Description

The National Botanic Garden of Wales was completed in 2000 within the 230 ha park Middleton Hall, closely following the original layout of about 1800 by William Paxton. The Great Glasshouse is situated within the generous park on top of the hills above the Tywi Valley in Carmarthenshire. The building serves the exhibition of endangered plant species and is intended to raise awareness of global topics like sustainability and environmental protection. The use of solar energy, through south orientation of the glass dome, is to exemplify possible alternatives to the exploitation of fossil fuel.

The elliptic plan with dimensions of 95 m x 55 m creates a space with a domed roof where the variety of Mediterranean species and many endangered plants can be presented. The main feature of the landscape within the glasshouse is a 6 m deep gorge with a lake at its bottom, which ensures a humid microclimate.

The structure is a round steel tube construction providing maximum transparency at minimal use of material. A peripheral concrete tie connects 24 arched girders with a maximum rise of 15 m. The roof constitutes a double-bent surface, which means that only the center arch is perpendicular to the ground whereas all other girders are leaning outwards. As an independent structure, the skin consists of secondary aluminum profiles and glass panes. The dome is inclined towards the south and fades into a massive slope towards the north to protect the building from cold northern winds. Three entrances are cut into this northern slope, which also houses a public hall, a café as well as training and secondary rooms.

In order to reduce energy consumption, interior and exterior climate of the greenhouse are monitored by a computer system; this system also controls heating and opening of the 4 m x 1.50 m roof elements to maintain the desired temperature, humidity and air circulation. Based on the combustion of biomass (wood pellets), the building is heated with a non-storage calorifier and follows sustainable design principles: the amount of carbon dioxide released during combustion approximately corresponds to the amount, which trees need for their growth. There are two tanks storing rainwater drained from the roof, which is used for watering the plants.

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Originally published in: Jürgen Adam, Katharina Hausmann, Frank Jüttner, Industrial Buildings: A Design Manual, Birkhäuser, 2004.