The Gridshell is essentially an industrial building, a no-frills solution to the problem posed by the museum, for a large tall open space where the timbers and frames of historic buildings can be laid out for conservation and repair, before being erected on the site of the museum. It is further used for training courses in conservation.
The design objectives for the project were for sustainable construction and energy efficiency; an early decision was made that daylighting should provide the principal means of illumination. Artificial light was seen as a necessary supplementary provision for extended hours usage, or in extreme winter conditions.
The primary use for the building required a large tall open space free of obstruction for the conservation work, with a smaller area for use as a museum and storing of the museum's artefacts. Whilst the former required a high level of energy efficient lighting, which was interpreted as daylighting during the day, the artefacts store would have intermittent use and might therefore be met by artificial light at all times.
The architect Edward Cullinan's sketch design illustrates the concept for the building, showing the tall 'conservation space'above ground level, well daylit from roof lighting, whilst the 'artefacts store' is placed at a lower level cut into the chalk hillside, artificially lit when in use.
The lightweight Gridshell structure designed by Buro Happold has been well documented elsewhere, but the purpose of this Case Study is to illustrate the nature and quality of the daylighting, together with its implication in terms of energy, for this is a 'green' building in which 'sustainability'and energy efficiency is all a part of the ethos of the museum itself.
Three important considerations were apparent:
1. The roof should contain a high degree of transparency.
2. The internal finishes should be light in colour to improve contrast rendering.
3. A balance was to be found between the need for a high level of daylight, and the need to control solar gain.
The daylighting consists of continuous rows of polycarbonate sheeting at high level, which on the north side is 'clear', letting in maximum daylight, and on the south side it has a 'bronze tint' to reduce possible sun glare. Looking up from inside the building the effect of this change is visible but not disturbing, and the impression at floor level is of an even light, ideal for the needs of conservation work. The consistency of the northern light, complemented by the variability of the southern light, formed the final scheme proposal, the rooflights being installed along the full length of the roof, to ensure acceptable contrast, the result being an even quality of daylighting, suitable for all seasonable conditions.
The use of polycarbonate sheeting in place of glass, whilst having an impact on reducing the cost, was primarily because of its light weight for erection purposes. There is a large area of glazing and if any form of glass had been specified its weight would have been a factor.
For work after dark a sufficient level of artificial light is available from a pattern of downlights, visible in the photographs.
The building was completed in May 2002 and so far there has been no need for artificial lighting to be used during the day, although both conservation work and course tuition have been in progress. The fact that no electricity has been used for lighting the space during the day is evidence of the building's energy efficiency, a strategy carried through for the building's heating and cooling.
By sinking the building into the slope of the hillside it reduced the environmental impact of the building on its surroundings, and whilst it is a large building, one is not conscious of this when visiting the site.
To sum up, the strategy for the building has been proved to be successful; so much so that the building won an RIBA architecture award, and was shortlisted for the Stirling Prize.
The final result is an enclosed space with a high level of daylight provision, estimated to provide a Daylight Factor (DF) of 10 per cent.
Gridshell Building, Weald and Downland Museum 193
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