The Bartlett School of Architecture


Building Greener Cities with Poikilohydric Living Walls

St Annes wall with moss for the ‘Le Fabrique du Vivant’ exhibition at the Centre Pompidou - detail. Photo Credit: Sarah Lever

The city is both culprit and victim: guilty of continuing to employ unsustainable material and construction solutions that lead to increased temperatures and a higher intensity of water vapour in the air – and victim, faced with a dual challenge of being both water stressed and vulnerable to flooding.
For Marcos Cruz, Professor of Innovative Environments at The Bartlett School of Architecture, breaking the dilemma requires a shift to bio-integrated architecture, where hydrophilic conditions are embedded in building and material design.

“All the externally exposed surfaces of buildings and urban infrastructures, from blank walls and facades to roofs, retaining barriers and fences offer vast quantities of area to absorb and store water," said Marcos. "Hydrophilic design allows us to take advantage of plants that will help us improve the storm-water management of facades and increase absorption of CO2, nitrogen and pollutants while emitting significant levels of oxygen.” 
Marcos isn’t talking about the typical concept of the green wall, which, he says, has something of the golf course about it: an expectation that it should be lush and green regardless of the season, resulting in monocultures requiring a lot of maintenance and artificial irrigation. 
Instead, it is the humble poikilohydric plants – algae, mosses and lichens – that interest him, because they are able to deal with lengthy dry spells simply by “turning down their cellular metabolism – becoming dormant until new water intake enables them to photosynthesis again”. But for these plants to bio-colonise the city, they need more diverse and suitable bioreceptive substrata – what Marcos calls architectural ‘barks’ in the article Bioreceptive Design (Cruz, Beckett, ARQ 2013), to encourage their growth.

Prototyping in partnership

Developing the kind of building cladding able to support this biological strategy was initially developed in collaboration with colleague Richard Beckett and then the subject of an EPSRC-funded grant ‘Computational Seeding of Bioreceptive Materials’, which was concluded in April 2017. The team was led by Marcos and included biologist Dr Sandra Manso – who originally developed a type of porous MPC concrete at UPC in Barcelona – as well as Richard Beckett and Dr Chris Leung from The Bartlett and Bill Watts from Max Fordhams LCC, in partnership with Laing O’Rourke. It has been taken forward since 2017 through a new industrial partnership with Pennine Stone Limited with a series of three pilot projects. 

EPSRC Bioreceptive Panels at Bartlett Hampstead Road

“For this to work, we need novel morphological and material construction systems to support the plants," Marcos explained. "This includes upgrading current bioreceptive systems to allow far more water absorption in the materials than what has been possible to date, in order to prolong water availability to feed plants. We also need to be able to be selective about which areas of the building facade store water and which remain dry, so that we can promote continuous growth where we want it.”
In addition, the geometry of the surfaces needs to be able to intensify water catchment on the facades; there also needs to be a textural variance of recesses and protrusions to help plants stay attached when desiccated or threatened by prevailing winds. Achieving this kind of surface complexity has meant working across micro (material), meso (surface) and macro (tectonic) scales (Cruz, Beckett, ARQ 2013). The partnership with Pennine Stone has been critical to Marcos being able to develop it with a view to producing a commercial product.

Bio-ID and planting urban pilot projects 

“The aim is to develop far more biologically integrated systems than what we have available today; there needs to be a portfolio of options to cater for different climates and microclimates," said Marcos and his colleague Dr Brenda Parker from UCL Department of Biochemical Engineering, who created the award winning Bio-ID (Bio-Integrated Design) as an interdisciplinary platform to develop in depth research and enterprise to produce radically new solutions for the built environment. With their team they are testing new biochemical processes on a variety of materials scaffolds to be apply on three walls in different locations in the UK.
The first poikilohydric wall of 32 GRC Limestone concrete panels was installed in September 2020 as a trial at the St Anne’s Catholic Primary School in South London. It was developed and designed in collaboration with colleague Javier Ruiz as well as Richard Beckett and supported by the London Borough of Lambeth and Transport for London. The manufacturing was done by Pennine Stone, while research of moss growth was developed with help from biologists Anete Salmane and Rushi Mehta, and the construction of the first prototype exhibited at the Centre Pompidou in February 2019 included students from UCL Bio-ID. The second installation is planned to be built out of 20 GRC Limestone concrete panels at East Putney Station in London. TfL are interested in the results because bio-receptive walls have the potential to do away with costly maintenance and also are capable of absorbing pollutants from the air. Both projects will provide crucial observational studies for the next three years.

The study of the microbiome of mosses to be grown on new bio-mineral substrates is currently being carried out in Bio-ID by PhD student Alexandra Lacatusu who gained an EPSRC-DTP scholarship for this purpose. Previous structural tests were also done with the support of Dr Hector Altamirano at The Bartlett and the Department of Civil, Environmental and Geomatic Engineering in collaboration with the UK Centre for Moisture in Buildings. In addition to the environmental and aesthetic benefits, both poikilohydric walls will offer the opportunity to explore how the morphology of the bioreceptive design could reduce noise from the busy main road running alongside the school’s playground (St Anne’s) and the trains that pass the station (East Putney). 

The third iteration, due in late 2021, will be an installation of a smaller poikilohydric wall made of 10 GRC limestone cork-crete panels integrated in building extension at Merchiston Park in Edinburgh. The underpinning research is underway with the University of Coimbra (Prof Fernando Branco) and the Technical Institute of Tomar (Dr Lurdes Belgas) as well industrial partners Amorim (ACC) in Portugal, where additional mixes of natural and expanded cork are being investigated as an alternative aggregate. The aim is to promote the growth of Lichens along with mosses and test the long term carbon offset by the photo-synthetic activity of the plants. Smaller samples are being exposed at the Meanwhile Wildlife Gardens and Camley Street nature Park in London. 

In the long term, Marcos and Brenda have other ambitions. “The synthetic bio-silicification and bio-sedimentation of materials offers us the opportunity to move away from the idea of buildings being only scaffolds for outer growth. We are envisioning a radical change in which 20%, 30% or more of our future construction could become grown rather than manufactured with large surfaces being biocolonised, ultimately making our future cities photosynthetic.” 

Interested in finding out more about the project? Contact Professor Marcos Cruz at m.cruz@ucl.ac.uk



The current research is carried out in Bio-ID, led by Dr Marcos Cruz, Professor of Innovative Environments at The Bartlett School of Architecture and Dr Brenda Parker, Associate Professor of Sustainable Bioprocess Design in the UCL Department of Biochemical Engineering, with PhD candidate Alexandra Lacatusu.
The EPSRC-funded research team for Computational Seeding of Bioreceptive Materials included Professor Marcos Cruz (PI), Richard Beckett, Dr Sandra Manso, Dr Chris Leung and Bill Watts.

Key partners

Lead image: St. Anne's Primary School wall with moss for the ‘Le Fabrique du Vivant’ exhibition at the Centre Pompidou. Photo Credit: Sarah Lever

Other images: EPSRC Bioreceptive Panels, at Bartlett Hampstead Road

Carousel 1:
1. East Putney wall: drawing for site
2. East Putney wall: rendering
3. East Putney wall: moulds for casting
4. East Putney wall: casting at Pennine Stone

Carousel 2:
1. St Annes Primary School wall panels for ‘Le Fabrique du Vivant’ exhibition at the Centre Pompidou.
2. St Annes Primary School wall: Axo with fixings
3. St Annes Primary School wall during manufacturing at Pennine Stone
4. St Annes Primary School wall: casting at Pennine Stone

Carousel 3:
1. Edinburgh wall: drawings for site
2. Corkcrete samples at Meanwhile Life Gardens
3. Corkcrete samples at University Coimbra
4. Poikilohydric growth on porous concrete

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