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11 December, 2023

Built by Nature awards €211,000 to demonstrate potential of timber-based vertical building extensions in European cities

AMSTERDAM December 11. The Built by Nature Fund has awarded € 211,000 to a UK, Dutch and Spanish consortium for development of an open-source knowledge and technical information platform to raise awareness and understanding of how vertical extension of our buildings and cities using mass timber can unlock much-needed floor area, create new carbon stores, and keep construction emissions to a minimum.  

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.  

 “This project demonstrates the compelling potential of extending our existing buildings upwards rather than demolishing them and replacing them with new ones, saving huge quantities of embodied carbon, while creating new and attractive urban spaces that simultaneously store carbon.”

according to Built by Nature CEO Paul King.

“We believe that many asset owners, developers, investors and city governments are simply not aware of the potential of these ultra-low-carbon rooftop extensions, and this Built by Nature-funded project hopes to bolster understanding of this exciting opportunity.”  


Kelly Harrison, Director, Whitby Wood (project lead), said,

“The construction industry needs to drastically decrease its impact on our climate, and there are ways it can do that with the technologies and resources we have today. 

“Optoppen is a multi-benefit solution to our need to provide new space in our cities: it is the process of adding to our existing buildings with materials like mass timber that store carbon and that are replenished, using the value created by the additional floor area to upgrade the energy efficiency of the original building below. 

“We’re delighted to have been awarded funding for this year-long project unlocking Optoppen at city scale by creating an interactive tool for climate-conscious property owners and city planners, a database of existing case studies, and an analysis of current policies across Europe. We look forward to working with Built by Nature’s network and the wider industry to make Optoppen more commonplace.” 


The Built by Nature Fund and the project team see the Optoppen project as benefitting important audiences: from policy development at a local government level; allowing a better understanding of property valuation and carbon storage potential for an asset owner, and for a developer to acquire the knowledge to inform redevelopment briefs and to champion Optoppen over demolition and rebuild. 


For further information, contact  

Karianne Kraaijestein, Built by Nature  

Or Rosie Cade, Rising Tide (Optoppen project team),  


About Whitby Wood
Whitby Wood is an independent, international and forward-thinking engineering consultancy. It works on the structural, civil and geotechnical engineering design of buildings and urban infrastructure, providing professional services for clients working in all sectors. Whitby Wood supports sustainable construction, and works hard to develop practical cost-effective design solutions, for projects large and small. 

Working closely with like-minded colleagues in diverse engineering fields, Whitby Wood focuses on the whole technical challenge a project presents. The work is based on in-depth knowledge of best practice — locally, nationally and internationally — and an openness to innovation.