Heritage Retrofit

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22 BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION
this was considered too intrusive for most
elevations. Increased ventilation can also
increase fluctuations in humidity levels
in unheated voids, by admitting warm,
moist air. A modern closed-cell insulation
system with vapour barrier on the warm
side was therefore introduced as the
most practical option. However, Historic
England (then English Heritage) objected
to the approach as it relies on the long-
term integrity of the vapour barrier. Any
defects which arise would leave timbers
in the insulation layer vulnerable to
condensation and decay. As many of the
attic timbers are completely inaccessible,
risk management relies on specialist
monitoring technology.
GROUND FLOOR
In most areas the suspended timber floor
had been replaced with concrete in the
1970s and walls had been replastered
with a waterproof plaster. Externally,
ground levels had risen and original
lime based renders had been replaced
with cement. As a result, there was
evidence of rising damp from ground and
surface water and from leaking drains,
exacerbated by damp from wall surfaces
and window sills above.
External ground levels were therefore
reduced, drainage improved, and vapour
permeability was restored to the walls and
these were insulated. However, a non-
traditional solution was adopted for the
floor, with a conventional modern slab
laid on rigid foam insulation, and isolated
from the walls by perimeter insulation.
This replaced both the existing slab and
any surviving, but decayed timber floors.
HEATING AND VENTILATION
The carbon footprint of the building
is being further reduced by the use of
renewables, with photovoltaic panels
to be installed on the south facing roof
slopes over Garret Hostel Lane, where
they are screened from street views by
adjacent college buildings, and by using
heat extracted from boreholes in the
central court with ground source heat
pumps. Underfloor heating was therefore
used throughout, including beneath the
floor boards of the upper floors, with
sound insulation below.
Absence detectors are used to reduce
the heating level if a room is unoccupied
for more than 24 hours, and window
detectors will turn down the heating if the
window is open for more than 10 minutes
during the colder months.
Chimney flues were used to provide
controlled ventilation. Two ducts were
installed, one supplying fresh air to the
students’ room, and the other extracting
waste air from the shower rooms and
loos. In the roof a heat exchanger was
incorporated into the system to extract
almost 80 per cent of the heat from the
exhaust, which is used to preheat the
incoming fresh air supply. The system
can be reversed in the summer to provide
cooled air.
LEGACY – A MODEL SCHEME?
The extent of the interventions made at
New Court is extraordinary for a Grade I
listed building. Key changes such as the
stripping of plaster from interior wall faces,
the replacement of single glazing, and the
replacement of the remaining timber floors
at ground level with insulated concrete
slabs, are all irreversible. However, the
level of alteration is the product of its
own unique circumstances, which include
cumulative alterations to the building
over many decades, the damage caused
by dry rot in the past, the simplicity of its
interiors, and the necessity for change to
meet the requirements of health, safety,
preservation and use. Perhaps above all it
was the scientific approach to the issues
which enabled the college to gain listed
building consent for the proposals, despite
objections raised by the conservation
authorities. The level of change may not, as
a result, provide a model for other colleges
to follow, but the level of investigation and
analysis certainly does.
Beneath the romantic gothic
embellishments, this is a common
structure of bricks and mortar. Lessons
learnt from monitoring its hygrothermal
performance are equally applicable to
countless solid wall buildings throughout
the UK, from the retrofit of Victorian
terraced housing to the conversion of
industrial buildings for office, residential
and other uses. While the project has
been based on the very best available
expertise, our understanding of the long-
term effects of such changes remains
incomplete. That is why the decision to
monitor New Court for the next seven
years is so important, and it also why the
legacy of this project is so valuable.
THE AUTHOR: this article was prepared
by editor Jonathan Taylor with the help
of architect Oliver Smith, 5th Studio
).
Window shutters and architraves (left) were brought forward slightly to accommodate secondary glazing, security fixings and wall insulation. Bookcases and other
fittings on either side were designed to accommodate services and (right) to hide an en suite shower. All showers were located away from exterior walls to avoid
contributing to the moisture load. (All photos: Tim Soar)