Page 37 - The Building Conservation Directory 2013

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Professional services
Despite greater awareness and
understanding, however, the significance of
many CI buildings remains undervalued.
In some cases comparatively good
but isolated examples remain quietly
undiscovered, while other examples
may fail to become part of the historic
environment records due to difficulties in
making comparative value judgements.
Vulnerability
The threats to historic CI structures are not
as obvious as those facing more mainstream
buildings. Climate change legislation may lead
to the loss of CI buildings as unimaginative
owners, designers and planners fail to
appreciate how many of these buildings can
be successfully adapted to provide valuable,
efficient and comfortable spaces.
Long-term vacancy and often minimal
security leaves many historic CI buildings
vulnerable to theft, vandalism and arson. The
relatively high fire loads of CI buildings and
the often secluded locations may mean that
any arson attack would very quickly lead to
total destruction of the building.
Many former religious buildings are
located in picturesque rural locations, and
although there is normally a presumption
in favour of retaining existing buildings, the
arguments for demolition and redevelopment
can be persuasive. The same buildings are
often sold subject to a number of restrictive
covenants which can severely restrict their
market appeal and lead to further problems
associated with long term vacancy.
The single biggest threat to corrugated
iron is undoubtedly neglect. Fluctuating
economic fortune, the abandonment of
buildings, and a failure to undertake even
the most basic maintenance all precipitate
the decline and, in some cases, loss of these
vulnerable buildings.
Typical construction
Historic CI sheets were produced in a variety
of lengths, widths, weights and profiles.
Typically sheet sizes are 3-10 feet long and 18-
30 inches wide although other sizes were made
to order. Profiles tend to conform to the ridge
and furrow or wave pattern with an average
pitch of 3–5 inches. Historically, CI sheets
were produced according to the Standard
Wire Gauge (SWG) system of measurement.
Sheets used for roofing were typically 18 SWG
(1.2mm) thick and weighed around 1.2kgs per
square foot. This compares with commonly
available modern sheets which weigh around
0.7kgs per square foot.
Most corrugated iron was galvanised
but sheets were occasionally supplied as
‘black iron’ (ungalvanised). The quality of the
metal varied along with the quality of the
materials and the proficiency of the workers
employed in the galvanising process. Along
with other factors, this variation in quality has
undoubtedly had an impact on the long term
survival of corrugated iron.
Prefabricated buildings of all
shapes and sizes were constructed using
simple lightweight timber and metal
frames to support the CI cladding.
While many agricultural and industrial
buildings merely required the corrugated
iron to form a weather-tight shell,
large numbers of CI buildings were
constructed with elaborate interiors.
Most of the chapels, pavilions, mission
rooms and other small prefabricated
buildings that survive are constructed using
a framework of 100 x 50mm (4x 2 inch)
softwood timber. Floors are usually suspended
timber, with the entire building normally
sitting on a masonry plinth which was built
prior to the arrival of the building. Many of
these buildings have surprisingly comfortable,
sometimes even elaborate, interiors. Roof
structures vary enormously, from simple
scissor trusses to impressive arched-braced
collar trusses.
Common defects
Often thought of as an ephemeral material,
corrugated iron has in many cases far
exceeded its expected service life, but
condition is often a reflection of the
building’s use and the owner’s willingness to
undertake simple but regular maintenance.
Galvanising was perfected in this country
soon after CI was introduced and offered
a long-lasting and economical means of
preventing corrosion by applying a thin coat
of zinc to the metal sheets. Ultimately this
coating degrades or becomes damaged in
some way allowing the unprotected metal to
become exposed to the atmosphere, resulting
in corrosion.
Corrosion often begins where two sheets
overlap, the small gap setting up a capillary
attraction which allows the joint to hold water.
This can lead to an electrochemical reaction
that causes the zinc coating to preferentially
corrode beneath the overlapping sheets. This
type of reaction can also occur in positions
where fixings made from a different type of
metal have been used. This process is likely
to be accelerated in marine locations and
areas subject to acid rain due to the increased
conductivity of the electrolyte solution
that connects the metals and allows the
electrochemical reaction to occur.
Rapid and extensive corrosion can also
be found where CI wall cladding has been
partially buried due to changes in ground
levels or alterations to the plinth. Most
corrugated iron will have been painted at
some point during its life, if this has been done
regularly the incidence of serious corrosion is
normally far lower.
Mechanical damage
Holes can sometimes be seen in the CI
cladding where sheets have been removed
or replaced and fixing bolts placed in
different locations. This can lead to water
ingress and accelerated corrosion around
the hole. Impact damage caused by vehicles
can often be seen on industrial or military
buildings, and it is common to see sheets
peeling away from their supporting structure
where fixings have been damaged.
Supporting structures
Large CI buildings often have iron or steel
frames supporting the cladding. Metal ties,
rods and brackets are also common, and where
these components are concealed they are at
particular risk from undetected water ingress.
The majority of small prefabricated
buildings are constructed with softwood
frames and a large number of other timber
components. Simple maintenance is often
all that is required to ensure the timber
remains in good condition. Unfortunately,
neglect is common and timber decay is
often found in external joinery items such
as windows, doors, barge boards and fascia.
Unless there has been long term neglect
and water ingress, the timber frames and
floors are often in excellent condition.
Repair and conservation
Regardless of the type or age of a structure, the
principles of conservation and maintenance
are largely the same. The process must start
with a clear understanding of the structure
gained through documentary research and
physical examination and recording. The
significance of the structure needs to be
identified at an early stage in order to assess
how any repairs, alterations or changes in
use will impact on the special qualities of the
building. Typically this will involve retaining
the visual characteristics and as much of
the historic building fabric as possible.
Clearly it is important that any historic
The significance of a building is not always apparent from its appearance. Stripped of its corrugated iron
cladding, this early 20th-century structure forms part of a peat processing plant and is a rare survivor of an
industry dating back to medieval times. The structure is Grade II* listed and a scheduled ancient monument.