BCD SPECIAL REPORT ON
HERITAGE RETROFIT
FIRST ANNUAL EDITION
3
Analysis of the embodied energy and
materials of historic buildings provides
important indicators:
• it prioritises a holistic evaluation of
the long-term energy investment as
well as performance in use of all older
buildings
• it broadens perception of the
value of our built heritage beyond
delimited cultural criteria to embrace
environmental resource, societal
factors and usefulness
• it highlights the potential for
mainstreaming retrofit measures
beyond a restricted heritage sector,
up-scaling traditional methods
in tandem with appropriate new
technologies
• it facilitates the development of
manifold options for balancing
energy-related objectives with those
of heritage significance, ones that are
normal and affordable rather than
specialist and expensive.
In short, understanding sustainability
requirements provides a major opportunity
for the heritage sector to expand its field
of activity and influence in concert with
the mainstream retrofit sector.
UNDERVALUED ENERGY
PERFORMANCE
An important starting point is to address
negative assumptions regarding the
energy performance of our existing
building stock, especially older buildings
constructed using traditional materials
and techniques.
The conventional criteria for
identifying and calculating thermal
performance across the built
environment rely on simplistic thermal
transmittance or U-values, ignore
factors such as thermal inertia, and
employ standardised and generally high
assumptions concerning acceptable
indoor temperature levels. The variation
in performance as well as human comfort
levels experienced between buildings
of diverse constructional types is not
taken into account, the behavioural
patterns of building occupants as
well as their tolerance of variabilities
is ignored, and the results obtained
from different energy certification
systems – all of which are modelled
theoretically – can vary significantly.
The current measurement criteria
combine to undervalue the thermal
performance of older buildings and
create an expectation that intensive
levels of intervention are required to
make them energy efficient, ones that
anticipate conflict with their heritage
significance while proving less effective
than assumed. Additionally, there is
no industry-agreed methodology for
calculating and comparing the embodied
materials and energy of diverse typologies
of buildings by age and construction or
of interventions into them, and life-
cycle parameters and analyses are either
neglected or poor.
In 2007, based on research of
energy consumption data across a broad
cross-section of its building stock, the
Ministry of Justice in England confounded
preconceptions by demonstrating that its
oldest, pre-1900 buildings use the least
energy. The research also demonstrated that
the performance of these older buildings
was not approached in new construction
until the 1990s and 2000s, decades during
which energy use was still eight per cent
higher per square metre than for the
pre-1900 buildings. As the architect Jon
Wallsgrove has written: ‘This innovative
research... has shown that the conservation
of our architectural heritage is directly
compatible with energy conservation, rather
than being diametrically opposed, as some
environmental fundamentalists believe’.
In the light of these and related
findings both at home and abroad,
priority has been attached by the historic
environment agencies and others across
the United Kingdom to the research
and promotion of benign interventions
and limiting detrimental impacts on
the historic and traditional building
stock. Notable in this regard is the
ongoing applied research by Historic
England (formerly English Heritage) and
Historic Environment Scotland (formerly
Historic Scotland), the Building Research
Establishment, Changeworks, the Society
for the Protection of Ancient Buildings
(SPAB) and the Sustainable Traditional
Buildings Alliance (STBA), and research
conducted in historic cities including
Bath, Bristol and Edinburgh.
Austwick, Lancashire: house conversion. Heritage significance subsumes appearance and material fabric. In
this case, whereas the material fabric has been retained by overlaying solar panels, the building’s appearance
has been seriously compromised. Advances are being made in the production of solar roof tiles, also shingles
and slates, which protect the overall as well as detailed appearance of historic buildings but require
substitution of the fabric. The heritage impact methodology outlined in this article facilitates informed and
transparent decision-making in situations where choices have to be made. (All photos: Dennis Rodwell)
Thermal image composition showing heat loss from Bute House, Edinburgh (Image: Kal Murray, Eco Surveys)