Nadgradnja Poljanska – Roška by Arheja

XLam City Top, also known as the Poljanska-Roška extension, is an excellent example of upgrading an existing building with a timber structure. It is a two-story older building that could have been demolished, generating at least 1,500 tons of construction waste. A new, five-storey building would then have required around 3,800 tons of concrete, resulting in at least 1,000 tons of CO₂ emissions.

With seismic retrofitting, 380 m³ of concrete were added to the building, corresponding to about 100 tons of CO₂ emissions. However, the timber extension, made of cross-laminated panels, stores 400 tons of CO₂ within the structure. The project therefore represents a responsible and sustainable solution, as the load-bearing structure has a negative carbon balance. Through carefully planned upgrading, the older, energy inefficient building has been transformed into a modern, energy efficient, and earthquake resistant structure, while preserving urban continuity and the historical character of the area.