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STEEL
CONSTRUCTION
Embodied Carbon
2
EMBODIED CARBON
Tata Steel and the British Constructional Steelwork Association (BCSA) have worked
closely together for many years to promote the effective use of structural steelwork. This
collaborative effort ensures that advances in the knowledge of the constructional use of
steel are shared with construction professionals.
Steel is the most popular framing material for multi-storey buildings in the UK and has
a long track record of delivering high quality and cost-effective structures with proven
sustainability benefits. Steel can be naturally recycled and re-used continuously, and
offers a wide range of additional advantages such as health and safety benefits, speed
of construction, quality, efficiency, innovation, offsite manufacture and service and
support.
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The sector’s go to resource website –
www.steelconstruction.info – is a free online encyclopedia for
UK construction that shares a wealth of up-to-date, reliable
information with the construction industry in one easily
accessible place.
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The steel sector is renowned for keeping specifiers abreast of
the latest advances in areas such as fire protection of structural
steelwork and achieving buildings with the highest sustainability
ratings. Recent publications have provided detailed guidance on
CE Marking, Fire Protection, Cost and Thermal Mass and what it
means for the construction sector. Guidance is provided on all
relevant technical developments as quickly as is possible.
Tata Steel Europe
The European operations of Tata Steel comprise Europe’s second largest steel producer. With the main
steelmaking operations in the UK and Netherlands, they
supply steel and related services to the construction,
automotive, packaging, lifting and excavating, energy
and power, aerospace and other demanding markets
worldwide. The combined Tata Steel group is one of the world’s largest steel producers, with an aggregate
crude steel capacity of more than 28 million tonnes and approximately 80,000 employees across four continents.
British Constructional Steelwork Association
BCSA is the national organisation for the steel
construction industry: its Member companies undertake
the design, fabrication and erection of steelwork for all
forms of construction in building and civil engineering.
Associate Members are those principal companies
involved in the direct supply to all or some Members of
components, materials or products. Corporate Members
are clients, professional offices, educational
establishments etc which support the development of
national specifications, quality, fabrication and erection
techniques, overall industry efficiency and good practice.
EMBODIED CARBON
3
Contents
Introduction4
What is Embodied Carbon?
4
Why is Embodied Carbon Significant?
5
How Should Embodied Carbon Be Calculated?
6
The Significance of End of Life Impacts
Cradle to Gate
Cradle to Cradle
Case Study – Different End of Life Scenarios for Different Materials 8
8
8
9
End of Life Dataset by PE INTERNATIONAL
10
Whole Life Embodied Carbon Data for Common Framing Materials
11
Carbon Footprint Tool for Buildings
12
Building 1 – A Typical Business Park Office Building
Building 1 - Embodied Carbon Impacts
Building 1 - Cost and Programme
15
16
17
Building 2 – A Typical City Centre Office Building
Building 2 – Embodied Carbon Impacts
Building 2 – Cost and Programme
19
20
21
One Kingdom Street, London
One Kingdom Street – Embodied Carbon Impacts
One Kingdom Street – Cost
23
24
25
MediaCityUK, Salford
MediaCityUK – Embodied Carbon Impacts
MediaCityUK – Cost
27
28
29
Summary30
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EMBODIED CARBON
Introduction
What is Embodied Carbon?
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ASSE ODIED
B
& EM BON
CAR
The term ‘embodied carbon’ refers to the lifecycle greenhouse gas emissions (expressed
as carbon dioxide equivalents – CO2e1) that occur during the manufacture and
transport of construction materials and components, as well as the construction
process itself and end of life aspects of the building.
In recent years, the embodied carbon of construction materials has become
synonymous with the term ‘carbon footprint’.
Operational carbon is the term used to describe the emissions of carbon dioxide
during the operational or in-use phase of a building, including heating, cooling,
ventilation and lighting of the building.
Together, embodied and operational carbon comprise the total emissions of a building
throughout its lifecycle.
Extraction
Manufacture
Recycling
Transport
Embodied
Carbon
Lifecycle
Demolition
Construction
1 Climate change is caused by a number of different greenhouse gases each which have a greater or lesser impact on the
climate over time. In robust embodied carbon studies, climate change characterisation factors are used to combine the global
warming potential of different greenhouse gases to derive a single metric, in this case CO2e or carbon dioxide equivalents.
So, for example, methane has 25 times the global warming potential of CO2 and so a process that emits 1kg of CO2 and 1kg
of methane emits 26kg CO2e.
EMBODIED CARBON
For construction materials, embodied carbon should include the impacts from the
whole lifecycle of the building that they contribute to. The lifecycle aspects that
should be considered are shown on page 4. Usually, construction materials do not
contribute to the operational impacts of a building (operation, maintenance and
refurbishment), though the design that includes them can have a significant effect
on the operational performance of the building.
Why is Embodied Carbon Significant?
Reduction of operational carbon emissions from buildings is the primary sustainable
construction driver in the UK. The Government has set ambitious and legally binding
targets2 to reduce national greenhouse gas emissions and, as the operation of buildings
currently accounts for nearly half of these, significant improvement in new and existing
building performance is required if these targets are to be met.
As the operational energy efficiency of buildings is improved, the relative importance
of the embodied carbon impact is increasing. As a consequence, it is receiving more
attention by designers.
The purpose of this guide is to give designers an overview of how embodied carbon
should be considered, some practical guidance on how to assess embodied carbon on
individual projects and some case studies on how structural steelwork compares with
other framing materials.
2 The Climate Change Act commits the UK to an 80% reduction in CO2 emissions by 2050 from 1990 levels. It includes an
interim target of a 34% reduction by 2020.
5
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6
EMBODIED CARBON
How Should Embodied Carbon Be Calculated?
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The most straightforward way to determine the embodied carbon impact of different
materials and products in a building is to calculate it in a similar way to a cost model but
using rates of kgCO2e/kg rather than £/kg. The key of course is in identifying the correct
rates to use.
Lifecycle assessment (LCA) should be used to determine the embodied carbon
impacts of construction products. LCA as a methodology is in
itself flexible so that it can be used in any sphere
of life. To ensure robustness, the scope
of the LCA and aspects that it considers
tion,
struc arbon
must be consistent and rigorous to enable
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For
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comparability of one product against another.
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Within construction, this is usually achieved with a
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LCA that follows all of the lifecycle stages set out in
CA
m a L he lifecycle
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BS EN 15804.
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Designers must also ensure that they are assessing
different options using consistent data. This is an
obvious statement to make but, where embodied
carbon is concerned, careful background checking of the
scope of any data needs to be carried out.
Extraction
Extraction
Manufacture
Manufacture
Transport
Recycling
Recycling
Transport
Cradle
to
Cradle
Cradle
to
Gate
Demolition
ou
all
s set (cradle
e
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1580 )
N
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BS
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to cr
Construction
Demolition
Construction
EMBODIED CARBON
Some manufacturers present data for their products based on some but not all of
the lifecycle stages to BS EN 15804. Most frequently this will be ‘cradle to gate’
data that consider only the impacts from the extraction and manufacturing
processes.
Other manufacturers will present data for their products considering all of the
lifecycle stages to BS EN 15804. This is ‘cradle to cradle’ data (sometimes also
called ‘cradle to grave’).
A brief look at the scope of cradle to gate assessment compared to the
scope of cradle to cradle shows the significant difference between them.
7
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Comparing one material or product’s cradle to gate data against another’s cradle to
cradle data will result in a flawed analysis and an incorrect conclusion. Again, an obvious
statement to make but actually a mistake that can easily be made inadvertently since the
scope of the embodied carbon number presented is not always apparent.
Designers should therefore ensure that they confirm with a manufacturer on what basis
the number has been derived (cradle to gate, cradle to cradle etc) and that LCA has
been assessed using all the lifecycle stages in BS EN 15804 if it is not explicitly stated
and apparent within the literature.
Finally, (as with cost models) a standard material comparison on a kgCO2e/kg of
material basis should be avoided as different materials are not used in the same
quantities within a building to deliver equivalent performance. As a minimum
a kgCO2e/m2 assessment should be used for different options to consider the
effects of material intensity in the ‘as built’ condition.
Environmental Product Declarations (EPD)
The construction industry has widely adopted EPD as the
means of reporting and communicating environmental
information.
They are used to provide environmental information in a
common format.
To be comparable, EPD must have been developed with the
same scope, methodology, data quality and indicators and
designers should ensure that all the relevant life cycle stages
have also been included.
As
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8
EMBODIED CARBON
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The Significance of End of Life Impacts
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Extraction
Extraction
Manufacture
Manufacture
Transport
Recycling
Recycling
Demolition
to
cradle ents
Only
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Transport
Cradle
to
Cradle
Cradle
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Gate
Construction
Strength:
• Data is widely available for most
construction products
Weaknesses:
• Covers impacts from use of a
construction material or product only
over part of its lifecycle
• Using cradle to gate data excludes what
happens at end of life and therefore
assumes that all materials are the same
• It considers recycling, reuse, landfill,
incineration and downcycling3 to
have the same impacts. This is
simply not the case
Demolition
Construction
Strengths:
• It provides an accurate assessment of
embodied carbon impacts throughout
the lifecycle of a construction material
or product
• It ensures that comparisons of lifetime
impacts of a construction material are
correct
• Using cradle to cradle data accurately
considers the end of life impacts
Weakness:
• The previous lack of data on end of
life outcomes. This issue has now been
addressed by the PE INTERNATIONAL
dataset
What happens to a building’s structural frame once it is demolished?
3 The recycling process when the resultant material is of a lower quality than the original source; for example, using crushed
concrete as hardcore. This avoids landfilling but does not substitute concrete production.
EMBODIED CARBON
www.
steelc
Case Study – Different End of Life
Scenarios for Different Materials
Article
Built in 1953, the Lackenby open hearth steel plant was a huge
building. Over 330m long, 39m high and with a width of 70m
and incorporating over 20,000 tonnes of structural steelwork, it
dominated the Tata Steel site at Teesside. Opened in 1956 by HM
Queen Elizabeth II it remained in production for over 20 years. After
that time, the huge volumes and large column-free spaces made it
ideal for conversion to a material storage facility. But by 2004, the
building had come to the end of its useful life and it was marked for
demolition.
Once demolished, the building materials were recovered from the
site. 100% of the steel was recovered from the site and 100% was
recycled. This included the rebar in the floor slab.
The concrete from the floor slab could only be downcycled and was
crushed for low-grade fill material for hardstanding areas.
The steel from the building was recycled and supplied to hundreds of
customers for a wide variety of end uses including:
1. Structural sections used in Heathrow Terminal 5
2. Structural sections used in the new stand at the Oval cricket
ground
3. Plates used in the Paddington Station redevelopment
4. Plates fabricated into large girders for the A249 bridge to the
Isle of Sheppey
5. Galvanized strip steel to make light steel framed houses
6. Strip steel supplied to the Royal Mint to make copper plated
1p and 2p coins
7. Strip steel for automotive parts
8. Plates made into bulb flats used in the construction of ships
2
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• LAC
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Lackenby Open Hearth Steel Plant
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EMBODIED CARBON
End of Life Dataset by PE INTERNATIONAL
In order to enable designers to effectively compare embodied carbon
data for commonly used framing materials on a cradle to cradle basis,
PE INTERNATIONAL has produced an end of life dataset.
Extraction
This dataset covers the demolition and recycling impacts (modules C and D
to BS EN 15804) for common construction materials.
Manufacture
Recycling
Transport
Demolition
t
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Below is an extract from PE INTERNATIONAL’s dataset. A full list of all
products can be viewed in the construction product information article
online.
Construction
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It enables designers to add end of life impacts to manufacturer’s data and
establish a robust means to compare different options for a project.
Product
BS EN 15804 Modules
C1-C4
(kgCO2e/kg)
D
(kgCO2e/kg)
Total
C1-C4 and D
(kgCO2e/kg)
0.01
-0.0207
-0.0107
Concrete blockwork
0.0103
-0.0053
0.005
C40 concrete
0.0043
-0.0053
-0.001
C50 concrete
0.0037
-0.0053
-0.0016
Lightweight C40 concrete
0.0111
-0.0053
0.0058
Hollowcore slab
0.0006
-0.0103
-0.0097
Hot rolled plate and structural sections
0.06
-0.959
-0.899
Hot formed structural hollow sections
0.06
-1.38
-1.32
Reinforcing deck
0.061
-0.426
-0.365
Steel deck
0.06
-1.45
-1.39
Brickwork
PE INTERNATIONAL is the international market leader in strategic consultancy, software solutions and
extensive services in the field of sustainability. It has developed and maintained the GaBi software for
product sustainability.
Development of this end of life dataset was overseen by Jane Anderson, co-author of BRE’s original
Environmental Profiles Methodology for life cycle assessment of construction products and lead author
of BRE’s Green Guides to Specification.
EMBODIED CARBON
11
Whole Life Embodied Carbon Data
for Common Framing Materials
In order to assist designers, robust data has been sourced for the extraction
and manufacture lifecycle stages and combined with the end of life dataset
from PE INTERNATIONAL. The result is a robust and comprehensive dataset of
embodied carbon impacts for materials commonly used as framing materials
in construction.
Below is an extract from the full dataset. Data for all the materials included
can be viewed online, along with sources for the cradle to gate (A1-A3)
data used.
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Article
onstr
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• END
O
AND F LIFE LC
CARB EMBODIE A
D
ON D
COM
MON ATA FOR
F
MATE RAMING
RIALS
As previously stated, a standard material comparison on a kgCO2e/kg
of material basis should be avoided as different materials are not used in
the same quantities within a building to deliver equivalent performance. As a minimum
a kgCO2e/m2 assessment should be used for different options to consider the effects of
material intensity in the ‘as built’ condition.
Designers using this dataset can have confidence in its transparency, robustness and
consistency, enabling comparison between different frame options to accurately and
effectively carry out on any project.
Product
Total
A1-A3
(kgCO2e/kg)
C1-C4
(kgCO2e/kg)
D
(kgCO2e/kg)
(kgCO2e/kg)
Brickwork
0.16
0.01
-0.0207
0.15
Concrete blockwork
0.09
0.0103
-0.0053
0.10
C40 concrete
0.13
0.0043
-0.0053
0.13
C50 concrete
0.17
0.0037
-0.0053
0.17
Lightweight C40 concrete
0.17
0.0111
-0.0053
0.18
Hollowcore slab
0.2
0.0006
-0.0103
0.19
Hot rolled plate and structural sections 1
1.735
0.06
-0.959
0.84
Hot formed structural hollow sections 1
2.49
0.06
-1.38
1.17
Reinforcing steel
1.27
0.061
-0.426
0.91
2.52
0.06
-1.45
1.13
Steel deck
1
BS EN 15804 Modules
1
Fabrication (bending, cutting and welding for rebar) impacts have not been included.
Crad
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As s e o C r a d l e
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Op
tion 2
Use
cradle
to cr
data
adle
given
page
on th
is
which
inc
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dle to
gate
data
12
EMBODIED CARBON
Carbon Footprint Tool for Buildings
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A simple web tool that enables designers
of multi-storey buildings to easily estimate
the embodied carbon footprint of the
superstructure has been developed and
published online.
Designers can use the tool in two ways. In
‘auto-generate’ mode, the basic building
geometry, structural grid and chosen floor
system are used to estimate structural
material quantities using algorithms
developed by the Steel Construction
Institute (SCI) for common structural steel
solutions. Alternatively, a user may use the
‘manual input’ mode to enter the actual
material quantities for the building.
To compare the impact of a steel framed
building with a concrete framed building,
quantities should be manually input into the
tool for each option.
For both auto-generated or manually input
data, appropriate carbon emission factors
are then applied to the material quantities
to estimate the overall carbon footprint
of the building. The results are presented
as a single CO2e figure for the building,
a CO2e figure per m2 of floor area, and
a bar chart illustrating the contributions to
the total made by the various elements of the
building, i.e. frame, concrete cores, floors,
roof, fire protection and void walls.
Alternatively, the carbon emissions rates
used in the tool can be viewed on the tool’s
home tab. These can simply be incorporated
into a designer’s own spreadsheet to
generate the embodied carbon impacts of
the different options being considered. This
enables the impact of different options on
the foundations to also be included in the
assessment.
STEEL
CONSTRUCTION
Embodied Carbon
Case Studies
EMBODIED CARBON
13
14
EMBODIED CARBON
EMBODIED CARBON
15
Building 1 –
A Typical Business Park Office Building
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BUIL DY DING
1
Building
A rectangular three-storey business park office
Gross internal area:3,200m2
Floor-to-ceiling height2.8m
Building 1 is an independently developed case study by Gardiner & Theobald (G&T), Peter
Brett Associates (PBA) and Mace that has been published in the Steel Insight series in
Building and in more detail in Steel Construction: Cost.
It demonstrates the cost and programme performance of comparable structural designs
for a three-storey business park office. The same models developed by G&T for each
structural option have been used to calculate their embodied carbon impacts by applying
the carbon rates from the simple design tool to the quantities for each material.
PBA established the structural grid at 7.5m x 9m, based on an optimum grid for a typical
business park office not dictated by site constraints. Four frame types were considered:
1. Steel composite beams and composite slab
2. Steel frame and precast concrete slabs
3. Reinforced concrete flat slab
4. Insitu concrete frame with post-tensioned slab
For all options the foundations were designed as unreinforced mass concrete pads. The
core construction is steelwork cross-braced framing with a medium density blockwork
infill for the steel options and concrete shear walls for the concrete options.
For both steel options, the 30 minute fire resistance is provided by intumescent coating
to beams and bracing members and boarding to columns. For the concrete options, the
internal columns are plastered and painted for aesthetic purposes.
All options include a part-open and part-enclosed roof plant area and lift motor room.
The two steel framed options have a lightweight steel deck roof, while the concrete
options continue the concrete slab construction of the lower floors.
o
16
EMBODIED CARBON
Building 1 – Embodied Carbon Impacts
Frame and floors
+106%
200
+58%
187
153
100
97
Concrete
flat slab
PT concrete
flat slab
97
Steel
composite
0
153
Steel
precast
kgCO2e/m2 GIFA
200
+92%
+108%
+73%
Substructure
The embodied carbon impacts for each option have been
considered on a cradle to cradle basis. Only the
structural aspects of each option have been assessed,
using the dataset from the SCI’s simple design tool.
For frame and floors, the embodied carbon impact
of the steel composite option is significantly lower
than all the other options at 97kgCO2e/m2, with the
post-tensioned flat slab 58% higher at 153kgCO2e/m2,
the concrete flat slab 92% higher at 187kgCO2e/m2
and the steel precast 106% higher at 200kgCO2e/m2.
erforms
Steel outp
o provide
concrete t
died
lower embo
acts,
carbon imp
and
lower cost
nstruction
shorter co
programme
60
kgCO2e/m2 GIFA
+25%
50
40
42
30
20
24
PT concrete
flat slab
Concrete
flat slab
Steel
precast
Steel
composite
0
Total structure
+49%
+48%
328
300
268
180
100
PT concrete
flat slab
Concrete
flat slab
0
Steel
precast
For the total structure, which includes frame and upper floors,
foundations and roof construction, it can be seen that the steel
composite has the lowest embodied carbon impact at 180kgCO2e/m2.
Interestingly, steel precast and post-tensioned flat slab have similar
total impacts at 268kgCO2e/m2 and 267kgCO2e/m2, respectively, with
concrete flat slab at 328kgCO2e/m2.
267
200
Steel
composite
kgCO2e/m2 GIFA
+82%
The lighter superstructure for the steel options results
in smaller foundations than those of the concrete
options. Consequently, the impacts from the substructure are different
for each option. The foundations for the steel composite option have
an embodied carbon impact of 24kgCO2e/m2. This compares with
30kgCO2e/m2 for the steel precast option, 42kgCO2e/m2 for the
post-tensioned flat slab concrete option and 50kgCO2e/m2 for the
concrete flat slab option.
It can therefore be seen that the steel composite option has significantly
lower embodied carbon impacts than any of the other options. Whilst
the steel precast and post-tensioned flat slab concrete options have
similar embodied carbon impacts, the steel precast has significantly lower
cost and a quicker construction programme.
17
EMBODIED CARBON
Building 1 – Cost and Programme
Frame and floor
£/m2 GIFA (city of London)
160
140
+7%
+7%
+7%
155
154
154
144
The impact of the construction programme for each option has been considered
in the total building costs – the steel options benefit from lower preliminaries costs
because of their shorter construction programmes.
120
100
Total building
+2%
£/m2 GIFA (city of London)
Cost
1600
1563
+6%
+5%
1659
1640
1590
1400
The steel composite beam and slab option has both the
lowest frame and upper floors cost and lowest total
building cost. This option also has the lowest substructure
costs of all frame options due to the lighter frame
weight and the lowest roof cost due to the lightweight
steel roof deck.
The steel composite beam and slab option remains
the most competitive for Building 1, with both the
lowest frame and upper floors cost, lowest total
building cost and shortest programme.
www.
steelc
onstr
uctio
Article
s of i
ntere
st:
• COS
T CO
STUD MPARISO
N
Y-C
• COS
OST
T CO
MPAR
STUD
Y-P
I
ROG SON
RAMM
E
1200
1000
Substructure
£/m2 GIFA (city of London)
70
+5%
+21%
57
1590
68
60
50
54
+16%
A review of the steel and precast concrete slab and post-tensioned flat slab
concrete options also highlights the importance of considering total building cost
when selecting the structural frame material during design. The post-tensioned
option has a marginally lower frame and floor cost than the steel and precast
option (£154/m2 compared to £155/m2), but on a total building basis, the steel
and precast slab option has a lower cost (£1,590/m2 compared to £1,640/m2).
This is due to a lower roof cost and lower preliminaries resulting from the shorter
programme.
30
20
10
0
Programme
+3%
50
Time in weeks
45
The reinforced concrete flat slab option has both the highest frame and
upper floors cost and highest overall building cost. The frame and floors cost is 7%
higher than the steel composite and the total building cost is around 6% higher.
This option has the highest substructure costs because of the heavier frame weight,
the highest roof costs and the highest preliminaries costs due to the longest
programme.
64
40
+7%
+6%
49
48
47
40
Programme
Both steel options have very similar programme periods for both the frame
and overall construction. The steel composite option, though, provides the
quickest frame and overall duration by one week, due to the speed of laying
and distributing the steel decks. The programmes for the frame and upper floor
construction are also similar for both concrete options, as the processes involved in
constructing the structure are the same.
30
Steel composite
Concrete flat slab
Steel precast
PT concrete flat slab
n.info
Of all four options, the steel composite frame provides the fastest method of frame
construction and overall programme for Building 1.
18
EMBODIED CARBON
19
EMBODIED CARBON
Building 2 –
A Typical City Centre Office Building
www.
steelc
Article
onstr
• STE
EL
uctio
s of i
ntere
n.info
st:
CONS
TR
COST UCTION:
• COS
T CO
MP
STUD ARISON
YBUILD
ING
2
Building: An eight-storey L-shaped city centre office
Gross internal area: 16,500m2
Floor-to-ceiling height: 3.0m
Building 2 is also an independently developed case study by Gardiner & Theobald, Peter
Brett Associates (PBA) and Mace that has been published in the Steel Insight series in
Building and in more detail in Steel Construction: Cost.
In addition to demonstrating the cost and programme performance of comparable
structural designs, PBA also carried out a cradle to cradle embodied carbon assessment,
which was published too.
PBA established the structural grid at 7.5m x 15m based on experience of similar city
centre schemes, and this was used for both of the following frame options:
1. Cellular composite beams and composite slab
2. Post-tensioned band beams and slab, insitu columns.
Both options use CFA piles, with three to four piles per column pile cap. The core
construction is steel cross-braced framing with a medium density blockwork infill for the
steel option and concrete shear walls for the concrete option.
Buildings of this type normally include a basement, but the options in the study are
assumed to start from ground floor as impacts from any basement would be common to
all options.
The 60 minute fire resistance is provided to the steel framed option through intumescent
coating to beams and bracing members and boarding to columns, while the internal
columns of the concrete option are plastered and painted for aesthetic reasons.
The roof plant area is a fabricated steelwork portal frame with composite metal panel
cladding and the roof decks for both options continue the floor construction of the
lower floors.
20
EMBODIED CARBON
Building 2 – Embodied Carbon Impacts
Frame and floors
+26%
160
152
kgCO2e/m2
120
120
80
PBA assessed the options as buildings in line with the cost study designs, which used
only Portland cement for the concrete mix.
40
0
Steel composite
PT concrete flat slab
Substructure
80
+22%
67
kgCO2e/m2
60
55
0
Steel composite
PT concrete flat slab
Total building
300
+23%
kgCO2e/m2
253
200
205
100
0
300
Steel composite
PT concrete flat slab
Total building
-30% replacement mix
+11%
200
184
204
100
0
Steel composite
For the frame and floors, the post-tensioned concrete flat
slab had an embodied carbon impact 26% higher than
the steel composite option. The heavier superstructure for
the concrete option also resulted in an embodied carbon
impact for the substructure that was 22% higher than
for the steel composite option.
When considering the total building, embodied
carbon impact for the steel composite option was
205kgCO2e/m2 compared to 253kgCO2e/m2 for the
concrete option, which was 23% higher.
40
20
kgCO2e/m2
PBA’s study has been carried out on a cradle to cradle basis. It considers the whole
building, although the emissions from the structural elements represent the main carbon
differences between the options.
PT concrete flat slab
However, as cement replacement is often used to
reduce sustainability impacts, the embodied carbon
impact on both options from a 30% cement
replacement with fly ash and ground granulated
blast furnace slag was also assessed. This level of
cement replacement is considered to be reasonable
without having a significantly adverse impact on
the construction programme because of increased
curing time.
With the replacement mix, the embodied carbon
reduced to 184kgCO2e/m2 for the steel option and
to 204kgCO2e/m2 for the post-tensioned flat slab
concrete option. Though the difference between the
steel and concrete options was reduced, it was still
significant with the composite steel frame having
11% less embodied carbon than the post-tensioned
concrete frame.
www.steelco
nstruction
.info
Article of
interest:
• COST
COMPARIS
ON
STUDY - E
MBODIED
CARBON
COMPARIS
ON
Steel ou
tperform
s
concret
e to pro
vide
lower em
bodied
carbon
impacts
,
lower co
st and
shorter
constru
ction
program
me
Using
a repla
cemen
mix fo
r the
t
c
o
ncrete
reduc
es
for bo the impact
th ste
el
concr
ete op and
tions
but st
eel ma
intain
a sign
s
embod ificantly low
ied ca
e
rbon im r
pact
21
EMBODIED CARBON
Building 2 – Cost and Programme
Frame and floor
+8%
£/m2 GIFA (City of London)
240
216
198
160
80
0
Steel composite
PT concrete flat slab
Cost
The cellular steel composite option has both a lower
frame and floor cost and lower total building cost
than the post-tensioned concrete band beam option.
On a total building basis, the steel option benefits
from lower substructure costs due to the lighter
frame weight and a lower roof cost due to
the cost of the steel deck compared to the
post-tensioned slab.
Substructure
+5%
60
£/m2 GIFA (City of London)
58
61
40
20
0
Steel composite
PT concrete flat slab
Total building
www.st
eelcon
Articles
struct
of inter
es
t:
• COST
COMPA
RISON
STUDY
- COS
T
• COST
COMPA
STUDY
RISON
- PROG
RAMM
E
The steel option has a lower floor-to-floor height
(4.18m compared to 4.375m) which results in
around a 5% lower external envelope cost due to the smaller area
of cladding and also has lower preliminaries costs due to its shorter
programme. This contributes to its lowest overall total building cost.
Overall, the frame and floor cost of the steel option is over 8% lower
than the concrete option and over 3% lower on a whole building basis.
The study also highlights the importance of considering total building
cost, not just structural frame cost, because the structural frame material
and configuration impacts on many other elements, including the
substructure, roof and external cladding.
£/m2 GIFA (City of London)
+3%
1959
1900
1895
1700
1500
Steel composite
PT concrete flat slab
Programme
90
+11%
Time in weeks
80
70
72
50
30
Steel composite
PT concrete flat slab
ion.info
The total building costs for the steel options are over 3% lower than
the concrete options due to the frame and upper floor costs, as well as
smaller foundations, lightweight roofs, lower storey heights reducing
cladding costs and reduced preliminaries costs. Furthermore, the
construction durations of the steel framed solutions are shorter than the
concrete framed buildings at 11% for Building 2.
Programme
While the substructure and ground slab construction have the same
programme period - 20 weeks - for each option, the steel frame has a
significantly shorter frame and floor construction (16 weeks compared to
28 weeks for the concrete option), so the internal fit-out can start earlier.
This means the cellular steel option provides a significantly shorter frame
construction and overall programme for Building 2 compared to the
post-tensioned concrete option, with a saving of 12 weeks for the frame
and eight weeks across the programme.
22
EMBODIED CARBON
EMBODIED CARBON
23
One Kingdom Street, London
www.
steelc
Article
onstr
uctio
of int
eres
• TAR
GET
BUILD ZERO
INGS
Building: A 10-storey city centre office
Gross internal area: 33,018m2
Floor-to-ceiling height: 2.8m
One Kingdom Street is a Grade A office building completed in 2008 and used as the
office in the Target Zero research project by AECOM, Sweett Group and the SCI.
This 40m high building is rectilinear with approximate dimensions of 81m x 45m. It
accommodates 24,490m² of open plan office space on 10 floors and, on the eastern
half of the building, two basement levels providing car parking and storage. The gross
internal floor area is 33,018m². A typical office floor plate provides approximately
2,500m² of highly flexible space on a 1.5m planning grid.
One Kingdom Street has three cores and is designed around two central atria on its
southern elevation, which house six scenic wall chamber lifts. The western half of the
building is partly constructed on a podium transfer structure enclosing future works
access for Crossrail.
One Kingdom Street has a steel frame, on a typical 12m x 10.5m grid, comprising
fabricated cellular steel beams supporting a lightweight concrete slab on a profiled steel
deck. The larger span is dictated by the location of beams within the Crossrail podium
deck on which they are supported.
The foundations comprise 750mm diameter bored-piled foundations with insitu concrete
pilecaps. Ground beams provide lateral restraint to the pilecaps. The piles are the same
size as those used to support the existing Crossrail podium in order to reduce potential
differential settlement arising from the use of different pile diameters.
n.info
t:
24
EMBODIED CARBON
Frame and floors
+24%
200
One Kingdom Street –
Embodied Carbon Impacts
190
The embodied carbon impacts for both options
on One Kingdom Street have been considered on a
cradle to cradle basis.
kgCO2e/m2
152
100
0
Steel composite
PT concrete
Substructure
+26%
kgCO2e/m2
80
74
60
59
40
20
0
Steel composite
PT concrete
Total structure
600
+12%
kgCO2e/m2
506
400
452
The lighter superstructure for the steel option also
results in smaller foundations compared to the
concrete option. Consequently, the impacts from
the substructure are different for each option. The
foundations for the composite steel option have
an embodied carbon impact of 59kgCO2e/m2. This
compares with 74kgCO2e/m2 for the post-tensioned
concrete option, an increase of 26%.
st:
f intere
o
le
ic
Art
O
ET ZER
• TARG DIED
EMBO
TS
RESUL
N
O
B
CAR
rforms
Steel outpe
concrete to
r
provide lowe
rbon
embodied ca
impacts and
lower cost
When considering the both options for the building as
a whole, the steel composite option has an embodied
carbon impact of 452kgCO2e/m2, which equates to
a total of 14,937tCO2e. This compares to the post-tensioned concrete option with an
embodied carbon impact of 506kgCO2e/m2, which equates to a total of 16,716tCO2e.
The total building impact for the post-tensioned option is 12% greater than the steel
composite option.
200
0
For frame and floors, the steel composite option
has an embodied carbon impact of 152kgCO2e/m2
compared with 190kgCO2e/m2 for the post-tensioned
concrete option. The impact of the concrete option is
therefore 24% greater than that of the steel option.
ion.info
struct
eelcon
www.st
Steel composite
PT concrete
EMBODIED CARBON
www.
steelc
One Kingdom Street – Cost
Frame and floors
+19%
400
377
£/m2 GIFA
300
316
The steel option comprises composite cellular steel
beams supporting a lightweight concrete slab cast
onto profiled metal decking.
Article
onstr
25
uctio
n.info
of int
ere
st:
• TAR
GET
ZE
ALTE
RNAT RO
IV
STRU
CTUR E
FORM AL
S
200
The concrete option comprises 350mm thick
post-tensioned flat slab construction.
100
0
Steel composite
PT concrete
For the frame and floor costs alone, the steel composite option is £316/m2 compared to
£377/m2 for the post-tensioned concrete alternative. The concrete option is therefore
19% more expensive.
Total building
+4%
2000
£/m2 GIFA
1800
1869
1941
1600
1400
1200
1000
Steel composite
PT concrete
When considering the total building costs, the steel composite option is £1869/m2 or
£61.7m compared to £1941/m2 or £64.1m for the post-tensioned concrete option. The
concrete alternative is therefore 4% more expensive than the steel option.
Photo courtesy of AECOM
26
EMBODIED CARBON
27
EMBODIED CARBON
MediaCityUK, Salford
www.
steelc
Article
onstr
uctio
of int
ere
Photo courtesy of The Peel Group
st:
• TAR
GET
BUILD ZERO
INGS
Building: The 17-storey mixed-use Holiday Inn tower
Gross internal area: 18,625m2
Floor-to-ceiling height: 3.0m in hotel, 4.0m in offices
Inspired by the success of other media clusters in cities such as Dubai and Singapore,
Phase 1 of MediaCityUK started in 2007 and was completed in 2011. It is the new home
for parts of the BBC relocated from London, ITV, Coronation Street and the University of
Salford.
The mixed-use Holiday Inn tower at MediaCityUK in Salford was used in the Target Zero
research project by AECOM, Sweett Group and the SCI.
The 17-storey Holiday Inn tower is attached to the main studio building at ground,
mezzanine and first floor levels. An atrium connects the office floors of the tower block
to the studio block (floors 2 to 6). Two concrete cores, one at each extremity of the
building, provide the stability of the tower as well as housing the risers and lifts. The
foundations are 750mm diameter CFA concrete piles.
The building accommodates 7,153m² of open plan office space on five floors (floors
2 to 6) and 9,265m² of hotel space on eight floors (floors 8 to 15). The ground and
mezzanine floors accommodate the hotel reception and a restaurant. Floor 7 houses
plant for the office floors and floor 16 houses plant serving the hotel. The first floor
accommodates dressing rooms and make-up areas. The gross internal floor area of the
building is 18,625m. The 67m high building is rectilinear with approximate dimensions
of 74m x 15.3m.
Project constraints meant that unusually this building was constructed in Slimdek. For
the purposes of this case study, only the more common structural options of composite
cellular steel frame construction and concrete flat slab construction are included.
n.info
28
EMBODIED CARBON
on.info
constructi
www.steel
interest:
Article of
Frame and floors
+19%
300
MediaCityUK –
Embodied Carbon Impacts
ZERO
• TARGET
D
EMBODIE
N
O
CARB
RESULTS
259
200
The embodied carbon impacts for both standard construction options on the
Holiday Inn tower at MediaCityUK have been considered on a cradle to cradle basis.
kgCO2e/m2
218
100
0
Steel composite
Concrete flat slab
Substructure
+77%
80
75
kgCO2e/m2
60
40
For frame and floors, the steel composite option has an embodied carbon impact
of 218kgCO2e/m2 compared with 259kgCO2e/m2 for the concrete flat slab option.
The impact of the concrete option is therefore 19% greater than that of the steel
option.
The lighter superstructure for the steel option also results in smaller foundations
compared to the concrete option. Consequently, the impacts from the foundations
are different for each option. The foundations and ground floor slab for the steel
composite option have an embodied carbon impact of
42kgCO2e/m2. This compares with 75kgCO2e/m2 for
the concrete flat slab option, an increase of 77%.
42
20
0
Steel composite
Concrete flat slab
Total building
When considering both options for the building as a
whole, the steel composite option has an embodied
carbon impact of 395kgCO2e/m2, which equates to
a total of 7,352tCO2e. This compares to the concrete
flat slab option with an embodied carbon impact of
467kgCO2e/m2, which equates to a total of 8,692tCO2e.
rms
Steel outperfo
concrete to
provide lower
on
embodied carb
wer
impacts and lo
cost
+18%
467
400
The total building impact for the concrete flat slab option
is 18% greater than the steel composite option.
kgCO2e/m2
395
The embodied carbon impacts for each option have also been broken down to
show the contributions from the office and hotel parts of the building. It can
be seen that the embodied carbon impacts are lower for the steel composite
construction in both instances than for the concrete flat slab construction
alternative.
200
0
Steel composite
Concrete flat slab
Total embodied carbon
Total embodied carbon (tCO2e)
6000
4981
4644
4000
3711
2000
0
2708
Office
Hotel
Steel composite
Office
Hotel
Concrete flat slab
29
EMBODIED CARBON
www.
steelc
MediaCityUK – Cost
Frame and floors
+12%
400
£/m2 GIFA
300
The steel option comprises composite cellular steel
beams supporting a lightweight concrete slab cast
onto profiled metal decking. In the hotel part of the
building, the floor beams are UKC sections to deliver
the shallower floor construction required.
355
318
200
Article
Steel composite
The concrete option comprises 260mm thick flat slab construction
for the offices and 250mm thick flat slab construction for the
hotel.
Concrete flat slab
Total building
1868
1895
1600
When considering the total building costs, the steel composite
option is £1868/m2 or £34.8m compared to £1845/m2 or £35.3m
for the post-tensioned concrete option. The concrete alternative is
therefore 1% more expensive than the steel option.
1400
1200
1000
Steel composite
Concrete flat slab
Photo courtesy of Peel Media
£/m2 GIFA
1800
For the frame, floor and foundation costs alone, the steel
composite option is £318/m2 compared to £355/m2 for the
concrete flat slab alternative. The concrete option is therefore 12%
more expensive.
+1%
2000
uctio
n.info
of int
ere
st:
• TAR
GE
ALTE T ZERO
R
STRU NATIVE
CTU
FORM RAL
S
100
0
onstr
30
EMBODIED CARBON
Summary
When considering embodied carbon,
designers should always check
n,
o
i
t
and ensure any data that they use
c
nstru ied
o
c
r
d
for any construction material or
Fo
o
lly
t emb
robus ta is usua
product is creditable and robust.
da
A
C
n
L
o
b
Within construction, this is usually
m a
car
d fro
the
achieved with a LCA that follows
derive ws all of
t
llo
e
o
s
f
s
t
e
all of the lifecycle stages set out in
tha
tag
04
cle s
BS EN 15804.
lifecy S EN 158
B
out in
Where comparisons are being
made between materials, it is important
to ensure that the data used is similar in
scope.
Extraction
Manufacture
Cradle
to
Gate
Demolition
Some manufacturers present data for
their products based on some but not all
of the lifecycle stages to BS EN 15804.
Most frequently this will be ‘cradle
to gate’ data that consider only
the impacts from extraction and
manufacture processes.
ne
ring o ct’s
a
p
m
Co
odu
or pr data
l
a
i
r
e
te
mat
to ga
le
r’s
d
a
r
c
nothe
a
t
s
adle
again
to cr n a
le
d
i
a
cr
result d an
ll
i
w
an
data
alysis
n
n
a
d
clusio
n
o
flawe
c
rect
incor
Other manufacturers will present
data for their products considering
all of the lifecycle stages to
BS EN 15804, this is ‘cradle to
cradle’ data.
Transport
Recycling
Construction
Extraction
Manufacture
Recycling
Transport
Cradle
to
Cradle
Designers must also ensure that they
Demolition
Construction
are assessing different options using
consistent data. The most common issue is
the basis of any embodied carbon number
presented as it is not always obvious whether it is cradle to gate or cradle to cradle.
to
cradle ents
Only
sm
asses odied
le
d
a
r
mb
c
the e
of
e
d
lu
acts
inc
p
m
i
a
n
carbo fecycle of l
li
r
e
e ia
all th
n mat
o
i
t
c
tru
t
cons
oduc
or pr
As end of life impacts vary significantly between different materials, cradle to cradle
assessment should always be used when considering alternative structural options.
The dataset independently produced by PE INTERNATIONAL enables designers to add
the end of life impacts to cradle to gate data to create a robust assessment. The end
of life dataset has been incorporated into a whole life embodied carbon dataset for
common framing materials that has been published.
31
EMBODIED CARBON
Stee
l
conc outperform
rete
s
lower to provide
e
carbo mbodied
n imp
acts,
lowe
short r cost an
d
er co
nstru
ct
progr
amme ion
The case studies included demonstrate that standard steel framed buildings
outperform standard concrete framed buildings on the three key metrics of
embodied carbon impacts, cost and speed of construction. These case studies
have all been produced independently by Gardiner & Theobald, Peter Brett
Associates and Mace or AECOM, Sweett Group and the SCI.
As cement replacement is often used to reduce sustainability impacts, PBA’s
study of Building 2 included the embodied carbon impact on both structural
options from using a 30% cement replacement with fly ash and ground
granulated blast furnace slag.
U
sing
With the replacement mix, the embodied carbon reduced from
a rep
lacem
mix f
2
2
2
or th
205kgCO2e/m to 184kgCO2e/m for the steel option and from 253kgCO2e/m
ent
e
r
e
c
d
o
u
n
2
c
c
e
r
to 204kgCO2e/m for the post-tensioned concrete option. Though the
s the
et
both
impac e
steel
t
difference between the steel and concrete options was reduced, it was still
fo
optio and conc r
significant with the steel composite frame having around 11% less embodied
r
n
e
s
te
but s
maint
teel
ains
carbon than the post-tensioned concrete frame.
a
lower
Results for each aspect of the case studied considered are summarised in
the table.
si
embo gnificantly
died
impac carbon
t
Programme
(weeks)
Substructure
Total
building
Frame &
floor
Total
building
Steel composite
97
24
180
144
1563
45
Steel precast
200
30
268
155
1590
47
Concrete flat slab
187
50
328
154
1659
49
Post-tensioned flat slab
153
42
267
154
1640
48
Steel composite
120
55
205
198
1895
72
Post-tensioned flat sab
152
67
253
216
1959
80
Steel composite (replacement mix)
112
37
184
–
–
72
Post-tensioned flat slab (replacement mix)
136
52
204
–
–
80
Steel composite
152
59
452
316
1869
–
Post-tensioned flat slab
190
74
506
377
1941
–
Steel composite
218
42
395
318
1868
–
Post-tensioned flat slab
259
75
467
355
1895
–
Building 2
Building 1
Frame &
floor
One
Kingdom
Street
Cost (£/m2)
Media
CityUK
Embodied carbon (kgCO2e/m2)
www.steelconstruction.info
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related information and guidance.
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Trademarks of Tata Steel
Slimdek and UKC are trademarks of Tata Steel
Produced for:
The British Constructional Steelwork Association
www.steelconstruction.org
and
Tata Steel
www.tatasteelconstruction.com
by Barrett, Byrd Associates
www.barrett-byrd.com
September 2014