Environmental Impacts
Restore or Replace?
Craig Jones
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Thermographic image showing heat loss from traditionally constructed terraced houses
(Photo: Mitifo, iStock.com; all other photos: Jonathan Taylor) |
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As well as the 600,000 or so listed
buildings, it is estimated that almost
6 million dwellings in the UK were
built before 1919. There comes a time in
the life of every building when extensive
refurbishment is required, and for some
developers this raises the question of whether
it might be better to start again.
Many would
argue that refurbishment cannot bring old
buildings up to modern energy efficiency
standards, and these days demolition and
replacement is all too often the favoured
option. Conservationists, who inevitably
favour repair and refurbishment, counter
this by pointing to the energy used to make
new buildings.
But what does environmental
analysis show? Does it support refurbishment,
or replacement? When making the argument
for conserving traditionally constructed
buildings, conservationists need to be aware
of the facts and avoid suppositions. This article
explores the issues.
Traditional buildings were constructed
with materials and details that conduct heat
from the interior to the exterior. During
refurbishment it is possible to introduce
insulation into many elements, making
substantial improvements to their energy
use. However, some traditional details often
prevent energy performance levels to equal
those of modern construction. For example,
the appearance of fine brick or stone may
prevent the use of insulation on solid masonry
walls externally, while a finely plastered
interior may prevent insulation of the inside face, and the need for permeability and vapour
movement can cause problems for insulation
in any case. Ground floors and cross walls
provide thermal bridges that also need to be
addressed.
In addition to considering the energy used
to heat a building, any analysis also needs to
consider the ‘embodied carbon’ of building
materials. This is the amount of carbon
released during the production and processing
of materials. It mainly comes from the
consumption of fossil fuel energy throughout
the production supply chain. Environmental
analysis therefore considers consumption
at all stages, such as material extraction,
refining, transportation, processing, assembly
and fabrication.
While it is true that many older buildings
cannot be refurbished to the same energy
standards as modern construction, the
additional impact of new materials must be
considered. Refurbishment requires fewer
materials and therefore less embodied carbon.
But is this enough of a carbon swing to sway
the argument in favour of refurbishment?
To answer this question, embodied and
operational carbon need to be considered side
by side, which is called the whole-life carbon
footprint. Let’s start by looking at embodied
carbon. Embodied carbon is all too easily
forgotten because it is largely concealed from
view – most people are unaware of the high
environmental impact associated with the
production of the goods they consume.
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Left: Traditional details in new development rarely match the quality of historic architecture, no matter how good the materials. Right: Brynmor Terrace, Penmaenmawr, North Wales,
badly damaged by aluminium double glazing and
other home improvements. Double glazed timber
windows have since been installed in some of the
houses with the aid of grants from Conwy County
Borough Council under a townscape heritage
initiative. |
New-build houses in the UK (which
are among the smallest in Europe) release
on average around 45 tonnes CO2e (carbon
dioxide equivalent) during construction.
This is enough carbon to power a light bulb
continuously for over 450 years, or to power a
television for two hours a day for almost 1,440
years. It’s also enough carbon to drive to the
moon. The embodied carbon levels are, of
course, far higher for non-domestic buildings
and larger domestic estates.
To place these figures into further
perspective we need to compare them with
the operational carbon of houses. Operational
carbon varies widely but the average UK
household emits in the region of 3,300 kg of
CO2 to heat their home. This value includes
space and hot water heating, but not the
energy for lighting or appliances, which have
their own embodied versus operational carbon
balance. In contrast, the heating carbon of
a new-build UK house is around 2,000 kg of
CO2 per year. This means that rebuilding a
new house saves about 1,300 kg of operational
carbon every year. However, it comes at the
expense of the additional embodied carbon
emissions of the new construction.
To rebuild the house, 45,000 kg of carbon
dioxide is required. It therefore takes 34 years
before the savings in operational carbon
have matched the extra embodied carbon
that has been spent to rebuild the house.
This is particularly significant, because if you include the time it takes to build the
new house it will be around 2050 before
the carbon starts to pay back. The UK has
legally binding targets to reduce its carbon
emissions by 80 per cent by 2050, from a 1990
baseline. Rebuilding the UK housing stock
therefore doesn’t help to meet these targets.
Instead we must look to refurbishment
to help with this challenging target.
This, however, is where our generic
embodied carbon analysis must stop. Each
refurbishment is entirely different and
therefore each case needs to be assessed
individually. The embodied carbon of the
materials for a refurbishment needs to be
compared with the additional operational
carbon saving for the building under study.
Each building also has a different energy use
profile. This should be done on a case-by-case
basis. However, the analysis above still shows
that refurbishment is a promising option and
that refurbished buildingdo not necessarily
need the same level of thermal performance
to compete when considered from a whole-life
carbon perspective.
There are, of course, many products that
do not impact on the operational carbon of a
building. The refurbishment of such materials
and products typically brings with it a carbon
benefit. Retaining existing materials avoids
the need for new materials and products.
When it comes to refurbishment
and repair, some simple measures can
be taken to reduce the embodied carbon
footprint. One of the most effective is to
reuse materials, either on the same project
or elsewhere. Reuse of materials can save
up to 95 per cent of the embodied carbon
emissions of buying a new product.
Beyond this, there are savings to be
made through material selection. One rule
of thumb is ‘timber first’. Timber is a natural
material that has a wide range of uses and,
if responsibly sourced, its production has
a relatively low environmental impact.
Therefore if timber materials and products
are suitable it is usually a lower carbon option.
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A new terrace of traditionally detailed houses rises on the outskirts of Bath. The city was inscribed as a World Heritage Site in 1987 and opportunities for both
development and improvement are understandably limited. ‘Warmer Bath’, published by Bath Preservation Trust and the Centre for Sustainable Energy gives advice on
energy efficiency improvements for traditional homes in the city (see Further Information). |
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Timber from sustainably managed sources
also stores carbon, which is a carbon footprint
benefit. Timber is composed of approximately
50 per cent carbon by mass. What’s more, this carbon has been extracted from the
atmosphere through photosynthesis. The
carbon is stored in the timber and away from
the atmosphere until the end of the life of the
product. In fact, the carbon storage element
of timber means that it is storing more carbon
than was released to produce the timber
product. This often results in a large carbon
footprint benefit and partly explains why the
timber first principle works well.
Another good saving is the use of waterbased
instead of solvent-based paints. A
water-based paint has a carbon footprint
around a third lower than a solvent-based
one. Paint has a high embodied carbon
value and is typically applied in multiple
coats. Therefore using fewer coats, where
possible, is another good way of reducing
its impact. Likewise, painting less often
has a large benefit. Repainting a room or
an object too often makes a considerable
difference to its whole life carbon footprint.
Bricks and mortar are high-carbon
items but have a long lifespan. The embodied
carbon of these products therefore needs
to be retained for as long as possible to gain
maximum value from them. One way of doing
this is to use a lime-based mortar, which has
less embodied carbon than cement. At the end
of the lime mortar’s lifespan the brickwork
can also be dismantled and reused more easily
than if a cement-based mortar had been used.
This gives the bricks a second lifetime, offering
significant embodied carbon savings.
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Like many historic features, cast iron windows
have inimitable character, but they do drain heat.
Secondary glazing and insulated blinds offer the only
practical solution. |
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There are naturally some instances
where embodied carbon doesn’t need to
be considered. For example, the embodied
carbon of additional insulation almost always
pays back through operational carbon savings.
Due to their composition and methods of
production some types of insulation have
lower embodied carbon but if this comes
at the expense of a considerably poorer
thermal performance, they are unlikely to
be an attractive whole-life carbon choice.
So far refurbishment has come out well,
but is it always best? Unfortunately not.
There are cases where it is better to replace
than to repair. For example, if single glazed
windows are upgraded to double glazed units,
the embodied carbon of the new windows
will be paid back by the operational carbon
savings and the occupants will experience
enhanced thermal comfort.
For listed
buildings where single glazed windows are
common, this can be more difficult as the
replacement will affect the significance of
the building, and listed building consent will
be required. There may be occasions where
the original windows have been replaced
in the past, justifying a further change.
In
other cases it may be possible to introduce
draught-stripping with secondary glazing and
thermal blinds, as these measures can achieve
a thermal performance equivalent to that
of double-glazing. Alterations such as these
offer compromises that we need to consider.
When it comes down to a choice between
refurbishing or replacing, embodied carbon
often becomes a useful ally. Arguments that
point to the reduced thermal performance
of refurbished buildings should be balanced
by a careful consideration of the additional
embodied carbon expense of the new build.
While there are cases where rebuilding
is the best option there are many more
where refurbishment is the better choice.
Furthermore, without refurbishment the UK
would lose much of the charm and character
of its older building stock.
Historic and traditional architecture
contributes to our enjoyment of the places
we live and work, and makes a significant
contribution to the UK economy, particularly
through tourism. Reducing the carbon foot
print of the UK’s building stock is without
doubt extremely important, but it is not the
only criterion that needs to be taken into
account when considering the future of our
historic buildings.
Further Information
Inventory of Carbon & Energy Database, an
embodied carbon database for materials,
Circular Ecology, 2011
Domestic
Energy Fact File, Department of
Energy and Climate Change, 2012
W Anderson and J Robinson, Warmer Bath:
A Guide to Improving the Energy Efficiency
of Traditional Homes in the City of Bath,
Centre for Sustainable Energy and Bath
Preservation Trust, 2011
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The Building Conservation Directory, 2015
Author
CRAIG JONES PhD is the founder of
Circular Ecology,
which offers a range of consultancy and
research services including life cycle
assessment, footprinting and resource
efficiency studies. He is the author of the
University of Bath’s Inventory of Carbon &
Energy Database, an embodied energy and
carbon database for building materials.
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information
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