The new exhibition plant house and orchid
house at the Royal Botanic Garden, Edinburgh,
are structures of unusual shape and design. The
buildings have been erected ‘inside-out’ with
the supporting structures outside the glazing
to protect them from the corrosive conditions
normally existing in plant houses.
Designed by the Ministry of Public Building
and Works they are unique buildings which
have no internal framework and which depend
for support on an intricate external structure
of steel tubes and cable from which the glass
The design has enabled exotic plants to be
displayed in a natural setting on a scale never
before achieved in a glasshouse anywhere and
it has also minimised the risk of corrosion
common to ferrous metals in plant houses.
The new main exhibition house is a single
structure encompassing the entire plant area.
It is sub-divided into five compartments of
differing climatic environments and has an
orchid house adjacent to it.
Their spans are 60 ft and 50 ft and their lengths
420 ft and 100 ft respectively. The height to the
eaves is 15 ft and to the ridge 28 ft with 36 ft to
the large centre section.
The buildings have been erected from east
to west for maximum daylight and are
intercommunicating with access to the existing
Victorian Palm House. The single-span
structure gains height in the centre environment
by taking advantage of the existing site levels.
This permits changes of level to accommodate
larger plants and encourages the illusion of
Preliminary design studies showed that a
structural solution of this sort would produce
minimum shadow and light interference to the
plants inside and at the same time produce an
architectural result pleasing and well suited
to its position in the Royal Botanic Garden.
Initially, the structure was conceived as a
three-pinned portal of tubular steel members,
but as the scheme developed a more subtle
shape emerged which may be described as a
‘suspended portal frame’.
This structure, which had to be as light as
possible, is a mixture of basic portal frame and
a suspension-type structure in which the action
of the suspenders relieves the high bending
moments in the rafter members, thereby
allowing a considerable reduction in their
The side framework consists of diamond-shaped
lattice tetrahedra made up of light tubular
members which project upwards above the
rafters to twice the height of the eaves. The
main tubular members are 3-in diameter, while
the lacing members are solid bars ¾-in diameter.
The rafters, which are of rectangular hollow
section (RHS) 6 in. by 3 in., are prevented from
sagging by the suspenders, which ride over the
apex of each of the side frames. Interaction
between the suspenders and the framework
also provides resistance to side sway from the
50 Years Ago
New plant houses have
been built ‘inside out’
Reprinted from Volume 5 No. 1
General view from the west of the main exhibition plant house