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Trikåfabriken is a brick building from 1929 that has been given a five-storey upward extension in wood. Image: Tengbom

Building at a high level

If you’re building new, build higher and build with wood, says Timber on Top, a collaborative project that promotes sustainable urban development and a climate-neutral construction industry.

The Timber on Top project brings together the whole construction industry – from architects, property owners and contractors to municipalities, consultants and suppliers – to create a knowledge platform on how best to build wooden extensions on top of existing buildings. The collective expertise regarding the approaches used has highlighted several advantages of this construction method.

Tomas Alsmarker is the project manager for Timber on Top.
“Wood is a circular material that is also lightweight, making it possible to add several storeys to an existing building. It’s easier to build industrially in wood than with other methods on sites that are short on space, while details and features can be designed for easy assembly and disassembly. All construction needs to be based on circular materials, circular design and what has already been built. How can that be done? By building ‘on top’ instead of ‘on the ground’.

Upward extensions using bio-based materials such as wood can help reduce the waste of resources in the construction sector and expand the options for increasing housing where there is a lack of development land. Timber on Top is exploring these opportunities from a variety of angles in eight work packages, each with a different focus, such as the sustainable, economic and social elements of the construction method.

The project has a large number of partners, including several municipalities. Jessica Becker is an architect specialising in wood and project coordinator at Wood City Sweden, one of the organisations behind Timber on Top.

“Every municipality is grappling with these issues, the climate issue and the transition to circular and bio-based construction where materials can be reused and recycled. Several cities are actively working on the densification of inner-city areas and the refurbishment of the ‘Miljonprogram’ housing from the 1960s and 70s. We’re experiencing great interest from the municipalities. Extending upwards in wood on existing buildings is a good way to approach sustainable and climate-smart urban development,” she says.

Tomas Alsmarker believes that the knowledge bank could be of great help in future urban planning:
“Municipalities are pushing for a climate-neutral construction sector. Timber on Top can help to achieving the goal of a climate-neutral Sweden by 2045. The website, for example, offers a starting point for a municipality or a developer, when planning and costing an extension project, and working out how to make the whole business circular,” he explains.

BRF Glitne, the townhouses built on the roof of Utopia shopping mall in Umeå, and the modern offices at the top of Trikåfabriken in Hammarby Sjöstad in Stockholm are examples of eye-catching wooden extensions, and Timber on Top worked on both projects.

Jessica and Tomas continue:
“The eight work packages developed so far and available on are a foundation, a platform to build on. Municipalities, developers and other stakeholders don’t have to start from scratch, but can draw instead on the knowledge developed in the different work packages.”

Wood City Sweden provides the knowledge platform and acts as a hub for feeding back experience and knowledge from the projects to the various work packages.

“Each new extension project can be started from a slightly better state of knowledge. Timber on Top works on an open-source basis, which also makes the knowledge platform much more of a living resource,” says Jessica.

Text: Hanna Melin
Image: Tengbom

Published: 2021-10-14


"Every municipality is grappling with these issues"

Jessica Becker, architect


“All construction needs to be based on circular materials"

Tomas Alsmarker, project manager for Timber on Top

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