Make an extension from the terrace?

Hello everyone,

we are currently in the renovation phase of our own four walls, and more and more the wish/idea came up to extend the existing terrace into living space.

On the one hand, because the garden is quite large and can be used better this way, and on the other hand, because the living area could be designed much better this way.
Additionally, the currently existing pergola needs to be demolished because it is partially no longer load-bearing.

The single-story new building is to be made of aerated concrete blocks and offer a wide window front.

Is it possible to raise the existing terrace foundation by about 40cm with the appropriate screed concrete?
A joint tape between the screed of the old and new construction is necessary; will the walls be sealed accordingly (if at all)?

This is initially a rough plan to be able to determine what costs and effort to expect and whether it might be necessary to fully hire a construction company.

Thanks in advance.

First of all, a building permit for the extension of the living space is required. So: first step to the building authority, if positive, then to the architect who submits the building application. Then we will see further.

Good luck with the office. Tip: always be nice and friendly, then they will also be friendly in their response.

Best regards, Yvonne

The step at the building authority takes place, there is no development plan available and we still have about 5 meters in the surroundings that we are allowed to build on. Desired or wished for are about 3.5 meters

A normal terrace does not have a foundation but simply a frost-proof, compacted substructure made of gravel. The extension should be planned by an architect or master builder; simply botching it is nonsense.