the inclusion in the study of those inputs that cumulatively contribute more than a defined
percentage of the product system’s energy inputs.
c) Environmental significance: decisions on cut-off criteria should be made to include
inputs that contribute more than an additional defined amount of the estimated quantity of
individual data of the product system that are specially selected because of environmental
relevance.
EN 15804 (2012) has been developed as a means of harmonising the approach to producing EPD for
construction products. En 15804 adopts this approach and specifies a cut-off of 5% for energy and
mass.
In practice, capital goods are often not considered in an LCA, because their contribution to the
aggregate environmental score of a product unit or functional unit is deemed negligible (there is also
the practical consideration that there is often insufficient time to evaluate the contribution from capital
goods). However, it can be argued that machinery and infrastructure are often used less efficiently in
agricultural systems than in industrial systems, and that the allocation of their production to the
functional unit is usually relevant (Cowell and Clift, 1997).
Another reason for omitting capital goods from an LCA is that there is frequently little difference in
their use between two comparable product systems. For agriculture, if per-hectare yields differ then
this assumption is wrong.
Agricultural and forestry activities employ a number of capital goods with relatively short service lives,
e.g. combine harvesters and harvester-forwarders, and a number of capital goods that require relatively
8
Sustainability of Biomaterials in Construction
large amounts of material, e.g. farm or forest tracks and roads. The omission of machinery or
infrastructure may have a relatively large influence on the final result. The environmental interventions
associated with the production and maintenance of machinery therefore needs to be included in an LCA
for agricultural products. Similarly, the contribution of infrastructure should not simply be ignored.
However, farm buildings can generally be omitted from the study, except in the case of greenhouse
horticulture and in studies where farm buildings are the main source of differences between systems.
4.2.4.2 Substance flows to and from soil
If the soil is included in the LCA then all inputs to the soil such as fertiliser and manure should in
principle be classified as causing Eutrophication (i.e. nutrifying). Besides emissions of minerals and
other substances to the soil, agriculture also involves extraction of these substances from the soil. In
the inventory phase of an LCA, the quantity of a substance extracted from the soil should be subtracted
from the quantity emitted to the soil, because the extracted substance held in the crop has no
environmental impact. This is particularly relevant for substances present in fertiliser dressings.
It has been proposed that a soil mineral balance should be used to determine what fraction of the
applied mineral supplements end up in the environment (Wegener Sleeswijk et al., 1996). This balance
can be used to calculate the emission, by subtracting all outputs from all inputs. For annual crops, e.g.
most arable crops, the long-term equilibrium situation can be taken as the point of departure; i.e. it is
assumed that, on balance, there is no accumulation of nitrogen. The excess nitrogen is then divided
over volatilisation, run-off, leaching and denitrification – the Intergovernmental Panel on Climate
Change (IPCC) have derived approaches for calculating in-field losses associated with synthetic and
organic fertilisers. However, in the case of perennial or long-term crops, such as grass or trees, the
assumption of no long-term accumulation of nitrogen is no longer valid, and accumulation should be
included in the balance. For phosphorus a similar but simpler balance can be drawn up but there is
accumulation in the soil. The excess phosphorus is divided over leaching, run-off and accumulation.
A similar balance should also be drawn up for other substances added to the soil, such as heavy metals.
Soil-free production, such as substrate cropping, does not require a soil mineral balance.
4.2.4.3 Choice of data sources with respect to the study’s goal
The agricultural sector comprises a large number of individual farm enterprises with no two farms being
identical. This means that the goal of the study should be used to guide whether it is appropriate to opt
for average data, normative or representative data, or data on individual farms. With each of these
choices, but particularly in the case of average data, the spread of results due to the spread of the raw
data must be accounted for. Examples of goal-appropriate data sources are:

To investigate the environmental impacts associated with milk sold in supermarkets, average
data on milk production is appropriate
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Sustainability of Biomaterials in Construction
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To compare current milk-production methods, average data on the companies applying the
various production methods can be used
To understand which elements of an individual product (system) have the greatest bearing on
the environmental impacts, data specific to that product (system) are needed.
If the government wishes to use LCA to back up a policy to encourage or discourage a given
production method, normative data specific to companies applying the production method in
question are appropriate.
4.2.4.4 Location of nutrient emissions
It has been proposed that, contrary to conventional LCA, nutrient accumulation in the soil requires a
distinction between problem areas – where nitrification constitutes a problem, e.g. in large parts of
Western Europe – and non-problem areas – where nitrification does not form a problem (virtually the
entire 3rd World, where soil exhaustion is the problem) is needed (Wegener Sleeswijk et al,. 1996).
In areas where Eutrophication (nutrification) is not a problem, then the accumulation of minerals in the
soil should not be classified as a nutrifying emission. This means that in the inventory phase a
distinction must already be made, on the basis of the location of the emission, between areas where
nutrification is a problem and areas where it is not. Emissions of soil-supplement minerals to other
environmental media, via run-off, leaching and volatilisation, are classified as nutrifying, because these
emissions can lead to Eutrophication of surface waters or of areas in the vicinity of the non-problem
area. If it is unknown whether Eutrophication constitutes a problem in a given area, all nutrifying
emissions should be regarded as causing Eutrophication.
4.2.4.5 Groundwater abstraction and link with desiccation
LCA currently gives no consideration to desiccation, because this is considered to be a local problem. In
agriculture, however, desiccation does constitute a major environmental problem. Key determining
factors in the problem of desiccation are drainage, watertable management and groundwater
abstraction. Drainage and watertable management are highly location-specific and are difficult to
relate to a functional unit of product and therefore cannot currently be included in an LCA. Desiccation
should consequently only be included if it is governed largely by the direct or indirect withdrawal of
groundwater in the area in question.
It has been advocated that, as for Eutrophication, allowance should be made for the difference
between problem and non-problem areas. Groundwater abstraction should not be classified as
desiccating in areas where there is no desiccation problem, or in areas where groundwater abstraction
does not contribute to this problem (for example, where surface water levels are being kept artificially
low thus determining the degree of desiccation). If it is unknown whether a groundwater-abstraction
process contributes to desiccation, groundwater abstraction should be classified as desiccating.
ISO is currently working on the production of a water footprint standard (ISO 14046) that is based on
LCA.
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4.2.4.6 Allocation
Allocation is the sharing of environmental burdens between the products of a multi-output process. ISO
14041 (1998) recommends that LCA studies should:
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Avoid allocation wherever possible by dividing the shared unit process into sub-processes
Allocate on any underlying physical relationship
Allocate on a relevant relationship.
EN 15804 also advocates the avoidance of allocation wherever possible giving priority to a physical
relationship where processes can be subdivided and to a value (economic) approach when subdivision is
not possible.
As noted earlier, co-production is common in agriculture. The various parts of animals and plants
produced are often used for different applications. Before allocation is undertaken, it must therefore be
clear that multi-output processes have as far as possible been divided into single-output processes.
Only for those processes that cannot be further subdivided should allocation be carried out, and this
should be done on the basis of economic value.
If manure is used in arable farming, recycling is taking place and the environmental interventions
associated with the processes involved (storage, transport, processing) should be allocated to the
product system that pays for these processes. If payment is collective, e.g. in the case of storage in a
manure centre, interventions should be allocate on the basis of the ratio between the cost paid by the
arable farmer and the cost paid by the cattle farmer. Again, these rules are based on economic value.
The inclusion of complete rotation schemes can also present allocation issues. It has been suggested
that the inclusion of soil quality and quantity into the LCIA greatly reduces the allocation problem for
crops but this requires the development of a convenient impact indicator.
The carbon cycle also presents an allocation problem in agricultural systems. Some consider it a
negative climate change impact and account for it whereas others regard the storage as happening
over too brief a period with the CO2 released again when the material degrades. This is sensible for
food crops where the lifetime of the product is very short but it is not the case for non-food crops used
in construction products, for example, the Green Guide uses a 60-year study period for assessing
building element specifications. Consequently, CO2 sequestration is taken into account along with endof-life scenarios that include disposal in landfill where part of the sequestered carbon will be emitted as
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methane; the Global Warming Potential of methane is more than 20 times that of CO2 over a 100-year
period1.
4.2.4.7 Crop rotation
Agricultural crops are typically cultivated in a system of crop rotation, with different crops being
cultivated in succession on a given plot of land. If a comparison is being made between different croprotation schemes, this will cause no extra allocation problems. In practice though, such a comparison
will not often be useful, because LCA is a tool designed for comparing the environmental impacts of
various different products. What will usually be compared is a product from one crop-rotation scheme
with one from another rotation scheme. This gives rise to difficulties, because the various crops and the
activities performed in cultivating these crops often also have consequences for the crops grown later in
the rotation scheme. Examples include:

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Soil fumigation carried out for potatoes but also benefiting other crops
Application of organic fertilisers in a given crop, with some fraction of the minerals only being
taken up after the following crop has been sown.
These allocation problems cannot simply be ignored in an LCA. The question ‘Why is a given activity
performed?’ can be used to guide decisions. For example, the soil fumigants applied in potato
cultivation would not be used if potatoes were not included in the crop-rotation scheme. The
environmental interventions associated with the soil fumigants should therefore be allocated entirely
to the potatoes, even if benefits accrue to other crops too. In the same way, the environmental
interventions associated with the application of nitrogen fertiliser are allocated to the crop to which the
fertiliser dressing is applied, while the environmental interventions associated with application of
phosphate and potassium are divided over the crops in the rotation on the basis of the recommended
dressings for each individual crop.
It has been recommended that organic matter is allocated on the basis of the share of the various crops
in the crop rotation scheme (expressed in terms of space requirements, ha.year). When multiple
1
Climate Change impacts can be assessed for effects occurring over a 20-year, 100-year or 500-year timeframe.
The Intergovernmental Panel on Climate Change regularly reviews and updates the characterisation factors for all
greenhouse gases. The BRE methodology assesses Climate Change over the 100-year timeframe.
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fertilisers (manure and other animal wastes, in particular) are applied, the emissions occurring up until
the moment the mineral reach the soil (emissions during storage, transport and application) are divided
over the various crops on the basis of the economic value of the minerals in the fertilisers.
Given the importance of the crop-rotation scheme for further choices within an LCA, it is of major
importance that the crop-rotation scheme being used to cultivate the products in question already be
indicated in the goal definition.
4.2.5 Classification and Characterisation
LCA’s current method for the characterisation of toxic substances does not allow for environmental
transport and degradation of these substances, but for various agricultural pesticides, these processes
may be highly influential on the degree to which the toxic potential of these substances leads to
potential environmental impacts. Wegener Sleeswijk et al. (1996) derived new equivalency factors,
incorporating intermedia transport and degradation, for the most commonly used agricultural
pesticides for the toxicity themes of CML’s LCA method. These equivalency factors were calculated
with the aid of the USES (Uniform System for the Evaluation of Substances) model (RIVM, VRO, WVC,
1994). However, the new equivalency factors cannot be compared with the factors in the LCA Guide,
and the scores calculated for pesticides using these factors can only be listed separately.
The Institute for Environmental Research and Education (IERE) has derived a list of Impact Categories
for agricultural product LCAs:
Climate Change
Stratospheric Ozone Depletion
Eutrophication
Photochemical Smog
Acidification
Airborne Toxicity
Waterborne Toxicity
Water Resource Depletion
Mineral Resource Depletion
Land Use/Biodiversity
Soil Conservation
Hormone Use
Antibiotic Use
Gene Modified Organisms
Of these, Land Use/Biodiversity, Soil Conservation, Hormone Use, Antibiotic Use, and Gene Modified
Organisms are directly applicable to agricultural systems. But it is difficult to see how these impact
categories can be applied to non-agricultural systems to achieve a fair comparison of non-food crop
products used in construction.
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4.2.6 Sustainability indicators
Sustainability indicators may provide a suitable alternative to the development of specific impact
categories for agricultural issues.
Defra has developed a suite of sustainability indicators (Defra ‘Sustainable development indicators in
your pocket 2006’ http://www.sustainable-development.gov.uk/publications/index.htm#2006 ), with
the following relating directly to agricultural systems:
22. Agricultural sector – fertiliser input, farmland bird population, and ammonia and methane
emissions.
23. Farming and environmental stewardship – land area covered by environmental schemes.
24. Land use – area covered by agriculture, woodland, water or river, urban.
The Government-Industry Forum on Non-Food Uses of Crops have also proposed sustainability criteria
for non-food crops (Defra and DTI, 2004). The environmental criteria include: land pollution; soil, and
biodiversity. Unfortunately, the report does not set out how these criteria are to be measured.
The Forestry Commission has generated a set of sustainability indicators for forestry
(http://www.forestry.gov.uk/forestry/infd-4xhdbf ). These include factors relating to:

Land use

Biodiversity

Soil condition

Carbon cycle.
4.2.7 End of Life
Bio-based construction materials have the potential to be reused and recycled into a variety of building
and non-building components. For example, sheep’s wool insulation can be reprocessed back into
insulation very straight forwardly or it can be reprocessed into fibre for use in clothing or packaging. In
addition bio-based building materials can act as a feedstock of non-fossil energy that can be utilised
through renewable energy processes such as anaerobic digestion at the end of the material’s useful
lives.
The biggest challenge to effective end of life utilisation is the low geographic distribution of non-timber
bio-based building materials which would be lessened with a greater uptake in the use of these
materials. Bio-based building materials can also provide outlets for waste streams from many other
industries generating bio-based materials including the textiles and clothing sectors.
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Sustainability of Biomaterials in Construction
4.2.8 Summary
Applying LCA to agricultural systems can provide a lot of useful information on the environmental
performance of these materials and guide the development of products that understand the
consequences associated with them and how to make the best use of their properties. Agricultural LCAs
require attention to the following issues:







5
Correct definition of the study’s functional unit.
Appropriate setting of study boundaries and choice of allocation method, which is particularly
important for carbon sequestration.
Assessment of machinery and infrastructure impacts
An understanding of what environmental impacts are occurring (particularly for the use of
pesticides and fertilisers) and whether where they are occurring contributes to environmental
impacts.
Consideration of all relevant environmental impacts including aspects such as land use, landscape,
soil quality and biodiversity.
Calculation of carbon sequestration and consequences of end-of-life for whole life carbon balance
and climate change impact.
Assessment of service life and end-of-life scenarios (re-use, recycling, disposal (incineration with or
without energy recovery, landfill)).
Conclusions
There are many factors to consider when assessing the sustainability of biomaterials any of which could
present limiting factors for the successful uptake of construction products using these materials.
The assessment of their environmental impact presents some complex issues to address – it is crucial
that they are assessed in a manner compatible with the assessment methods applied to alternative
materials that are used to perform the same function.
6 References
Brentrup, F; Küsters, J; Lammel, J, and Kuhlmann, H. 2002. Life Cycle Assessment of Land Use based
on the Hemeroby Concept. 7(6), 339-348.
Cowell, S and Clift, R. 1997. Impact assessment for LCAs involving agricultural production. Int. J. LCA
2(2), 99-103.
Cowell, S. 1998. Environmental life cycle assessment of agricultural systems: integration into decisionmaking. PhD thesis. Centre for Environmental Strategy, University of Surrey, Guildford, UK.
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Sustainability of Biomaterials in Construction
Defra and DTI. 2004. A strategy for non-food crops and uses. Creating value from renewable materials.
Gallagher, E (Chair). 2008. The Gallagher Review of the indirect effects of biofuels production.
Renewable Fuels Agency.
Mattsson, B; Cederberg, C, and Blix, L. 2000. Agricultural land use in life cycle assessment (LCA): case
studies of three vegetable oil crops. J. Cleaner Production, 8, 283-292.
Milà i Canals, L. 2003. Contributions to LCA methodology for agricultural systems. Site-dependency
and soil degradation impact assessment. University of Barcelona – PhD thesis.
Wegener Sleeswijk, A; Meeusen-van Onna, MJG; van Zeijts, H; Kleijn, R; Leneman, H; Reus, JAWA,
and Sengers, HHWJM. 1996. Application of LCA to agricultural products. 1. Core methodological issues;
2. Supplement to the ‘LCA Guide’; 3. Methodological background. Leiden, Centre of Environmental
Science Leiden University (CML), Centre of Agriculture and Environment (CML), Agricultural-Economic
Institute (LEI-DLO), ISBN 90-5191-104-1. CML Report 130.
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