Chiswick House Conservatory

This conservatory was built in 1814 as a hothouse for growing fruit, but by about 1828 it was being used to display flowering plants. The building underwent significant alterations in 1855 when it received new glazing and a modernised heating system. The glazed superstructure was replaced in 1932 to 1933 by Messenger and Company, and replaced again between 2008 and 2010. The recent replacement closely matched the 1930s glazing pattern whilst retaining the patent clear-span post-tensioned steel rafter system and the rods and gears that operate the roof ventilation system.

The conservatory is a timber-glazed lean-to structure with cast-iron supports and steel bracing. Behind it stands a brick service range covered by a slate roof.

Plan and Setting

The building comprises one long glazed conservatory range built as a lean-to, with a semi-circular projection at its centre and pavilions at each end. A central brick wall separates it from a parallel lean-to service range at the rear, which contains the original furnaces and cisterns used to heat and irrigate the hothouse.

The conservatory stands on a south-east-facing terrace, approached by stone steps and overlooking an Italian Garden. It runs from north-east to south-west.

Exterior

The conservatory presents a symmetrical glazed timber superstructure resting on a rendered brick dwarf wall with a Portland stone plinth, cill and upstand. At the centre is a semi-circular projection with a facetted glazed roof, surmounted by a glazed drum, dome and small lead cupola topped with a weathervane. The conservatory is entered at the south-east through a pair of central glazed doors. It is lit by a continuous band of nine-paned top-hung windows beneath a clerestory of small square leaded lights.

Adjoining the central semi-circular projection is a lean-to section with nine-paned windows, a clerestory of small square leaded lights, and a glazed roof. Set lower and flanking this section are two long wings, each of 28 bays, with a continuous band of three-light top-hung windows, small square clerestory lights and a glazed roof. Each wing has a projecting gabled porch at the centre of the south-east side containing glazed double doors and glazed roofs. Pavilions at each end, set lower still, were formerly pineries and have gabled porches.

The rear elevation consists of the lean-to brick service range under a slate roof. This range has a central pedimented entrance containing a glazed double doorway with transom lights. It is rendered and detailed to imitate ashlar masonry. The first five bays flanking this entrance on each side were originally open to allow access for wagons and carts. These have been infilled with weatherboarding, ribbon glazing and boarded doors, whilst three of the bays at the north-east are set back to form a covered walkway supported on modern columns. The remaining seven bays on each side of the rear range have three-light casement and fixed windows, some with further subsidiary bars, and a doorway containing a panelled door at each end. The top of the central brick wall has lead flashing, concrete coping and cast-iron classical urns positioned next to the chimneys.

Interior of the Conservatory

The glazed timber superstructure was replaced by Messenger and Company in 1932 to 1933, and again between 2008 and 2010, closely matching the 1930s glazing pattern. However, the Messenger clear-span roofing system remains in place. This consists of cast-iron mullions anchored to the masonry dwarf wall with cast-iron brackets holding the steel tension bars that allow the rafters to span across the conservatory. The Messenger system of rods and gears for opening the roof ventilators in banks also survives. Many of these features are stamped with "MESSENGER & CO LTD LOUGHBOROUGH". These features, together with the overall form, design and glazing pattern, are of high significance, although the current glass and timberwork itself is of lesser interest given its recent replacement in 2008 to 2010, with minor repairs in 2020.

The main entrance leads into the central semi-circular projection, which has a flagstone and York stone paved floor set with decorative cast-iron underfloor heating grates. Beneath the dome is a circular geometric pebble mosaic marking the position of the original basin that contained exotic plants. Ten cast-iron piers with moulded bases and capitals support the glazed drum and dome above. An arch leads through into a barrel-vaulted entrance hall at the centre of the rear range, which has a ceiling rose and an elaborate bed moulding decorated with anthemia, bead-and-reel and foliated ornament.

The centre of the conservatory is flanked by long wings with York stone paved flooring and a flower bed containing historic camellias against the back wall, which is rendered on this side. A two-tier paved platform, supported by moulded stone columns, chamfered stone piers and stone blocks, runs the length of the front wall. This would originally have been used to display pot plants. Beneath the lower platform are large heating pipes added in 1990, whilst elsewhere there is a modern lighting system and associated electrical fixtures, none of which are of special interest. The platforms continue into and around the walls of the former pinery compartment at the south-west end, which also has a York stone paved floor, trenches for heating pipework and possibly water collection, and decorative heating grates. The former pinery pavilion at the north-east has had the platforms removed, forming a single paved open space. Adjacent to the internal entrances to the pavilions are panelled historic doors with brass door furniture that lead into the rear range.

Interior of the Service Range

The rear service range is currently (2022) used for volunteer activities and storage at the south-west end but has been converted to offices at the north-east end. This range has lean-to timber roof trusses and retains three of an original six brick and stone furnaces (or stoves) that heated the fruit house. The furnaces have brick arches for openings (now bricked up) about 1.5 metres wide and were fed by coal to reach very high temperatures in order to induce a flow of hot air along the conservatory hypocausts. These ran through the partition wall, across the planting beds, and under the windows before returning to vertical flues that emerged through the chimneys. Positioned above the furnaces are large stone water storage cisterns originally used to irrigate the conservatory plants. These cisterns are 3.9 metres long, 1.9 metres wide and 0.8 metres deep. They may once have been fed from gutters collecting rainwater from the roof of the range. This service range would originally have been used for drying and storing produce from the kitchen garden as well as preparing crops for planting. A few circular wooden poles remain fixed between the roof trusses, apparently designed to store kitchen garden produce for drying and made detachable for cleaning.

At the west end of the service range is a large brick-vaulted water tank inserted in about 1855, cutting through one of the principal truss tie beams. It may originally have been used to feed the fountain in the Italian Garden. Next to this tank is a brick pit for the boiler, originally created in 1855, but now containing a modern boiler installation which is not of special interest. The service range has a brick floor, partly laid in a herringbone pattern. The western part of this range has a stone tank next to one of the cisterns, a later inserted brick fireplace with a hob grate, and some weatherboarded partitions. The eastern part of the range has a staff room with modern kitchen units and a disabled ramp, toilets with modern sanitary ware, and offices with two brick fireplaces, some inserted modern false floors (above the earlier brick flooring), false ceilings and a number of modern fixtures, fittings and services which are not of special interest.