The "Timber on top" project will produce a Best Practice Guide on how to work with vertical extensions (of buildings) in a socially, economically and ecologically sustainable way.

"Timber on Top - Stage 1", funded by Vinnova under contract 2018-02753, was led by Arbio – Sveriges träbyggnadskansli and was carried out during the period 2018-12-01 - 2019-08-31. The aim of stage 1 was to create a framework for stage 2 by mapping opportunities and obstacles for vertical extensions, linked to the three sustainability perspectives; social, economic and ecological sustainability. In the project, Arbio, LIU, LTU, RISE, Trästad Sweden, five municipalities and about 30 companies participated. In stage 2, the work will focus on developing, testing and analyzing process support, business models and technical solutions. The results will be disseminated through workshops and seminars and will be documented in a Best Practice Guide. Stage 2 of "Timber on Top" was granted by Vinnova in July 2019 and will run from autumn 2019 to autumn 2021.

This report presents parts of the work done in stage 1. The aim was to identify development needs to be addressed in stage 2 concerning social sustainability and urban development. The subject is broad, and a delimitation needs to be done in order for a best practice to be identified. In this pre-study, project participants' views and wishes were gathered by interviews, to be taken as a starting point for a relevant delimitation of the scope. Some examples of findings in this study are:

•

There is a need for better understanding of municipal planning processes. For example, how cultural values can be taken care of in extension projects and whether and how planning processes can be more effective.

• It would be interesting to explore extension projects as a means of social innovation. Can vertical extensions be used to increase the social sustainability of residential areas with social challenges?

• The project participants wish to be informed of existing vertical extensions that represent good and bad examples. They also want to meet physically in the project and to get in touch with builders and architects who have experiencein vertical extensions.

Vinnova and the participating companies are hereby warmly thanked for funding and for the opportunity to complete the project's first phase. A special thank you also to project participants in Umeå, Varberg, Växjö, Sunne and Malmö for your time and commitment in this study.