A wall that looks purely cosmetic can actually be structural under the building's original 1960s–1980s plans. This isn't a rare edge case. Many buildings from that era used interior block walls as part of the structural design in ways that aren't visible or obvious without checking the original architectural plans. A contractor eyeballing the wall on-site can't reliably tell the difference — only a structural engineer reviewing the actual building plans can confirm it.
The risk isn't just cost. If a load-bearing wall is removed or altered without proper structural engineering and permit approval, it can affect the safety of the apartments above, create serious liability, and in some cases trigger a permit rejection that stops the entire renovation mid-project — after demolition has already started and the wall is already open.
The fix is inexpensive relative to the risk: before finalizing any renovation plan that touches an interior wall, request the building's original structural plans from the municipal archive and have an engineer confirm what's actually load-bearing before demolition begins, not after. This is a small, specific step that gets skipped surprisingly often, usually because it adds a week to the planning phase that owners are impatient to get past.
If your renovation plan includes opening up a wall between rooms — especially in a building from before the 1990s — this is the one question to ask before anyone picks up a sledgehammer.