Tropical House (“Energy for Life”), Marwell Zoo

Marwell Zoo, opened in 1972 at Colden Common near Winchester, has carried the name of its parent charity, Marwell Wildlife, since 2009. The Tropical House, named “Energy for Life”, is the second phase of a £17 million investment programme spread over eight to ten years. The zoo gives its cost as £8 million, while structural engineer DDA and the trade press say £7.8 million; the Local Growth Fund of the Enterprise M3 Local Enterprise Partnership contributed £1.5 million.

The concept architect is given as Terence O'Rourke. The works then ran as a design-and-build contract under the contractor HH Drew, for whom architect Kendall Kingscott was appointed at RIBA stage 4 to take the existing designs further. The interior was designed in autumn 2017 by Nautilus Attraction Developments with Dead Walk Designs, who tested the scheme in a 3D model and in virtual reality. On 22 November 2017 the zoo reported the roof finished and the interior under way: about 400 tonnes of soil laid over two weeks and more than 450 plants delivered from the Netherlands on seven lorries. The opening press release is dated 22 March 2018, and the trade press gave 26 March as the public opening date.

The heating changed after opening. A woodchip boiler ran at the start, with a boiler burning straw-based animal manure due to supplement it. The present system, a biomass boiler fed with briquettes pressed from the zoo's own animal waste, went live in 2021, and the Tropical House was the first building connected to it.

The plan is an elongated S that follows the slope of the site and gives a high-level entry and a low-level exit. The whole covers about 1,300 m²: 1,073 m² of rainforest exhibit, 115 m² of back-of-house and 126 m² of plant area, according to DDA Engineers. A concrete spine wall separates the exhibit from its back-of-house and receives the steel arches that carry the roof.

The roof is made of 17 three-layer ETFE cushions covering just under 1,000 m². Architen Landrell designed, manufactured and installed it with its steel structure, and no two cushions are alike. A two-level pattern of fritting tunes the light: the vertical faces admit more than the horizontal sections. Architen cites the Eden Project biomes as the inspiration. The material is inert and unaffected by humidity, the multi-layer build insulates and helps retain heat, and DDA notes that ETFE is 100 per cent recyclable. Gutters collect rainwater into two 50,000-litre tanks used for watering the plants and for the aquaria.

Dead Walk Designs describes the ceiling as a large dome, and checked it in virtual reality: the height would suffice for plants expected to grow towards the roof. Heat comes from the neighbouring energy centre, where the boiler's hot water passes through a 15,000-litre thermal store and then along an underground pipe.

The official site counts about 650 plants of 65 species. Before opening, the zoo spoke of more than 45 species, including bamboo and mango, with over 25 trees and plants 4 to 7 m tall and some specimens from Florida.

The fauna is spread through the layers of the forest. A Linné's two-toed sloth lives in the canopy; birds fly free, among them Sclater's crowned pigeon, the Nicobar pigeon and Fischer's turaco. On the forest floor live Burmese mountain tortoises and lesser goliath beetles, alongside a crocodile monitor and a leaf-cutter ant colony. A cascade drops above yellow-throated frogs whose calls can be heard. The 70,000-litre aquarium holds more than 2,500 fish according to the zoo, which announced over 1,000 before opening. The 2018 press release also mentioned a Javan chevrotain and pygmy marmosets.

The theme, the flow of energy through living systems, ties the collection to an educational strand on energy generation and climate.

The hall is walked on two levels, with elevated vantage points over the plants and animals. To protect the birds, visitors are asked to use foot baths and sanitise their hands on entering. Covered and heated, it stays practicable in wet weather. It is part of the zoo's route, and the zoo is open all year except 25 and 26 December. At launch the zoo announced an interactive area on renewable energy.

The zoo covers 57 hectares at Colden Common, near Winchester. Other buildings named in the sources include the okapi house, the “Life Among the Trees” primate area and Marwell Hall, a Grade I listed building, all in line to join the zoo's heat network.