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WOOD BASED PANELS IN MODERN METHODS OF CONSTRUCTION FOR

HOUSING: A GREENHOUSE GAS ABATEMENT ANALYSIS

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 95

WOOD BASED PANELS IN MODERN METHODS OF

CONSTRUCTION FOR HOUSING: A GREENHOUSE GAS
ABATEMENT ANALYSIS

M.J. Spear1*, A. Norton2, C.A.S. Hill3, C. Price4 and G.A. Ormondroyd1

1The BioComposites Centre, Bangor University, Deiniol Road, Bangor, LL57 2UW, UK
2Renuables, 41 High Street, Menai Bridge, LL59 5EF, UK
3JCH Industrial Ecology Ltd, Bangor, UK
4Colin Price Freelance Academic Services, Bangor, UK

ABSTRACT
The Construction Sector have developed a roadmap for reducing built environment carbon
emissions by 50% by 2025, which will contribute to national carbon emissions reduction
targets net zero by 2050. As energy efficiency of buildings has improved significantly, there
is a growing interest in the embodied carbon of the buildings themselves, in addition to the
operational carbon which has been the primary focus until this point. This paper reports a
study which was undertaken to compare the embodied carbon of timber framed and masonry
residential structures. The work indicates a significant benefit per dwelling for timber framed
systems. This was in line with previous studies using different building designs and different
functional units.

Embodied carbon is the carbon associated with the input materials and manufacture
(including processing, transport, etc.) of a product, as well as later demolition, recycling or
disposal. It is possible to determine embodied carbon for single materials or for whole
buildings. BS EN 15804 is a standard for evaluating and comparing the Environmental
Product Declarations of building materials, and guidance to the industry for applying this
data within calculations for buildings has been developed by RIBA and RICS. However,
many factors influence the ability and willingness of companies within the sector to consider
and apply these new calculations when designing new buildings.

Timber and wood based panels in structures are an especially interesting element within the
discussion of low carbon construction, due to their multiple different roles. The study
demonstrated that timber structures can reduce embodied carbon of a building, in addition to
providing a long-term storage role for biogenic carbon, i.e. the carbon sequestered in the
forest, but stored in the built environment. Using a stocks and flows approach to carbon
storage in buildings offers insight into the potential role of timber and wood based panels in
long term storage of carbon. It also offers an opportunity to compare carbon accounting
within bioenergy (short cycle) and long cycle systems. A discussion on wood industry co-
products and wood waste from demolition, and carbon accounting for their role in bioenergy
or energy from waste is timely.

This paper considers the importance of wood based panels in modern methods of
construction, such as timber frame and SIPs. It also highlights the role of wood based panels
in reducing the embodied carbon of new build dwellings.

INTRODUCTION
It is widely recognised that action is required to reduce greenhouse gas emissions and mitigate
or minimise the impact of global warming. Projections from the IPCC for future global
greenhouse gas (GHG) emissions allow simulation of future climate effects. While these may
be referred to on the basis of the average global temperature increase over pre-industrial levels,
such as the 1.5°C scenario, on closer inspection they show much larger changes in temperature
at individual locations. In addition, there are predicted significant changes to rainfall, extreme
weather events and ice cap melting. Data in Figure 1 is taken from the IPCC fifth assessment

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report (AR5) and show estimated temperature relative to 1986-2005 levels for a low GHG
emissions scenario and a high GHG emissions scenario.

Figure 1. Change in (a) surface temperature and (b) average precipitation based on multi-
model mean projections for 2081-2100 relative to 1986-2005, under the RCC2.6 (left, low
emissions) and RCP8.5 (right, high emissions) scenarios. Fuller information can be found in
the IPCC AR5 report (https://www.ipcc.ch/report/ar5/syr/)

The recent special report on the 1.5°C scenario indicates that we are likely to reach this level
by 2030 to 2050 if emissions continue to increase at the current rate. Warming greater than this
average value is being observed in many land regions, with the arctic two to three times higher.
In order to stabilise the temperature at the 1.5°C increase, a massive decrease in global GHG
emissions is required.

As a result of this pressing need to significantly reduce GHG emissions, many governments
have adopted national policies to monitor and mitigate emissions. Within the UK, HM
Government has set a series of carbon budgets, applicable to five-yearly periods (Table 1),
which act as stepping stones towards significant reduction by 2050. The target of 80% reduction
in emissions by 2050 was set in the Climate Change Act (2008). It was revised to net zero
(compared to 1990 levels) by 2050 in 2019. Net zero allows the total of active emissions
removals (e.g. due to photosynthesis by trees in afforestation) to be offset against emissions
from the rest of the economy. The removals of CO2 are expected to be important going forward,
given the difficulty in completely reducing emissions in certain sectors.

Spear et al.
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Table 1. Carbon budget periods and emissions figures for the UK.
Carbon budget Period Carbon budget Reduction below
level 1990 levels
First 2008-12 3,018 MtCO2e 25%
Second 2013-17 2,782 MtCO2e 31%
Third 2018-22 2,544 MtCO2e 37% reduction
Fourth 2023-27 1,950 MtCO2e 51% reduction
Fifth 2028-32 1,725 MtCO2e 57% reduction
2050 Net Zero 100% reduction

The Committee on Climate Change reports on progress towards the levels set in the carbon
budgets. We are currently in the third reporting period, and plans to ensure that we meet targets
for the fourth carbon budget are under consideration, as lead times for new technologies or
changes in industry or consumer behaviour can have significant lead times. Figure 2 shows the
progress in reducing emissions in the UK by sector, and indicates that progress in the past
decade has been greatest in industry and waste. A very strong change in the power sector has
occurred relatively recently with reduction in reliance on coal, or recommissioning of coal fired
plants for biomass energy, and increased use of renewables. By contrast, change in buildings
has been slower. The energy efficiency measures in buildings (e.g. cavity wall insulation) have
led to a general downward trend, but much remains to be done to reduce emissions by the
construction industry.

Figure 2. Progress reducing UK annual GHG emissions by sector. Source: CCC (2019) Net
Zero: The UK’s contribution to stopping global warming.

The Construction Sector

The emissions associated with the construction sector and the built environment have been
studied by the Green Construction Board (2013), in defining the 1990 benchmark for emissions
relating to construction and buildings in service. Their routemap for the built environment
indicated that it was technically possible to meet the 80% target by 2050. This relied upon
substantial reductions in operational carbon in dwellings, non-residential and infrastructure, but
also reductions in capital carbon associated with construction activity.

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The Industrial Strategy document, Construction 2025 (HM Government 2013) set an ambition
of 50% reduction in GHG emissions from the built environment by 2025. This is in line with
projections from the Green Construction Board’s routemap.

One of the areas requiring development identified by the 2011 Low Carbon Action Plan for
construction was carbon measurement tools for buildings and their materials. This can be split
into two aspects – the life cycle assessment of the material or component (i.e. global warming
potential of extraction, manufacture, transport, use, recovery or recycling and end of life) and
the operational carbon (i.e. the carbon associated with energy consumed during use in service).
At that time, some LCA data was available for individual products, and some data and systems
for evaluating operational carbon were in use.

During the eight years since the Green Construction Board report significant progress has been
made in the LCA area, with the definition of methodology for Environmental Product
Declarations (EPDs) under BS EN 15804, and the emergence of a great number of product
EPDs for construction materials. Many EPDs have been prepared for wood based panels, solid
wood, engineered wood (Figure 3). Variations in value of CO2e per kg of product for a given
panel type result from differences in manufacturing location (and the electricity grid mix in that
region), different glues and additives, different press factors and energy efficiency between
mills, and many other variables relating to the manufacture process and feedstocks. Care is
needed when selecting EPD data to ensure that it is representative of the product in use, and is
up to date. For example, improvements in energy efficiency, manufacturing efficiency and mix
of renewable energy within the electricity grid are likely to reduce EPD values, as industry
strives to improve environmental credentials.

1.0
FIBREBOARD

0.8
GWP (kg CO2 eq. per kg)

PARTICLEBOARD

0.6
GLULAM/LVL

SOLID WOOD

0.4
OSB

0.2

0.0

Figure 3. Summary graph showing the range of global warming potential (GWP) values
(equivalent to embodied carbon) reported in the literature for wood and wood-based building
materials (Hill and Dibdiakova, 2016)

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In addition to the widespread availability of EPD data, progress has been made towards defining
a system for building level calculations. In the UK RICS have also introduced a methodology
for calculating the embodied carbon of buildings (RICS 2017). In other countries similar
systems and concepts are being explored. In the Netherlands the use of LCA for buildings is
increasingly required. Many developments in this area are reviewed by Zizzo et al. (2017).

Other countries have considered the quantity of timber within the building as an environmental
benefit. In France for example, the Grenelle legislation introduced a minimum quantity of wood
per square metre floor area of a building. The initial requirement was 20 cubic decimetres per
square metre for dwellings, increasing to 35 cubic decimetres beyond 2011 (TTJ 2009,
Legifrance 2010). In Switzerland the Wood Resource Policy sets required quantities of wood
per dwelling, as well as seeking a greater quantity of Swiss wood is used (UNECE/FAO 2016).

In the operational carbon arena, the methodology has also been standardised to some extent. In
the UK the requirements for calculations are connected to the target emissions rate (TER) and
building emissions rate (BER) as defined in Approved Document L of the building regulations
(England and Wales, or equivalent in Scotland and Northern Ireland). These are calculated
based on a monthly quasi-steady state energy balance methodology SBEM (Simplified Building
Energy Model) based on BS EN ISO 52016-1 (thermal) and BS EN 15193 (lighting), or by
using approved dynamic simulation modelling software. The use of the Building Regulations
to drive energy efficiency in both residential and non-residential structures has led to
improvements in new build and where repairs or renovations necessitate structural work. In
addition, roof and cavity wall insulation, energy efficient boilers and other simple steps have
led to reductions in the existing building stock.

As operational carbon is reduced, the embodied carbon of construction has become more
prominent, leading to greater consideration of the materials used in construction, and the
building systems within which they are combined. A typical secondary school, built to 2006
regulations, had embodied carbon equivalent to 8.4 years of operational carbon. The same
school to 2010 performance levels (25% reduction in building emissions) had embodied carbon
equivalent to 10.5 years operational emissions. Projecting forward to a 70% reduction in
operational emissions, it was suggested by Target Zero (2010) that it would take 19.4 years to
reach the same level as the embodied carbon of the structure.

The balance of operational and capital carbon varies significantly from sector to sector, as
shown in Figure 4. Well heated or air conditioned buildings, such as new-build homes, schools
and offices tend to have greater operational carbon, while infrastructure projects, sports and
leisure, government buildings and warehouses tend to have higher capital carbon.

This study was undertaken as part of a larger project to consider the effects of using a greater
proportion of wood in construction (WIC). The first step was to calculate for individual
dwellings the materials consumption and the associated embodied carbon of these materials.
The data included information on the volumes of timber and wood based panels consumed,
alongside other construction materials. Within the study different construction systems (timber
frame and masonry) were compared for different house sizes and designs. Flats were also
considered in two additional systems – cross laminated timber (CLT) and concrete frame. A
wide variety of modern methods of construction (MMCs) exist, and several of them (e.g. open
panel timber frame, closed panel timber frame, structural insulated panels (SIPs), CLT) use a
significant volume of timber.

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Figure 4. UK operational carbon (OpCarb) and embodied carbon (or capital carbon CapCarb)
for buildings in 2012, segregated by sector. Source: Green Construction Board (2015)

Timber provides two distinct possibilities to abating greenhouse gas related climate change.
The carbon sequestration which occurs in the forest while the trees are growing leads to a pool
of carbon stored within that tree on felling or conversion into a product (such as timber, wood
based panels, etc). The duration of this storage depends on the product type, as reviewed by
Hill (2019) and others. In addition, structural timber and structural panels may provide a
reduction in embodied carbon in their use, when compared with other building systems and
other construction products. In this study both contributions were assessed on the basis of a
single house functional unit.

The timber framed and masonry house archetypes included in the CCC study permit an
interesting study on the impact of the wood based panels within the drive towards timber framed
construction systems. It is possible to use this to consider/quantify the importance of the wood
based panels industry within the wider supply chain of harvested wood, and its contribution to
carbon storage, and reduction of embodied carbon. Traditionally the feedstocks for wood based
panels have relied on small roundwood, e.g. forest thinnings and upper portions of the stem of
more mature trees, as well as the growing use of recycled timber. Competition for these
feedstocks from the biomass energy sector places new demands on this material, and some
consideration of the relative GHG abatement achieved by use in WBPs versus bioenergy
generation is timely.

METHOD
Single house model
Individual dwellings with 2, 3 and 4 bedrooms were evaluated, in both a masonry and an open
panel timber frame design. The footprint of the house was identical for the two structural types,
meaning that roof construction and services could be assumed equal for the site. All structural
elements were included for the substructure and superstructure, roofing timbers were included
for both structural systems. However elements such as window and door joinery systems were
excluded, to leave the effect of choice between uPVC, metal and timber frames outside the
scope of the study. Similarly the roof covering was excluded as a wide range of choice is
available for tiles and slates of different materials. Selection between roof covering systems of
differing GWP was out of scope.

Spear et al.
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Global warming potential (GWP) values were obtained for each material from recent EPDs, or
in a few cases derived from scientific literature to better represent an average product for the
UK. GWP is the impact category used within LCA and EPDs for the embodied carbon. While
this relates to all of the Kyoto protocol gases, it is expressed in kg of CO2e per functional unit.
In this study the embodied carbon or GWP was calculated on the basis of the extraction and
production stage (modules A1-A3 as set out in EN 15804), i.e. from cradle to factory gate.
Values of GWP are shown in Table 2.

For the products which contained wood or biomass, there is a storage of the carbon which was
sequestered in the forest. For this study the kg of stored sequestered carbon was calculated as
kg CO2e per kg of material, and was calculated based on the chemical composition of timber.
Values are shown in Table 2. This allowed an analysis of duration of storage to be undertaken
within a separate part of the project.

Table 2. Embodied carbon emissions and sequestered carbon stored by the products used in
the housing archetypes.
Material Data source Emissions intensities Sequestered CO2
(kg CO2e/kg) (kgCO2e/kg)

Sawn wood Wood for Good EPD 0.189 -1.598

CLT Stora Enso EPD 0.318 -1.555
Wood-based panels OSB Kronoply Gmbh EPD 0.128 -1.593
Plasterboard Gyproc Wallboard EPD 0.251 -0.072
Fibre insulation Knauf glass wool EPD 1.162 0
PUR insulation PUR average (Hill et al 2018) 2.900 0
Brick BRE UK brick EPD 0.158 0
AAC block BRE AAC EPD, IBU EPD 0.280 0
Cement mortar CAPEM GB 0.204 0
Reinforced concrete Ecoinvent 3 0.295 0
Fibre cement Rockwool Rockpanel EPD 1.752 0
rainscreen cladding

RESULTS
Single house model
The profile of embodied carbon associated with the building materials present in the dwellings
was calculated. Figure 4 shows the profile for a timber framed and a masonry system used in
the detached 4-bedroom house. It is clear that the total embodied carbon in the timber framed
example is lower than for the masonry structure, and the difference can be traced to a reduced
requirement of mortar, a reduced use of AAC blocks (lightweight autoclaved aerated concrete
blocks). Other elements vary, relating to differences in the quantities required in the two
systems. The increased timber and WBPs usage has a relatively minor impact on the total
embodied carbon as it is outweighed by the offset made in cementitious materials.

By exchanging the brick facing of the timber framed house with a timber cladding option, a
further reduction in embodied carbon was seen (Figure 5). An intermediate level of reduction
was seen when the brick facing was exchanged for a fibre cement rainscreen cladding system.
Both options offer simple additional steps to reduce the embodied carbon of a new build house.

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Figure 4. Comparison of materials used in a timber framed and a masonry 4-bed detached
house.

Comparison of embodied carbon for detached house with different

cladding systems
25
Embodied carbon per house (tCO2e)

20

15

10

0
Timber framed Timber framed, timber clad Timber framed, rainscreen Masonry
clad

sawn and engineered wood wood based panels plasterboard fibre insulation
PUR insulation brick AAC block mortar
concrete rainscreen

Figure 5. Embodied carbon associated with the materials used in four detached house designs.
Timber framed (with masonry cladding), timber framed with timber cladding, timber framed
with fibre-cement rainscreen cladding and brick and block masonry system.

A similar comparison process could easily be used to consider other permutations of wall
design, such as closed panel timber frame, structural insulated panels (SIPs), other insulation
materials, other brick options or different combinations of thicknesses of each layer while
retaining the desired level of thermal performance (U value).

Spear et al.
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The calculation process easily allows identification of material elements which contribute
significantly to the carbon emissions of the structure. In this example the cladding systems offer
a reduction compared to brick facing on the exterior of the house. In the lighter weight structures
it may also be possible to reduce the quantity of concrete used in foundations. Therefore
building level evaluations such as this offer a significant tool to the housebuilder or architect in
optimising designs for embodied carbon.

For the same house designs the stored sequestered carbon was calculated (Figure 6). The timber
and wood based panels are seen to offer a storage function which is significant, in this case 72%
of the embodied carbon would be offset by the carbon stored in the structural elements.
However, caution is required when comparing the values of sequestered carbon with the
embodied carbon emissions, as the storage function is time-related. Discussion about
appropriate methods for comparing or combining this data are still under way. For clarity,
throughout this paper, and the study which it is based upon, the two quantities were reported
separately as is best practice in the field.

Sequestered carbon for detached house archetypes (tCO2e)

Timber framed, rainscreen
Timber framed Timber framed, timber clad clad Masonry
0
Sequestered carbon stored per dwelling (tCO2e)

-2

-4

-6

-8

-10

-12

-14

-16

sawn and engineered wood wood based panels plasterboard fibre insulation
PUR insulation brick AAC block mortar
concrete rainscreen

Figure 6. Sequestered carbon stored in structural elements of the building.

It is notable that in the detached house example above, the WBPs used in flooring, wall panels
etc. contributed significantly to the storage of sequestered carbon within the building. There
was still a relatively large contribution from WBPs in the masonry houses. A similar effect was
seen for the other housing archetypes studied. In the semi-detached and terraced houses there
was OSB within party walls and spandrel panels within the roof space, in addition to the timber
frame wall elements and floor cassettes.

Table 3. Stored sequestered carbon within wood elements within the timber framed house
archetypes, expressed as weight CO2e per floor area, units kgCO2e/m2.
Detached Semi- Terrace of Bungalow Flats (block
detached 20 units of 12 units)
Sawn 77.95 75.47 72.86 93.44 56.59
timber
Wood based 29.37 28.26 29.11 15.6 39.51
panel
Plasterboard 1.14 1.46 1.51 0.75 1.33
Total 108.46 105.19 103.48 109.79 97.43

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Within the timber framed houses, the stored sequestered carbon per square metre was
compared. This has been attributed to sawn timber, wood based panels and the paper content
of plasterboard as shown in Table 3.

The quantity of timber, OSB and particleboard used is influenced by the floorplan of the
dwelling. However a greater influence was the number of storeys (note that bungalows stored
more CO2 in solid wood and less in WBPs than two-storey houses on a per floor area basis). In
the block of flats, which had three storeys the quantum of timber used was lower and wood
based panels higher, due to the greater proportion of wall elements in this additional storey, and
in the internal walls separating flats, which were a different composition than simple internal
partitions in the detached house.

It is clear that considering timber use on a floor area basis provides a reasonable method for
estimating the stored sequestered carbon in other similar designs. For example, between the
detached house and the semi-detached house the difference in floor area (117 m2 compared with
84.4 m2) had a very minor effect on the total stored sequestered carbon per area (108.46
kgCO2e/m2 cf. 105.19 kgCO2e/m2). Given that many residential properties in the UK are two-
storey, 105 kgCO2e/m2 might provide a useful rule of thumb for estimating the carbon storage
by timber frame. However differences may become significant if buildings are of different
height, or if future designs are constructed with differing dimensions of timber, for example
altering panel thickness to accommodate different insulation materials etc.

Projections for national WBP use in residential construction

The calculated data for materials utilised in the individual dwellings can be used to estimate
quantities used in large numbers of houses and flats, e.g. within a new build development in
one town, or aggregated to represent national activity. For example a model of 190,000
dwellings could represent approximate building activity in 2017-18 (where actual reported
housing starts were 193,390 for the UK, (National Statistics, 2019)).

Using an average split of 31% flats, and 69% houses, it is possible to approximate the materials
consumed, and the associated embodied carbon, and stored sequestered carbon. Within the
houses, an assumed proportion of 24% detached, 10.5% semi-detached, 15.5% end terraces,
17% mid-terraced houses, and 2% bungalows was used. Timber framed and masonry flats in
structures of nominally 3 storeys were used and concrete and CLT were used in taller structures
(nominally 6 storeys).

Using the reported percentage of timber framed dwellings 28% (STA, 2016), and an estimated
0.3% of flats in CLT, a profile of materials used to construct new buildings on a national scale
was generated. This used 772 kt of timber and wood products in the structural elements,
alongside 151 kt of insulation products, 4.472 Mt of brick and block, 916 kt of mortar and 5.023
Mt of reinforced concrete. Other elements such as plasterboard and fibre-cement rainscreen
cladding were also calculated. The embodied carbon associated with these materials is shown
in Figure 7.

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 105

Embodied carbon (million tonnes CO2e)

sawn and engineered wood
wood based panels
CLT
plasterboard
accoustic insulation
PUR insulation
fibre insulation
brick
block
mortar
reinforced concrete
fibre-cement cladding

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Figure 7. Embodied carbon associated with the various construction materials present in
190,000 new build dwellings.

Within the timber and wood based materials, wood based panels are an essential element. The
open panel timber frame system relies on the load distributing properties of the oriented strand
board (OSB) skin to deliver rigidity and resistance to shear forces in service. Flooring systems
also use the load bearing properties of particle board and OSB to good effect. Many other minor
components within the wall or roof may use plywood or OSB for load transfer, for example in
hipped roofs or as backing plates for electrical ducting.

As a result, the wood based panels comprised 33.9% of the total wood products used in the
superstructure. CLT, as a niche market comprised only 0.2%, however this is likely to change
rapidly as numbers of CLT projects increase, due to the large volumes of this product used per
dwelling.

In the case where the timber frame market share increases, the consumption of wood based
panels for housing remains strong (reaching 30.2% of wood use at 100% timber frame
adoption), and if masonry systems are preferred then percentage WBP consumption appears to
rise (reaching 41% at 100% masonry systems) due to the decrease in sawn timber used, but the
actual quantity of WBPs used decreases. This consumption depends on exact details of the
masonry building systems, i.e. flooring options.

On the national scale, the embodied carbon associated with the superstructure and foundations
of 190,000 new build dwellings (using the above split of house types and timber frame,
masonry, concrete and CLT) was calculated to be 3.041 Mt CO2e. This figure would be
increased if all services and fittings were included in the house model (i.e. plumbing ceramics,
metal pipework, electrical cables, ventilation ducting, glazing, internal joinery etc). These were
omitted from the study to allow the main effects of structural elements to be considered. It can
be reasonably assumed that the mixture of such components varies uniformly across all house
types, and is not specifically affiliated to the timber frame system or the other structural system
employed.

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Note that the figure here is low compared to the 45 Mt associated with construction activity as
a whole in Figure 4 (data for 2012, from Green Construction Board, 2015). This is due to the
relatively small size of the carbon emissions of residential construction, when compared to other
forms of activity, such as infrastructure and non-residential buildings. Differences in material
systems used (such as the greater reliance on concrete and steel) will lead to very different
trends being seen in these sectors. The 17% domestic construction contribution to capital carbon
in construction in 2012 was 7.65 MtCO2e. The 3 MtCO2e calculated here for life cycle stages
A1-3 compares well, with the balance being made up of the additional fixings and fit out, as
well as the life cycle stages which were not included in the current study (transport, on site
activities, demolition etc).

DISCUSSION
It is clear that wood based panels are an integral and essential part of the timber framing system.
As a result, there is a great onus on producers to maintain output of the grades of OSB and
particleboard which are required in timber framing, e.g. OSB3 and P5 which have the necessary
moisture resistance and load bearing qualities. There is also a clear case to argue for ongoing
access to the necessary small roundwood feedstock required to maintain this performance
quality, to support the housing market.

Wood availability is an ongoing concern for wood based panel mills. Reports of expansion in
the bioenergy sector have sparked concerns. Biomass energy produced 10% of UK energy in
2017, compared to 3% on 2008 (CCC 2018). The strength of the pallet and packaging sector,
and the cost of imports following Brexit (in addition to the anticipated delays at borders) may
also increase pressure on domestic timber reserves. Other factors such as the lack of data on
wood consumption by combined heat and power plants have also been raised by the industry
(Heald 2018).

There are signs that the wood based panels industry needs to be proactive in this market. For
example one UK mill recently invested in new planting to ensure access to timber supply in the
future. Nevertheless, consideration of wood availability on the longer time horizon may be more
stable. The CCC report Biomass in a low carbon economy (CCC 2018) explored the available
timber supply, and revised their prioritisation of timber. The preferred use is in long term
applications such as structures, while short term solutions (such as burning biomass for energy)
will increasingly be combined with carbon capture and storage. The report also called for forest
planting to increase, with an extra 27,000 ha per annum until 2030 advised. An important
finding was that per tonne of biomass used, timber in structures had the greatest effect in both
sequestering carbon, and displacing higher carbon materials.

Currently UK sawmills produce 3.7 million cubic metres of sawn timber p.a. from 6.5 million
green tonnes of timber (Forest Research 2019). Particleboard and OSB production is 3.1 million
cubic metres, using 1.2 million green tonnes of roundwood and a significant input of recycled
wood (1.6 million green tonnes ex sawmill and 0.9 million tonnes of recovered wood). Total
removals of softwoods are higher, 11.4 million green tonnes, and also supply the pulp and paper
industry, wood fuel, export and other uses such as round fencing.

An important point to note is that recycling of timber, either direct from wood processing
industries such as sawmills, secondary processors and wood users provides an additional
supply. For the quantities of timber used within the housing model above (508 kt of sawnwood),
the roundwood intake requirement was 2.082 million m3 of roundwood. From this volume it

Spear et al.
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was possible to cut the required 1.041 million m3 sawn wood, generating a significant quantity
of sawmill residues (bark, slabwood, chip and sawdust). It was also estimated that felling these
trees was estimated to be associated with generating 339 thousand m3 of small roundwood (from
the tops of the trees). Thus, although the reported oven dry material required for structural
elements was small, the forest generated a significant volume of co-products, suitable for
supplying the wood based panels sector and other sectors.

It is possible to use these co-products to good effect in the wood based panel industry, or to
supply onward into biomass energy, pet bedding, landscaping and other recycled wood
products. While small roundwood is the preferred intake of OSB mills, the particleboard and
MDF sectors may find reliance on recycled material supports future activities. However, even
here competition for wood residues with the wood pellet and bioenergy industry again emerges.

CONCLUSIONS
This paper has presented several essential steps in considering how wood based panels may
contribute to greenhouse gas abatement.

Timber is a low embodied carbon material, which can significantly contribute to reducing the
embodied carbon of building activity.

In the housing archetypes studied, the effect of using timber frame to displace masonry systems
was shown to reduce the embodied carbon for all designs.

The quantity of timber within the timber framed houses was greater than the quantity present
in the masonry houses, leading to a greater quantity of stored sequestered carbon in the timber
framed houses.

The use of wood based panels within timber frame structures is significant, and depending on
house type, up to 27% of the stored sequestered carbon was due to WBPs. In the timber framed
flats, 40% of stored carbon was within WBP elements.

Future availability of timber to produce the structural elements required within timber frame
housing was considered. Access to UK grown timber, especially the roundwood required for
OSB manufacture, is important to support the growth of timber frame in the housing sector, and
the GHG abatement which this achieves. This is compatible with cascading use of sawmill co-
products into other applications.

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