Page 66 - Between light and shade

between light and shade, TRANSPARENCy and reflection

Vast transparent roofs cover the first open
air railway stations and large exhibition halls.
Complete glass canopies enveloped enormous
closed spaces, such as that at the Crystal Palace
of 1851 in London (39 m high) or the first large
greenhouses at the Jardin des Plantes in Paris
(1836), Kew Gardens (1849) or the Royal Palace
of Laeken (1873).

The penetration of natural light into these
open air or enclosed spaces is 60 to 70% (that of
glass, when it is clean, minus the influence of
its supporting structure) and the temperature
there fluctuates freely, as in the Pantheon and
in cathedrals.

It is very difficult to maintain a stable tem-
perature there and to prevent draughts, as the
envelope is glazed and has no thermal inertia.

In cold weather, the heat that is produced
causes currents of rising air, which accelerates
when the air cools by sinking along the outside
walls.

In hot and sunny weather, despite sun shades,
vents at the top and bottom of the enclosed space
are needed to dissipate the heat produced by the
greenhouse effect, even when using reflective
glass with a low solar factor.

Large areas of glass can also cause acoustic
discomfort, whether this is because of the noise
that reverberates from them or that caused by
heavy rain.

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