Is a preliminary building permit possible for an additional garage?

Assuming there is a preliminary building permit for a property and it defines a living area of max 160m2. Can a garage be built in addition to this? Is the total area allowed to exceed 160m2? Would the garage have had to be explicitly approved in the preliminary building permit?

The preliminary decision serves to clarify exactly such questions. If that was forgotten, you can either submit a new preliminary decision or take the development plan and look it up. If there is no development plan, you would have to look at the surrounding buildings to see if the property size allows for a garage, in order to reach a similar floor area ratio II as the neighbors. But these are also questions that your local architect can answer for you without much thought.