Xifré’s Rooftop: “Floating” Wild Garden

Basic information

Project Title

Full project title

Self-sufficiency, social interaction & biodiversity designed into a heritage rooftop renovation

Project Description

This project has been a fantastic opportunity to reintroduce nature to the heart of Barcelona. The Xifré Rooftop is a dual purpose renovation project, in terms of both architecture and ecology. Covering an early 19th-century block of ten buildings, this contemporary roof garden creates a “floating” wild space that enhances urban biodiversity and opportunities for social interaction between neighbours. Furthermore, the rooftop elements of the historic building have been carefully restored.

Project Region

Barcelona, Spain

EU Programme or fund

Description of the project

Summary

In 2017, when the Barcelona City Council launched the green roofs open competition Sergio Carratalá, the founder of MataAlta Studio, saw an opportunity to use his structural engineering expertise to develop innovations in this relatively new design discipline. He understood how to reintroduce nature in the middle of this densely built Mediterranean city, using a strategic combination of engineering know-how and sustainable technologies.

In winning the city council competition MataAlta Studio was able to realise a rooftop garden that met exceptional standards in green roof design, while paying respect to the history of the site by giving equal weight to architectural heritage and local ecology. Els Terrats d’en Xifré is a renovation project across the top of an early 19th-century block of ten buildings in the old town of Barcelona. The building houses restaurants on the ground floor, and many residential apartments and tech company offices.

One of the key aspects of this project is the reversibility of the rooftop design. By using a ballasted multilayer technical solution, Carratalá avoided attaching the garden directly to the building. In fact, the structure “floats” on top of the building, lying on top of the existing terrace. This highly respectful approach allows the whole project to be fully reversible.

MataAlta Studio’s design prioritises the spirit of circularity in the way it recycles resources such as water, energy and carbon. The vision for the rooftop is a highly accessible community space that promotes social interaction, discovery through play and people’s physical and mental wellbeing.

MataAlta Studio runs a programme of workshops and family activities over the seasons, providing educational opportunities for residents to learn from nature. The Xifré rooftop is different from the usually understood concept of green roof design because of its focus on boosting urban biodiversity, strengthening social networks and respecting heritage.

Key objectives for sustainability

5 main design objectives:

Heritage. The project is located on top of a 1830’s landmark. Els Porxos d'en Xifré is a historical site protected under the Barcelona city heritage program. This status meant the roof required significant renovation to restore its architectural heritage before developing the green roof’s urban ecology.
Biodiversity. To encourage biodiversity, the garden features ponds, insect hotels and nesting structures. The planting uses more than 50 species and nearly 10,000 plants. Native perennials were chosen for their aromatic, pollinator friendly, drought resistant, pollution-filtering and disease resistant qualities. Providing year-round blooming these plants, along with the bird feeding and nesting places, restore local ecosystems.
Social. The rooftop offers a green living space for the residents of the ten-building block to enjoy. The garden plan avoids squared angles and straight lines, in contrast to urban grid patterns, to help visitors relax in a visually softer environment. The careful placing of curvilinear benches and plazas is designed to enhance social interaction between neighbours.
Low Impact. Materials have been strategically chosen to lower the carbon footprint and environmental impact of this project. From recycled brick-waste gravel to reclaimed timber from the original building; from traditional lime mortar to 0% use of Portland cement; and from FSC timber to local providers of native plant species. Even the structural design considers the remaining load capacity of the building to accommodate the earth dunes without any further use of materials for reinforcement.
Self-sufficiency. This project uses energy, water and carbon resources in a circular way. The design ensures that no additional water, electricity or fertilizer are needed. The solar panels provide energy, the rainwater harvesting system provides irrigation, while the use of green manure and composting techniques avoids the need for any chemicals in the soil.

Key objectives for aesthetics and quality

The Xifre rooftop has been designed as a multi-sensorial experience for users:

Sound - the rooftop is a retreat from the busy streets of the city below. Rising above the city, the planted vegetation absorbs the noise pollution. In this quieter space visitors can focus on the sounds of birds, insects, and the wind through the plants, which together create a relaxing symphony.
Smell - the planting on the rooftop has been carefully chosen for the fragrance of the herbs and flowers. This garden provides an all year round flowering design and a wide range of aromatic plants. The perfume from plants can have both a re-energizing and relaxing effect on people. As such the aim of the rooftop garden experience is to have visitors leave feeling refreshed and reinvigorated.
Taste - The rooftop garden introduces residents to urban agriculture at a domestic scale. A wide variety of edible and medicinal perennials have been included in the planting design to ensure residents can harvest their own thyme, lavender, rosemary, cherries and pomegranates. A number of raised beds allow for small vegetable patches where neighbours can grow food alongside each other, just meters away from their kitchens.
Touch - the rooftop garden is a tactile environment. Visitors can extend their hands to feel the smoothness of the curvilinear seating and brush past plants with many different textures. People are encouraged to walk on planted paving, to enjoy the sensation on their feet and legs, as though they were strolling in a wild flower field. With the raised vegetable beds residents can get their hands into the soil to nurture their flourishing vegetables.
Sight - as a retreat from the harsh environment of the city, characterized by rectilinear forms and hard surfaces, the rooftop offers a softer visual impression. The wild planting design, the meandering pathways, and curvilinear plazas provide an experience of nature without leaving the building.

Key objectives for inclusion

Five connections in terms of inclusion:

Community - the rooftop is designed with the building’s residents in mind. It is a space to relax, do gentle exercise, meet friends and neighbours, tend vegetables, and enjoy nature. The smart tag system allows residents to enter and exit the garden by tapping their key fobs on the door pad, ensuring a safe and secure environment.
Discovery - as a multi-sensory space there is a lot to explore in the Xifre garden. The use of natural materials means the rooftop is a safe and healthy environment for children to play in. The space encourages the discovery of new sights, sounds, smells, textures and tastes. MataAlta Studio organises workshops and family activities over the seasons, to help residents and visitors learn from nature.
Conversation - designed as a social space where people can connect with each other, this rooftop is a neighbourhood park in the sky. The seating in the plazas encourages casual meetings between residents from the 10 buildings in the block, while also providing space for organised group meetings and picnics.
Accessibility - the rooftop is for all residents, and as such the accessibility of the garden for those with mobility issues has been considered. Specially adapted elevators, that accommodate wheelchair users, transport people efficiently to the rooftop. For those who want to use the garden as a recreational or work space there is a free wifi network on the roof and power points strategically placed in the social areas to plug in electrical devices.
Health (physical and mental) - the natural environment provided by the garden design is a place of restoration for plants, animals and humans alike. The ring path allows for walking, where neighbors can engage in conversations or enjoy a peaceful time in meditation with the flowers. The positive effects of natural green spaces of gardens on people’s physical and mental health have been well studied, as have the positive effects of gardening.

Results in relation to category

To make our cities more energy and material efficient, they need to be densely inhabited. However, this objective of intensifying the use of urban space is hard to balance with the human need for a healthy habitat; clean air, greenery, and biodiversity in our ecosystem. The Xifre rooftop project proposes one solution to this problem.

By introducing biodiverse natural systems on top of our buildings, a busy city such as Barcelona can serve both human’s and nature’s needs and have them be interdependent. As famous urban planner Idelfons Cerdà said “lets ruralize cities” by effectively introducing wild gardens in every gap of our cities. Considering that 67% of buildings in Barcelona (1.700 Ha) have flat accessible roofs, this solution has a huge potential to improve the quality of life of people with a healthier, more resilient, self-sufficient city.

This building renovation has surpassed all expectations in terms of regeneration of the urban ecosystem. The number of insects, birds and reptiles that now thrive in this oasis proves the success of the intervention. There are several small ponds where fish, amphibians and insects thrive in ecological balance. These water features boost the ecological value of the project.

Perennial native plants such as pistacia lentiscus or tamarix provide birds with feeding fruits and nesting places. The population of butterflies and insects has boomed all over the place, due to the specific planting design that provides year-round flowering meadows. The garden design includes the creation of insect and reptile friendly habitats through the installation of piles of wood and rocks that mimic their natural ecosystem environment.

After only 2 spring seasons, this safe haven for urban wildlife now hosts several bird species, some of which have successfully nested in the green roof, such as the european starling (Sturnus vulgaris), the Eurasian blackcap (Sylvia atricapilla), and the black redstart (Phoenicurus ochruros).

How Citizens benefit

The owners, the residents and the city have benefitted from the construction of the project in various ways.

City Benefits:

Biodiversity and habitat improvement (healthier and more resilient urban ecosystem)
Urban landscape aesthetic improvement (taller buildings and higher viewpoints can enjoy the garden)
Waste diversion (by using recycled and retrofitted long lasting materials)
Stormwater management (the project can retain 70-90% of the precipitation that falls on it, flattening the discharge curve during floods)
Moderation of Urban Heat Island Effect
Improved air quality (plants filter air pollution and capture CO2)
Local job creation (all companies and contractors involved in the project are local)

Residents benefits:

Community hub (the high quality communal space allows for social interaction and neighbours bonding)
Energy efficiency (insulation effect of the garden reduces up to 23% in energy consumption for heating and 75% for cooling)
Noise reduction (Green roof and plants can reduce between 10-50 decibels)
Improved health and well-being
Educational opportunities (from MataAlta’s workshops, activities or mere nature observation)

Owners benefits:

20% increased proprietary value (Several tech companies have rented office space thanks to the project appealing to them)
Increased roofing membrane durability (the project lowers the exposure of waterproofing to large temperature fluctuations, and ultraviolet radiation)
Renovation and rehabilitation of the building (during the sensitive renovation of the historical building in the process of installing the rooftop garden)
Award winning design project (improves the visibility of the property in the market)

Innovative character

Green roof as climate shelter - Inspired by C40 Knowledge project “Cooling Schools” this project shows how apartment buildings with strategically vegetated rooftops can act as cool islands in the city. These hubs bring heat-health-awareness to homes and businesses, while adding a safe and low impact solution to outdoor space, even during hot summer months.
Smart Structural Design. This project pays respect to the building’s original materials, construction techniques and 1830 architectural heritage. No structural retrofitting was implemented in the project. Comprehensive structural analysis was carried out to map the bearing capacity of all structural elements involved, before starting the garden layout. Inspecting, cataloguing and repairing the 250 year old timber structure revealed the structural capacities for all areas of the roof. This was the key to the design, enabling the safe installation of earth dunes hosting a biodiverse range of plants.
Rewilding the City. This project proposes that rewilding the cities with nature, that existed before the buildings, can reestablish a healthy environment for all living creatures. The project features ponds, insect hotels and nesting structures. The planting design includes more than 50 species and nearly 10,000 plants chosen for their biophilic value, providing year-round blooming, bird feeding and nesting places, enabling local ecosystems to be restored and strengthened.
“Floating” Wild Garden Concept. Following the respectful approach to architectural heritage, the project created a fully reversible design where no new feature is attached to the original elements. From the root-resistant waterproof membrane to the multilayered technical solution, everything floats unattached to the building, ballasted by the weight of the earth dunes, built-in benches and gravel paths. This design approach ensures no permanent impact is inflicted on the building and a clean removal of the garden is always possible.