Berthold Lubetkin’s celebrated
Penguin Pool in London (1934)
Image: A penguin pauses
midway down the ramp
of Lubetkin’s pool (1934)
Aviary, London zoological garden
From The Architectural Review.
(№ 138: Sept. 1965). Pg. 186.
Collapsed goal-posts among the trees — this, undoubtedly, is the first impression of the North Aviary from Primrose Hill, and equally undoubtedly it is a very belated contribution to the Arcadian tradition in British architecture. But, within that tradition, it does not belong to the gimcrack wing that gave us so many fake ruins and other collapsed objects among trees; rather, it belongs to the tough-minded stream whose triumphs are the palm stove at Kew Gardens, or Paxton’s Victoria Regia house at Chatsworth.
In common with these great temples of acquisitive botany, the aviary is a walk-through exhibition-environment. This is not a total innovation at Regent’s Park Zoo, because one is also permitted to share the same physical space as the humming-birds, for instance. But to build on this scale and in the open is a very different problem from the creation of the small, totally artificial environment in which the humming-birds enjoy a manufactured climate secured by double-doored light-trap entrances. In the North Aviary the problem was more that of taming a piece of the existing topography and covering it with an enclosure high enough and broad enough for large birds to fly convincingly — and yet keep the public close enough to avoid the “Whipsnade effect” of sheer distance and natural surroundings making the exhibits invisible. With very little ingenuity, the form and levels of the present site would probably have made for better-than-average visibility even with an enclosure that permitted observation only from the outside. The creation of an internal observation route, by means as complex as a dog-leg bridge without intermediate supports, therefore proposes a significant improvement over outside viewing — and if the design failed to deliver this, then it would fail as architecture however handsome the covering structure. But quite obviously (though not so obviously that one does not have to explain it, alas) the bridge offers a bird’s-eye-type view of the cliff-face that no rearrangement of the solid topography could afford, except by making an equally high cliff directly opposite, and cliff-nesting birds do not nest on the sides of trenches. The other views, of birds washing and wading in the cascades for instance, are supernumerary benefits by comparison, though their sum-total is a substantial additional justification for the bridge.
Some architectural idealists have complained that the bridge is too thick, especially at its springings from the cliff, and have cited the thin-slab effect of the famous spiral ramps of the penguin pool in justification. In rebuttal (because this is a very trivial objection) one must point out that both the span and the loading here are of a totally different order, and that the aesthetic neatness of Lubetkin’s ramps had to be bought at the cost of making their springings almost solid reinforcing-rod with barely enough concrete to cover. In any case, the user of the bridge does not see its supporting musculature, only a flat ribbon of footpath zig-zagging off into space and protected by handrails and balustrades of no more than domestic strength. It all looks more perilous than it really is, and has the psychological effect of putting the visitor on what might be called an even footing with the birds — up in the air, out of contact with the earth’s surface.
Now, from the point of view of critical evaluation, the most striking aspect of the aviary is that these manipulations of the landscape are not only more crucial to the proper functioning of the building than is the visible building above ground, but at the same time they have only the most marginal effect in determining the form of the “building,” i.e., the covering cage. This is not to say that there were no determining factors at all: the size of the mesh of the netting was effectively settled by the requirement of keeping the right birds in and the wrong birds out with the minimum weight of metal. There were undoubtedly site-factors that constrained the design, notably the problem of footings and where to put them. Yet, given all this, a great variety of other possible structures could have sheltered this rockwork and this bridge; nothing inherent in the program called for the devising of an experimental tensistruttura — though it is possible that the awkwardness of the site might have constrained a more conventional design to employ some unpleasantly massive structural members.
Even the present structure is too massive to please the eyes of some people, apparently — which shows, chiefly, how much our common visual approach to tensile structures still suffers from ignorance and idealism. The stresses in structural members loaded at an angle to their axes are of a quite different order to those transmitted vertically along the axes of the columns and piers of conventional rectangular architecture. The ability of astonishingly thin cables to handle these very high loadings in tension tends to give us false hopes of the possible slenderness-ratio of the compressive members that have to absorb, at sundry cock-eyed angles, the accumulated consequences of the cables’ tensile magic. Not only this, but stiffness too is a problem in long unbraced struts. In the only previous British structure even remotely comparable to the aviary — Powell and Moya’s South Bank Skylon of 1951 — the difference between the architects’ original idealized concept of feathery lattices in compression, and the brute struts that finally got built, almost unhinged the design visually.
The aviary is one of the few large tensile structures to date in which the original design has not been coarsened in this way. Greater structural sophistication, greater structural realism, and the integration of a crack-hot engineer into the design team from a very early stage, produced a design in which the proportions of the parts are hardly altered from the original model-studies — the diameter of the sheer legs has been slightly increased for the sake of stiffness; that is all.
But, if complaints of overweight structure can be dismissed as idealistic nonsense, some of the objections to under-done detailing are less easily disposed of. While the management of the ends, joints and connections of the main metallic structure seems admirable and convincing, the tailoring of the joints and attachments of the fine-structure of the mesh seems less than housewifely, even when various technical difficulties have been allowed for (it is worth remembering that these problems were not referred to in the early model studies and have, one suspects, been solved ad hoc). Again, the failure to introduce optical corrections to the heights of the balustrades produces some careless-looking corner situations where the bridge changes direction — one balustrade up, the other down. And much of the landscaping — notoriously the sculptures for nesting-boxes — lacks the authority of the structure of the bridge and cage.
No doubt this can be altered, and will have to be when more is known about the nesting preferences of the birds; but the failure to detail-out the relationship of mesh to structure in a more convincing manner will be staring us in the face for some time to come, and while it as easy enough to forgive these small failures for the sake of the success of the grand design, they may yet prove to be the difference between a great building of the twentieth century and a major building of the nineteen-sixties.