Page 138 - The Building Conservation Directory 2013

1 3 8 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 3 T w e n t i e t h a N N i v e r s a r y e d i t i o n
3.4
Structure & Fabric : External Works
A new Foster & Pearson three-quarter span glasshouse with attached boiler house
Cast iron staging with a grating below covering the cast iron hot water heating
lean-to glasshouses. Walls built from brick or
stone reduced to a single skin to permit sills of
reasonably shallow depth to be placed on them
and be weathered on both sides.
In some structures underground boiler
rooms had to be incorporated because the
heating systems were not pumped and
relied on thermo-cycling (the natural rise
of warmer water leaving the boiler and the
fall of the cooling water in the return pipe),
with drainage/heating channels below
floor level and chimneys above. Decorative
cast iron gratings or wooden slats covered
these channels. Galvanised steel or lined
brick tanks were used to harvest rainwater.
Housing the tanks inside the glasshouse
had the advantage of maintaining the
stored water at ambient temperature.
Timber choices
Straight-grained Scandinavian red deal (a
softwood) was the most commonly used
timber because of its inherent stability
and durability and it tends to receive
paint more readily than most hardwoods.
However, the increasing availability of
Burmese teak in the mid 1880s meant
this could be used in the finest work or
where additional durability was required,
for example in the tropical conditions
found in orchid and other hot houses.
Ventilation
Ventilation arrangements progressed from the
inconvenient opening of individual ventilators,
which frequently disturbed plants, to remotely
operated mechanisms activating full length
side and roof ventilators.
Front ventilators were generally top-hung,
whereas types of roof ventilator included
top-hung arrangements, sliding sashes
running on rollers (manually operated or
remotely operated by chains) and, in the case
of Foster and Pearson’s patent design, a full
length lifting ridge ventilator which afforded
weathering when open.
Glazing
Glazing was generally carried out using 21oz
(per sq ft) glass in the roofs and 15oz glass
for vertical work (with average thicknesses of
approximately 2.8mm and 2mm respectively).
‘Wet glazing’, introduced from Holland in the
1770s, using linseed putty was the norm but
some manufacturers preferred ‘dry glazing’.
Here the glass was retained either by the
incorporation of metal clips, channels and caps,
or in some instances folded lead T-sections.
These lead strips had the advantage of being
available in very long continuous lengths. The
advantage of the dry system was that panes
could be replaced more easily. Various attempts
were made to help shed water more readily and
joint the panes satisfactorily, with experiments
ranging from simply butting the panes together
to cutting the glass into hexagons to help
throw water away rapidly both internally and
externally. The most common and attractive
practice for glazing roofs was to use beaver-
tailed panes (left) laid with minimal lap. Cut
with curved rather than straight upper and
lower edges, beaver-tailed panes encourage