Under great demand in 1970 over 12 000 apartment buildings were built in Finland. These prefabricated buildings were mostly planned and built with terms and interests provided by the result-oriented building construction industry. This had an impact on the quality of the built environment. After five decades these mass-produced apartment buildings have maintenance backlog. Complementary construction is one way to fund upcoming extensive renovations.

This thesis is about building new additional storeys with modular elements above old apartment buildings. Complementary construction and renovation of the old housing stock is a sustainable way to make urban structure denser and diversify the old housing stock.

The concept plan in this thesis proposes modular elements to be used for new additional storeys in old apartment buildings. Two example cases show how standard sized modular elements as additional stories can provide variation for 1970 housing stock. The load bearing parts of these modular elements are cross laminated timber. The Stora Enso’s Building System was applied in the concept plan as a structural and technical guideline. The Buildings and the housing companies are featured in the concept plan as example cases and they are unlinked into this thesis.

From this thesis was observed that it is possible to build additional stories in old apartment buildings with four divergent modular elements. Construction of additional stories can happen much faster with modular elements than with conventional building methods. This is crucial when construction takes place in an apartment building which is used during the construction. From the two example cases was seen that all old apartment buildings are not well suited for additional stories owing to the today’s building regulations and the characteristics of an old building.