The Institute for Advanced Architecture of Catalonia (IAAC) has secured funding from Built by Nature, forming a crucial part of a consortium spanning the United Kingdom, the Netherlands, and Spain. This significant development comes as the Built by Nature allocates €211,000 to demonstrate potential of timber-based vertical building extensions in European cities thanks to Optoppen.


Optoppen, or topping up, increases the useable space in a building through lightweight roof extensions, using timber in the process to create a carbon sink on top of cities, contributing to both urban decarbonisation targets and densification strategies. With Europe’s cities facing housing crises, Optoppen, as an alternative to demolishing a structure to build newer and bigger, saves existing embodied carbon while enlarging the building’s space with a low-carbon material that additionally stores biogenic carbon.
Led by engineering consultancy Whitby Wood, the project’s implementing partners – Mule Studio, New Urban Networks, Holland Houtland, Institute for Advanced Architecture of Catalonia (IAAC), Creative City Solutions, and Rising Tide – will, over the course of 2024, develop important resources and tools to help building owners, city planners and investors understand and test out the potential for Optoppen in their portfolios and places.

Central to the project is an interactive and dynamic website that allows asset owners and cities to quickly understand their vertical extension potential, providing a high-level structural assessment and reporting the possible amount of floor space area that could be created, and carbon stored in the mass timber. Optoppen projects will focus on common building types in European cities, with a focus on the UK, the Netherlands and Spain, with estimations available at both building and city levels.

Supporting outputs include an inventory of existing case studies; a live project from the Netherlands; an analysis of European policies; and communications and outreach activities including media updates, launch events and workshops in the UK, the Netherlands and Spain, inviting interested stakeholders from Built by Nature’s networks and beyond. Read the full statement.