People in Glass Houses
Designing conservatories for Historic Houses
| (Vale Garden Houses)
How many times
do we see advertisements which urge us to 'extend our homes tastefully and
economically' by buying some brand or other of conservatory? For many home
owners it clearly is an attractive proposition and if well designed, a light,
timber and glass structure may present the most sensitive means of extending
an historic house, allowing the original form of the building to be seen
clearly. However, a poor design can look ugly and out of place and whether
a conservatory might be an appropriate addition to an historic building
needs careful consideration.
At the Royal Borough of Kensington and Chelsea, conservation officers deal
with a considerable number of applications for conservatories every year
both on listed buildings and unlisted buildings in conservation areas.
This is perhaps not surprising in a borough which includes some of the
wealthiest areas of London, but the fact that it also has some of the
highest residential densities in the UK makes any extension potentially
problematic, affecting the privacy of neighbours and the character of
their surroundings even before any historic building issues are considered.
Kensington and Chelsea is probably the only local authority in London
which has a specific policy on conservatories in its statutory planning
policy, or 'Unitary Development Plan'. This article deals with conservatories
primarily in an urban setting where the opportunities for conservatories
are most restricted, though generally the same principles will also apply
to suburban or rural areas.
The earliest known conservatories date from the 17th century. The first
in Britain is believed to have been constructed in the Oxford Botanic
Gardens, followed soon after by another example in the Chelsea Physic
Garden. In the 18th century, the orangery became a fashionable addition
to the English country house. At Kensington Palace in 1704 Queen Anne
commissioned a Baroque design, attributed to Hawksmoor for a free-standing
orangery in the grounds. However, it was not until the early 19th century
that conservatories came within the reach of private individuals. Glass
houses of all kinds became popular in the mid-19th century as improvements
in technology led to cheaper glass and cast iron and enabled larger sheets
of glass to be produced. Paxton's Crystal Palace, constructed for the
1851 Great Exhibition, provided a dramatic advertisement for glazed structures
and was a major influence on the popularity of conservatories. They reached
their zenith in the late Victorian and Edwardian era, but by the end of
the First World War they were no longer in fashion. In the last 30 years
there has been a resurgence in their popularity and hence the number of
firms producing a variety of proprietary and bespoke designs of differing
quality and cost.
The original purpose of a conservatory was, as in the current dictionary
definition, 'a greenhouse for tender plants'. In the late 19th and early
20th centuries they were also used for entertaining, but maintained their
role as a natural transition between house and garden. Gardening writer
Shirley Hibberd (1825-1890) wrote: 'A conservatory should be a garden
under glass and a place for frequent resort and agreeable assemblage at
all seasons and especially at times of festivity'. However, today
there are many uses to which conservatories may be put, such as living
or dining rooms. In other words, building a conservatory is just another
way of extending a house, and this should be borne in mind when considering
It is the original use as a form of greenhouse or garden room that should
perhaps inform our philosophy of design. Its success as an addition to
a house often depends on its proximity to the garden and its appearance
as a light-weight addition, clearly subservient to the parent building
and in an appropriate style. The Victorians were conscious of this. Mrs
Beeton in her Dictionary of Everyday Gardening (1896) advised that
the architectural style of a conservatory should be in harmony with that
of the house. There are three main factors in considering how a conservatory
might be designed: its location in relation to the house and garden, its
size and its detailing.
LANDED. Although ideally located for a first floor flat, the roof-top
conservatory is an alien feature in this otherwise typical Kensington
street scene. Without strict planning controls, the townscape of
neighbourhoods such as this would be dominated by roof-top conservatories.
When considering the introduction of a conservatory, location is obviously
a fundamental issue. The most natural location would usually be at garden
level to the rear of a property (the basement level in some cases). Victorian
and Edwardian conservatories are sometimes found at the front of a house
which is set in its own grounds, away from passing traffic, but hardly
ever in front of a town house, and a new conservatory would normally look
out of place in this location. In urban streets there may also be a problem
locating a conservatory at the side of a property as the views between
houses are almost always important to the character of the street. If
placed on a roof or on top of an existing extension a conservatory can
look completely bizarre, having lost its relationship to the garden. Where
the prevalent pattern at the rear of Georgian and Victorian terraced houses
is that of repeated light-wells and rear extensions (or 'closet wings'),
it is most common to place the conservatory in the light-well between
the extensions. Setting back the rear building line of the conservatory
from that of the adjacent extension also helps to maintain the rhythm
of original extensions and limits intrusion into the garden itself.
An important consideration is how the conservatory is linked to the parent
building. Where a building is listed, protection includes the whole of
the interior, not just the exterior, and the cellular nature of historic
buildings is a key element of their character. The local authority's conservation
officer is unlikely to allow a new conservatory to be merged with an existing
room by the demolition of a whole wall as this would entail considerable
removal of original fabric and alter the room's proportions and character.
Much less intervention is necessary if an existing opening is used. Ideally
this would be a door, but often it may be possible to drop the sill of
an existing window opening to create a doorway. If the window is to be
removed, consider reusing it elsewhere on the building rather than discarding
original or historic fabric, particularly if other extensions and alterations
are proposed at the same time. By minimising alterations in this way,
the original building may continue to be 'read' through the conservatory.
The size of the proposed conservatory is also of crucial importance. At
its most fundamental, all extensions must be clearly subordinate to the
parent building if the character of the original architecture is to remain
dominant, and should generally cover no more than half the width of the
When considering the footprint of a conservatory, the cellular structure
of the house and the sense of hierarchy between front and rear rooms can
be taken as a starting point. In most cases its floor area should be significantly
less than that of the adjoining room to maintain the progression through
the house from grand space to lesser spaces.
The plan-form should relate to that of the parent building and will often
be dictated by the conservatory's location. Usually a square or oblong
plan is adopted, but in some cases chamfering the corners may soften the
appearance of a large structure and a polygonal form may relate better
to existing features.
Two storey or double height conservatories are rarely appropriate additions
to listed buildings as their overall scale can look out of place, and
they may obscure relatively large areas of the elevation of the building.
The same may be true of over-elaborate roof structures.
A glance at manufacturers' catalogues at the quality end of the market
shows a preponderance of 'traditional designs' These are often based on
Victorian and Edwardian styles and consequently may appear very ornate
and fussy in appearance. On Georgian or early to mid-19th century houses
these styles are likely to clash with the rather plain and restrained
appearance of rear elevations. It is better to reflect existing character
by simplifying the design. More elaborate designs are best suited to buildings
of the Domestic Revival of the late 19th and early 20th centuries. Obviously
a quite different approach needs to be taken with buildings of the Modern
Movement and contemporary structural patterns and glazing might be utilised.
A potentially successful design may be let down by poor detailing. This
may show on the solid lower sections of the conservatory where brick construction
may give an unduly heavy or incongruous appearance. Timber panels are
often crudely constructed with applied mouldings to imitate traditional
panelling, and equal attention needs to be paid to the framing of the
glazing which should be lightweight and delicately detailed. Double-glazed
units with false glazing bars look false, particularly from the inside.
Similarly, the appearance of the roof structure may be compromised by
the use of wide aluminium cover-strips.
lights set in green painted joinery help to relate this conservatory
to the original 1930s architecture of the house and its garden.
(Vale Garden Houses)
The colour for the joinery of the conservatory
may be chosen to match the existing woodwork of the house. However, as
this colour is usually white, one interesting alternative is to paint
the conservatory dark green to reduce its visual impact.
In conservatory design over the years, glass has been used relatively
consistently although the type and quality has changed considerably as
manufacturing processes have become more efficient. On domestic conservatories
timber was the predominant framing material in the 19th and early 20th
century with cast iron generally confined to the strengthening brackets,
cresting and finials. This is in contrast with larger palm houses and
winter gardens which tended to be predominantly iron structures. For the
construction of traditional conservatories attached to listed houses today,
timber is still the preferred material as it combines strength with potentially
fine detailing. Aluminium and upvc as well as not being traditional materials
and with a quite different appearance to timber, require larger cross-sections
and inevitably much cruder detailing. Narrow sectioned steel (such as
w20) may be more appropriate for conservatories attached to buildings
of the modern movement and later.
There are a few examples of effectively 'frameless' conservatories which
are almost entirely constructed of glass. This uncompromisingly minimalist
and transparent approach to design may, on rare occasions be acceptable
on a house which is listed, but usually only in relatively concealed locations.
They may be justified where there is minimal alteration to the fabric
of the building and where they allow the original elevation to be seen
through the glazed structure.
Under current building regulations a conservatory may be considered as
an exempted structure if it meets the following criteria: it is a predominantly
glazed structure; it is at ground level; it has a floor area of less than
30sq metres; it is separated from the main building (that is, accessed
via a door rather than being an enlargement of an existing room). If these
criteria are not met the conservatory would be treated as any other extension
and would need to meet normal building regulation requirements for construction,
including drainage, ventilation, thermal insulation, and fire protection.
Thermal requirements in particular would be almost impossible to achieve
with a predominantly glazed structure.
Recommended Reading (Updated 2010)
- English Heritage, London Terrace Houses 1660-1860: A Guide to Alterations and Extensions - Part 2, London, 1996
- J Hix, The Glasshouse, Phaidon, London, 1974
- M Woods & AS Warren, Glass Houses: A History of Greenhouses, Orangeries and Conservatories, Rizzoli, New York, 1988
This article is reproduced from The Building Conservation Directory, 2000
DAVID MACDONALD is
a member of the Institute of Historic Building Conservation and is responsible
for conservation and design at the Royal Borough of Kensington and Chelsea.
The views expressed are his own and do not necessarily represent those
of the local authority.
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