Whilst the word atrium started as the central court of a Roman house, admitting light and air to the surrounding dwelling space, the word has taken on a wider meaning as described in the CIBSE LG10 daylight and window design.
'An interior light space enclosed on two or more sides by the walls of a building, and daylit from a roof of transparent or translucent material and, sometimes, from glazed ends or sides. It permits the entry of light to the other interior spaces, linked to it by glazed or unglazed openings.'
The atrium is therefore a further development of the dome or vault allowing daylight into the central areas of the great houses. The modern atrium will be covered by a glazed skylight, which, whilst slightly reducing the amount of daylight, monitors the external atmosphere keeping out the rain, whilst contributing to ventilation, and reducing the necessity for air-conditioning.
The proportions of the atrium and the reflective capacity of the enclosing wall surfaces are critical, and those atria which are wide in relation to their height, will perform better than taller, narrower spaces in ensuring that daylight reaches the lower levels. Having said this, the elongated atrium, which can act as an internal street at the low level, has proved successful in providing the impression of a daylit interior, even if due to its height the measured level of daylight at the lowest level will be much reduced.
In order to optimize the daylight at the lower levels one method is to set back the floor plans at the higher levels to maximize the direct view of the sky at the lower; but this has planning limitations and economic implications for the building owner.
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