The short answer first: it depends on the canton, the municipality and the type of work — there is no universal list. In the canton of Zurich, the Planungs- und Baugesetz (PBG, the cantonal planning and building act), together with the cantonal Bauverfahrensverordnung (building procedure ordinance), determines which projects require a permit. As a rule of thumb: pure maintenance work that changes nothing about a building's appearance or use usually needs no permit. As soon as the floor plan, the facade, the use or the load-bearing structure changes, a permit is required.
Usually possible without a building application
Interior renovations that change nothing about load-bearing walls, the structure or the building envelope can generally go ahead without a permit: new floor coverings, a new coat of paint, replacing sanitary fixtures in the same position, a new kitchen within the existing layout. Replacing windows with ones of the same size and in the same position is also often subject only to notification rather than a permit — the exact line is drawn by each municipality.
Usually with a building application
As soon as a load-bearing wall is moved or removed, the layout of a bathroom changes significantly (a new wet room in a new location with new riser zones), something is altered on the facade or the roof (new window openings, a balcony, a roof extension) or the use changes (e.g. from a flat to commercial premises), a building application to the responsible municipality is generally required. Properties in the core zone (Kernzone), listed buildings and properties subject to special building and zoning regulations are often subject to additional conditions.
In most municipalities in the canton of Zurich, processing an ordinary building application takes anything from a few weeks to several months, depending on the project, any appeals lodged by third parties and the workload of the building authority. This needs to be in the schedule from the outset: starting the works later does not shorten the processing time, and work may only begin once the permit is legally binding.
What we do in practice
During the site visit, we tell you whether we consider your project to require a permit and, if in doubt, recommend checking with the building department of the municipality where the property is located — the municipality makes the binding decision, not us. If a building application is needed, we supply the plans and information required for the relevant phase of the works, schedule the start of work only once the permit is legally binding and, for blocks of flats and property managers, point out possible appeal periods at an early stage.
This article is not a substitute for legal advice or for building advice from the municipality. What counts is always the decision of the responsible building authority where your property is located.