Civil Engineering Reference
In-Depth Information
These basic principles are outlined in the following section of
this chapter.
but also operational energy in mind. A low carbon building
will consider the material's colour (emmissivity), thermal
conductivity (U-value) and thermal lag (decrement factor)
because they affect the thermal response, and thus operational
energy, of a building. For example, only 50-90 mm of mater-
ial is useful in thermal mass; more than that could be detri-
mental but without early modelling these decisions cannot be
assessed.
From using materials to reduce carbon through to respon-
sible specifications, reducing material consumption can be
achieved using waste products. To facilitate the recycling and
reuse process, if you are not already doing so, treat any con-
struction project as a kit of components that can be decon-
structed with minimal waste.
4.4.3.2
Focus 3: Material choice
Engineers are aware of the technical parameters of optimising
the use of a site and the framing solutions but they are often
not familiar with how the materials are used with the mindset
of reducing their impact on the embodied carbon of the con-
struction process.
Reducing embodied carbon from the outset involves choos-
ing a method of construction that is led by the materials'
response to the local climate, resource availability, recyclabil-
ity, toxicity and renewability. In simple terms, low embodied
carbon construction would comprise of local sources and waste
products typically represented by strawbale, rammed earth
and limecrete and hempcrete construction (which extract car-
bon from the atmosphere). Next in the spectrum of embodied
carbon we have recycled materials such as reclaimed bricks,
recycled steel, reused timber, recycled aggregates, glass and
then any product manufactured without the use of fossil fuels.
At the opposite side of the spectrum we see steel, clay-fired
bricks, concrete and petrochemical-based materials.
Often engineers wait for the architect to specify the materi-
als but we equally dictate the materials required structurally.
As custodian of sustainable material use, it is important also
to use the BRE
Green Guide to Specification
(Anderson
et al
.,
2002) where construction types are rated from A* to E on their
environmental impacts. There are also other guides available
from the Green Building Store, Eco-Merchants and NGS Green
Spec; in addition, manufacturers are producing more ecologic-
ally responsible materials for walls, roofs, windows and floors.
Responsible resourcing may start with the
Green Guide
but it should also be commonplace in our specifications, from
source through to the supply chain, and to how the kits of
components fit together on-site. For example, the embodied
carbon in concrete can be reduced through the use of ground
granulated blast furnace slag (GGBS), lime, pulverised fuel
ash (PFA), and secondary and recycled aggregates which often
result in increased compressive strength and reduction in cur-
ing time. The BS 8500 series for concrete specification (BSI,
2006a, 2006b) allows alternative concrete mixtures to be con-
sidered outside of Environmentally Controlled Construction
(EC
2
) and BS 8800. Responsible sourcing of timber is covered
by using Forest Stewardship Council (FSC) certified timber or
endorsed timber under the Programme for the Endorsement
of Forest Certification (PEFC) which ensures that the timber
used is managed sustainably and does not use endangered spe-
cies such as mahogany or other tropical rainforest hard woods.
Other materials such as steel, glass and masonry can be respon-
sibly managed through using products that are manufactured
by EMAS and ISO accredited companies.
Embodied carbon is not the only property that should be
considered; at any early stage it is recommended that construc-
tion schemes are optioned not only with structural efficiency
4.4.3.3
Significant sustainable wins
1. Material specification where 80% of the building complies
with
Green Guide
Rating A.
2. Consideration of the constituent materials and their
volume.
3. Responsible sourcing - BES 6001 - Framework Standard
for Responsible Resourcing of Construction Products
(BRE Global, 2009).
4. Reuse of at least 50% of the existing building façades
and reuse of 80% (by volume) of the existing building
structure.
5. Designing for robustness and easy refurbishment.
6. Understanding the insulating properties of construction
and natural materials.
4.4.3.4
Case study: WISE at Centre of Alternative Technology
The Centre of Alternative Technology (CAT) has built the 'Welsh
Institute of Sustainable Education' to showcase sustainable design
and materials that are not in mainstream construction as shown
in
Figure 4.5
. 'Treading the earth lightly' was achieved through
using lightweight materials so that strip footings could be used.
Superstructure was FSC certified timber frame with solid tim-
ber floors. The use of cement in the concrete was minimised by
replacing it with hydraulic lime or GGBS and secondary aggre-
gates. Wall construction was a combined use of rammed earth
construction with no cementitious binder, lime-hemp compos-
ite blocks and unfired earth blocks. To minimise the embodied
carbon local materials were sourced and during the construction
local labour and professional services were used.
Further information and advice can be found in the sources
listed in the references (Forde, 2009, section 10; Franklin &
Andrews, 2010/11, 2011; Harris
et al
., 2009; Structural
Engineer Briefing Note (16 March 2010)).
4.5 Construction
4.5.1 Design factors
This section describes decisions that will have to be made in
order to ensure sustainable construction. Since the choices of
