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T W E N T Y T H I R D E D I T I O N
T H E B U I L D I N G C O N S E R VAT I O N D I R E C T O R Y 2 0 1 6
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BUI LDING CONTRACTORS
ENVIRONMENTALPERFORMANCE
Assessing the impact of heritage projects on building environment
TOBIT CURTEIS and SARA CROFTS
A
S WELL
as improving the condition
of the historic fabric of a building
and its collections, publicly funded
conservation projects often aim to change
the way in which the building is used for
the benefit of all. Indeed, improving and
widening access and use is often a key
requirement projects supported by public
funding. However, changing the way in which
a historic building is used, even modestly,
can have a disproportionate effect on the
building environment, posing challenges for
the conservation of fabric and artefacts. It is
therefore important that the potential impact
of the proposed changes is fully understood
and that, where the changes increase risks to
the building, mitigation measures are built
into the design at an early stage.
The impact that changes in use have
on the building environment and fabric
is complex and not well understood. As a
result, there have been many cases where
the risks were not recognised until late in
the design process. This can be disruptive,
causing significant delays and additional
costs. While such problems can arise in all
types of projects, they are most prevalent in
smaller projects where a large professional
team may not be in place. In order to avoid
this disruption and to promote more effective
projects which will recognise and be designed
around potential risks, the Heritage Lottery
Fund (HLF) is developing measures that
would encourage potential grant applicants to
consider these issues more fully.
In the simplest cases, it is intended
that applicants should be encouraged to
carry out impact assessments themselves
or in conjunction with their architects
or other suitable professionals. Detailed
guidance will be also be given about the
issues involved and how they might affect
the project. For more complex cases it
is likely that specialist support would be
required and guidance will be given on how
to commission appropriate survey work.
This short article gives an overview of the
issues which generally cause difficulties
and the approaches that are likely to be
suggested in the forthcoming HLF guidance.
WHAT IS BUILDING ENVIRONMENT
AND PERFORMANCE AND WHY DOES
IT MATTER?
Historic buildings are vulnerable to
irreversible damage from factors including
water, light, heat and pollution which
can be referred to collectively as building
environment. Sometimes this damage is
from obvious sources such as water leaks,
and the results – crumbling plaster, mould
growth or timber decay – are plain to see.
In other cases, environmental damage is
less easy to anticipate and is associated
with apparently innocuous practices such
as the way in which the building is heated
or doors being left open. Although it is
often slower, this kind of damage can still
be serious and may even be irreversible.
Many of the buildings we are dealing
with are poorly suited to modern use or
are awkward to use for specific functions,
and are often thermally inefficient. Some
degree of alteration is usually unavoidable,
either to secure a new use for a redundant
building, or to ensure that a building
remains viable and that its future is secure.
However, the very measures which are used
to improve conditions can have unintended
consequences, and it is important to
understand that, in many cases, we are
trying to use the building in a way in which
it has never been used and for which it was
not designed. The history of conservation
is littered with examples where measures
intended to make a building more comfortable
for its users have resulted in costly and
expensive failures over the longer term.
That said, historic buildings, by their
very nature, have survived for many years
and, in many cases, are remarkably resilient
and adaptable and can even help achieve the
required environmental aims. Thick masonry
walls can provide excellent thermal buffering,
and their porous limewash and plaster finishes
can control moisture levels in the air without
the need for mechanical air conditioning.
Furthermore, much of this control is passive
and can be achieved at little or no cost. If
they are used well, these characteristics can
reduce the building’s carbon footprint and are
sustainable over the long term.
THE RISKS
There are many areas of risk associated with
modifying the building environment, but the
most common are linked to changes in heating
design and control, changes in visitor numbers
and use patterns, alterations to internal
structures (partitioning and enclosures) and
the introduction of catering facilities. In all
cases, the underlying risk is the destabilisation
of environmental conditions.
Fluctuating relative humidity can cause
an increase in salt activity resulting in the
deterioration of stone, plaster and other
inorganic structures, as well as dimensional
response in timber causing deformation and
cracking. Significant increases in relative
humidity, sometimes in hard to access areas
such as under and in roof spaces, can increase
risk of microbiological growth and encourage
chemical deterioration such as underside
corrosion on lead roofs.
Many of these potential causes of decay
Finchingfield Guildhall, Essex: previously on the Buildings at Risk Register, the Grade I listed medieval building
was restored with the help of HLF funding and is now home to a range of facilities including a museum,
function room, shop and the village library. (Photo: Finchingfield Guildhall Trust)