Page 24 - Historic Churches 2013

24 BCD Special Report on Historic Churches 20th annual edition CATHEDRALC O M M U N I C A T I O N S
stones which had lost their weathering
capability. Their function in shedding
water and the retention of the architectural
lines provided by these important features
were considered more important than
conservation of the decayed stone.
The parapets were rebuilt with new brick
internally and maximum reuse of the original
stone facing. Each stone was numbered and
built back as close as possible to its original
location. The original stone, a local calcareous
siltstone with poor weathering qualities, is no
longer quarried. Second-hand stone was not
available in large enough quantities or sizes.
Ideally, a stone with a similar petrological
profile would have been used for replacements
but none was available. Another consideration
was the need for a resilient stone for parapet
copes and cornices. It was therefore decided to
use Forest of Dean blue and green/grey stone
which will gradually tone in with the existing.
The original ashlars have a rough hand-
dressed texture, in some cases axed. To integrate
the new machine-cut stone a palette of four
stone-dressing variations was developed by
the masons, not replicating the original but in
the same character. A furrowing technique to
match existing cornice and blocking course
stones was also developed. Masonry work
was commenced in lime putty but contractor
liquidation prevented completion before
winter, and the work had to be completed
early the following spring when weather
dictated the use of a hydraulic lime mix.
Roof timbers and ceiling support
Structural timber repairs to the perimeter
of the chancel roof mainly consisted of the
replacement of the wall-plate, introduction
of additional ashlar pieces to support
the eaves roof-plate and the installation
of stainless steel brackets to all timber
connections. In cases where the ceiling
joists were no longer supported at their ends
(the internal plaster coving had become
the structural support), hangers were
designed to suspend the joists from purlins
above. These all improved the structural
load paths down into the external wall.
Structural timber repair to the transept
roofs consisted of splicing new timbers to rotten
rafter ends, doubling up beetle-damaged ceiling
joists, reducing ceiling joist ends to enable
support without being built into the masonry,
and again the installation of stainless steel
brackets to all existing timber connections.
Where the ceiling lath had been attacked
by beetles, new support was provided by
threaded stainless steel rods suspended from
stainless steel flats spanning between the
ceiling joists. The lower ends of the rods were
attached to the ceiling with bronze gauze
washers bedded in plaster of Paris. Where
several adjacent laths were rotten, expanded
metal lath trays were also introduced, bedded
into the plaster, to provide additional support.
Cornices had generally lost support
from their timber framework and lath.
These were reinforced from inside the
hollow core using horizontal reinforcement
rods attached to expanded metal lath cages
bedded in plaster of Paris on the back of the
existing plaster. The rods were supported by
suspension cables fixed to stainless steel flats
spanning between the ceiling joists above.
Water penetration through the lead
roof had caused rot to the timber wall-
plates supporting the transept beams and
the resultant settlement caused cracking in
the lath and plaster beam casing. Original
pendentives were salvaged for reuse while
a new moulded cornice was run in situ, to
match the existing. Some pendentives could
not be salvaged but interestingly revealed a
lump of charcoal at their core, presumably
used as a lightweight filler around which
to mould the decorative embellishment.
Roof coverings and rainwater disposal
The works necessitated the removal of the
roof slates, GRP parapet gutters and transept
lead roofs to allow access. The lead roofs to
the transepts were recast and reinstalled in
bay sizes to current industry norms (they
were previously up to one metre wide).
The narrow parapet gutters around the
chancel have limited height in which to fall
and, to avoid a complete reconfiguration of
the transept oak roof structure to create more
fall, the gutter was reinstated using terne-
coated stainless steel sheet. This can be laid
in longer lengths than lead and without the
need for joints or steps, and has a far longer
life expectancy than plastic. Vents were added
to the flat roofs and at the pitched roof eaves
to improve ventilation in the roof space. These
will remove moisture-laden air, keep general
fabric moisture levels in check, and help to
control any surviving deathwatch beetle.
The rainwater outlets from the transept
roofs were widened to reduce the risk of
blockage. Overflow pipes were installed to
the transept gutters in case of blockage at the
parapet outlets or hoppers, and trace heating
was installed to prevent them becoming blocked
by ice. Repairs were carried out to the rainwater
pipes and one plastic pipe was replaced in
lead. The drainage system was renewed and
re-routed to nearby lakes, thus avoiding the
need for soak-aways in the heavy clay soil.
FREDERICK GIBSON RIBA AABC is an
accredited conservation architect at S T Walker
& Duckham, Worcester. The practice has a wide
portfolio including projects for English Heritage,
the National Trust, building preservation
trusts, local authorities and churches.
The chancel coved ceiling (west elevation) with
suspended threaded stainless steel rods and expanded
stainless steel laths set in plaster of Paris, bonded to
the rear of the existing plaster nibs
The north transept beam encasement after partial opening up. Existing plaster was
retained wherever possible.
The beam encasement with the pendentives reinstated