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Miguel Angel 23, Madrid

New envelope drives sustainable office retrofit in Madrid

Real estate owners are looking for strategies to upgrade existing commercial stock amid a major reshape of the way we work and use our offices. In Madrid, property company Colonial was looking for a sustainable way to refurbish this commercial office building, with more than 8,000 m₂ of prime office space in the city’s central business district. 

Initially developed in the 1970s, Colonial wanted the property at Miguel Ángel 23, next to Paseo de la Castellana, to become a flagship office building with a low carbon footprint and near-zero energy consumption. Working with Fenwick Iribarren Architects, Arup was tasked with designing a sustainable and highly efficient façade, delivering a see-through building envelope showcasing the unique office space and its occupants. 

Our team of building envelope designers and sustainability consultants designed an elegant, sustainable solution for the façade: a timber curtain wall with an external timber louvre system that lends the building a distinctive character while extending its durable life.  

Acting as a carbon sink, timber is increasingly in demand for property development, and plays a leading role in a number of infrastructure design concepts; with a growing number of studies exploring water and fire safety considerations.  

To establish durability and explore the opportunity cost for this timber building envelope, our team carried out an extensive assessment Life Cycle Analysis and the Life Cost Analysis for a low-carbon timber solution and a conventional, carbon-intensive material. The study showed that, despite the maintenance requirements, the use of timber reduced the embodied carbon by 66% and provided a cost-effective investment solution for this retrofit.

Project Summary

8,204 m2 gross floor area

41tCO₂ saved


A façade with a low carbon footprint for the building

Updating tired commercial property buildings will play a role in the decarbonisation of the built environment. Alongside other carbon-saving interventions, a new building envelope can extend the lifespan of an existing asset by another 30 years.  

Reducing carbon impact is the main driver behind this retrofit, which repurposes this existing office building into a future-ready prime commercial space incorporating the use of low carbon materials in interior finishes as well as the façade.

Miguel Angel 23 façade Miguel Angel 23 façade

Selecting the right materials can result in large reductions to a building’s environmental impact: the use of local timber for this curtain wall has helped save 41 tonnes of CO₂ emissions.

The curtain wall and window frame are made of sustainable chestnut timber, with timber mullion and transoms with aluminium cladding, while the external façade timber louvre system is made of pine from PEFC and FSC-rated forests.

Energy-efficient building envelope

A façade’s thermal transmittance – or rate of heat loss - plays a major role in a building’s energy demand and requires a solid, sustainable design approach. To optimise the overall energy performance of this building retrofit with north and east-facing external façades, the team has designed an energy-efficient building envelope, with a timber louvre shading system on every floor and highly insulating triple-glazing. The glazing, which features a solar control treatment to deflect excess thermal gain from radiation; is paired with interior blinds that reflect the light outwards. These different elements allow users great control of light and heat gain, ensuring light can flood into the space in winter, while preventing excess solar heat gain during the hotter summer months.

User-focus drives prime office retrofit

Occupant well-being drives the refurbishment of this centrally located premium office building. The window-to-wall ratio, which measures a building’s overall window area, has been maximized to enhance user comfort, providing occupants with expansive views over Castellana and creating a light-filled office space.  

In this refurbishment, the external façades boast a window to wall ratio of 70%, offsetting heat gain with a ratio of 50% for the internal courtyard façades.