Do I need a building permit to renovate?

Not for everything. Painting, floors and a bathroom refit that leaves structure and services untouched count as routine maintenance and need no permit under the Spatial Planning Act. As soon as you touch load-bearing walls, the layout or the facade, you need a permit from your municipality's chief architect. Ask the building department before you open a wall, and for work on the facade or common parts obtain the owners' meeting resolution as well. On tradespeople: get at least three quotes, inspect finished work in person, agree a fixed price with staged payments, and avoid large advance payments. Pay the final instalment only after handover, and take a receipt for every payment.