Cascading Roof Design for Rainwater Harvesting

AN INNOVATIVE cascading roof has been completed at a Chinese school to harvest and recycle rainwater.

The staggered roofs allow rainfall to be collected, providing clean fresh water for schoolchildren in the village of Duling, in Guangxi, a rural province in southern China.

Bordering Vietnam, Guangxi is a mountainous region with numerous rivers and waterways. It experiences high annual rainfall but also freshwater shortages, which result in a lack of clean water for drinking and sanitation.

The revolutionary cascading roof design was created by students from the University of Hong Kong (HKU) as part of a longstanding summer school initiative to alleviate poverty and disadvantage in the region.

The initiative, named Project Mingde, saw students first being tasked in 2019 with designing a nursery school and community centre as an extension to the existing school building in Duling village. The existing building was also renovated to address its leaking roofs and poor condition.

HKU students

The initiative, named Project Mingde, saw students first being tasked in 2019 with designing a nursery school and community centre as an extension to the existing school building in Duling village. The existing building was also renovated to address its leaking roofs and poor condition.

The Duling village school is also used by the community, so the new design combines three new multi-use buildings, which are arranged around a central courtyard. These house the new nursery, teacher dormitories and both indoor and open-air community spaces for the village’s 3,000 residents’ use.

Lead HKU Architect, Elisabeth Lee said: “The scarcity of water available for cleaning tasks and restroom maintenance resulted in an environment that was decidedly inadequate for the health of children. Fundamental sanitation measures, such as flushing toilets and handwashing, were absent.”

Cascading Roof Design

Providing clean water was an essential priority for the school’s design, with Project Mingde‘s students first undertaking a comprehensive analysis to find out requirements. The solution was three buildings of varying heights with roofs that channel rainfall into a lotus pond.

“Taking into consideration the site’s topography, airflow, landscape views, and culture, the building adopts a cascading form, culminating in a series of tiered roofs,” adds Elisabeth.

Rainwater flows from each roof, one to another, from which it is drained into the pond below. From there it is fed into an underground system, filtered and then pumped into the buildings for use.

“The system supplies an average of about 1,500 litres of recycled rainwater each day for practical use, dependent on average rainfall patterns,” explained Elisabeth Lee.

Sustainable Community Living

The village of Duling is mainly made up of a Chinese ethnic subgroup called Hakka, which is strongly represented in Guangxi.

Elisabeth Lee said that the design inspiration for the building’s form was derived from “fundamental Hakka principles”, in particular its emphasis on sustainable and integrated communal living.

This idea is realised as the ground floor of the centre’s three buildings is used as a nursery in the mornings, before transforming into a community space in the afternoon and evening, illustrating the “fluidity of community life” in the Hakka village.

Likewise, the second storey of the school houses teachers’ dormitories, together with shared kitchen and leisure spaces, generating a sense of communal living.

The complex’s levels are staggered to maximise airflow to improve indoor air quality, a real benefit in the frequently high humidity of the region.

At the centre of the renovated school, Project Mingde designed a courtyard which provides a large, flexible area where villagers can meet and hold events.

“The design encourages social interaction, allowing villagers to forge and strengthen community bonds, an essential aspect of life in a Hakka village,” said Elisabeth Lee.

Materials were locally sourced and feature vernacular red brick and pine timber chosen to blend with surrounding buildings.

The new complex is the second phase of Project Mingde’s work in Duling. Work is also completed on the existing primary school building, with a new waterproof roof and a sustainable toilet to address the school’s previously poor sanitary facilities.

The HKU Department of Civil Engineering Project Mingde was established in 2003 to provide real life experience for students while helping to relieve the problems of the impoverished population of the remote Guangxi Province.

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