4
BCD SPECIAL REPORT ON
HERITAGE RETROFIT
FIRST ANNUAL EDITION
CONSERVATION PRINCIPLES
AND HERITAGE IMPACT
METHODOLOGY
‘Significance’ is the collective term
used by heritage professionals to
encapsulate the diverse heritage values
that can be ascribed to a building. These
values may include artistic, symbolic,
historical, social, economic, scientific and
technological attributes.
Assessment is the key to articulating
heritage values, whether for statutory
designations or local recognition, and the
preparation of statements of significance
is generally a pre-requisite where
interventions are proposed. Statements of
significance aim to:
• identify the ‘character defining
elements’ of a building and its
curtilage
• describe the degrees of significance
(typically, from high to none) that
attach to setting, form and appearance,
components (such as doors and
windows) and material fabric
• facilitate accurate and transparent
assessment of the overall and detailed
impact of retrofit measures (from
none to high).
A successful retrofit procedure
additionally requires:
• detailed examination of existing needs
for repair and conservation
• assessment of the thermal
characteristics and performance of the
building envelope, for which expertise
in thermal imaging is a crucial
advance on theoretical U-values
• analysis of heating and electrical
systems
• understanding of moisture effects and
humidity
• assured competences in the requisite
disciplines.
A main objective of the 2012–16 European
research project Energy Efficiency for
EU Historic Districts’ Sustainability
(EFFESUS), was to develop a heritage
impact assessment methodology for the
selection and prioritisation of cost-
effective life cycle energy efficiency
improvements at the urban district
scale. For this, given that listed buildings
account for less than three per cent
of the total, an inclusive definition of
historic urban district was adopted. The
definition covers almost a quarter of the
building stock: ‘a significant grouping
of old buildings, built before 1945 and
representative of the period of their
construction or history, and comprising
buildings which are not necessarily
protected by heritage legislation’.
An essential premise was that
building-scale approaches are inefficient
and costly, and urban strategies which
identify representative typologies of
buildings will support the economies
of scale associated with mainstreaming
retrofit technologies, as well as achieve
the reductions in greenhouse gas
emissions anticipated in EU directives
(targets which the UK is independently
committed to achieving under the
Climate
Change Act 2008
). Adopting the principle
of holistic understanding of the suitability
of specific retrofit measures in any given
situation, heritage impact assessment
is one of six complementary modules
in the EFFESUS project. The other
modules are operational energy, indoor
environment (air quality and humidity),
fabric compatibility, embodied energy
(of retrofit measures) and economy.
A complementary component of
the EFFESUS project has been the
research and testing of fabric retrofits
incorporating new technologies. These
include high-performance insulating
lime mortars for use externally as render
and internally as plaster, silica aerogel
fibre insulation as infill to cavities behind
internal dry linings, and advanced window
systems with integrated air supply valves
and shading blinds connected to building
management systems.
Essential to the overarching
context is that heritage values are
maintained and interventions and their
consequences have minimal ecological
impact. Minimum intervention is a core
conservation principle and encapsulates
both objectives. It is also essential that
all actors are focussed on elaborating
properly considered retrofit solutions
that are long- rather than short-term and
do not respond to individual concerns
(such as simply reducing heating
bills) while provoking others (such as
moisture and health issues). Retrofit
solutions should be communicated
to building owners and occupants in
ways that express what they can do
rather than what they can’t and, most
importantly,
why
they have been chosen.
SAMPLE RETROFIT MEASURES
Retrofit measures fall into two main
categories: those that improve the thermal
and energy performance of buildings
(fabric and services) and those that
change the energy supply source from
fossil fuels to renewables, whether at the
individual building scale or at the urban
district level.
If the reduction of carbon emissions
is the sole or primary objective, then
a balanced approach that converts the
energy source to renewables can limit the
need for fabric interventions, especially
those which would impact prejudicially on
a building’s heritage significance. In this,
rapid advances are being made across the
multiple options for renewables – solar,
wind, biomass, ground, air and water
source heat exchangers, micro hydro-
electric and others. Advances are also
being made in defining methodologies
for cradle-to-grave carbon emission
audits to confirm whether or not certain
technologies really are ‘green’ as opposed
to just appearing to be so.
For fabric retrofits, the starting
point is to fully understand what are
the weakest areas and components of
buildings (which are not necessarily those
promoted in government programmes
such as cavity-wall insulation and window
replacement), and what are the most cost-
effective and sustainable ways of dealing
with them: from roofs to walls and floors,
windows and doors, and involuntary
leakage. New solutions such as those
researched for the EFFESUS project
need to be promoted in tandem with the
recovery of traditional solutions.
The weakest links in buildings are
often their roofs – frequently simple
to remedy with ecologically-friendly
insulation materials such as sheep’s
wool – and windows. From a heritage
significance as well as an ecological
perspective, however, windows can be
the most challenging to retrofit. What
merit is there in replacing a repairable
250-year-old timber window with one
which may, in whole or part, only last
Lörrach, Baden-Württemberg, south-west Germany:
biomass-fuelled urban-district heating plant.
District energy systems, whether for heating/cooling
or electricity, are more cost-effective and sustainable
and avoid impacting on the heritage significance of
individual buildings.