Heritage Retrofit

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.